**3. The characteristics of muscle activity during walking in water**

## **3.1. Muscle activity in lower limb muscles**

enable longer EMG data collection periods due to increased comfort the suit provides in the water environment. However, the suit would disadvantage subjects who do not fit the standard size of the suit, and this waterproof method still requires further refinement to limit

**Figure 2.** Electrodes and its codes attachment for underwater EMG experiment. [Picture was taken by the authors]

The other issue for EMG recording in a water environment is whether the EMG data is affected by water immersion, even if the electrodes are waterproofed. However the EMG data seems to have little attenuation from water immersion if the waterproofing is completely imple‐ mented [10, 13-16]. There are numerous studies regarding the influence of water immersion for EMG data collection using waterproofed and non-waterproofed electrodes attached on human muscles [10, 13-16]. Rainoldi et al. [13] investigated the effect of EMG recording by using surface electrodes attached on Biceps Brachii in conditions of dry land, in water with waterproofed or not. The subjects conducted 50% of isometric maximal voluntary contraction (MVC) as determined by a load cell. The results showed that there was no attenuation on EMG recordings in averaged rectified value (ARV) and root mean square (RMS) value with water‐ proofed condition, whilst the non-waterproofed condition showed significant reduction of the EMG data. In addition to that, the same circumstances were seen in the signal spectrum analysis. The authors concluded that waterproofing was required for EMG recording in water environment to avoid large signal artifacts, to ensure constant recording conditions for the whole experimental session duration, and to avoid time consuming alternative correction technique to remove low frequency artifacts. Pinto et al. [14] investigated the effect on surface EMG recording of isometric MVC between on land and in water. The EMG was recorded from Biceps Brachii, Triceps Brachii, Rectus Femoris and Biceps Femoris. The results showed that the EMG data of each muscle was not affected by water immersion, however the force production of the hip extension decreased significantly in water. This study also reported a significant intra-class correlation coefficient from moderate to high (0.69-0.92) for the EMG recording and the authors concluded that the environment did not influence the EMG data in MVC. With respect to a reduction of EMG data without waterproofing in water environment, Carvalho et al. [15] reported that the reduction was around 37.1-55.8% in the water condition without waterproofing compared with the land or the water with waterproofing in both MVC and 50% of MVC trials. Recently, Silvers et al. [16] reported the validity and reliability of EMG

water intrusion at the openings [10, 12].

216 Electrodiagnosis in New Frontiers of Clinical Research

**2.2. The effect of human water immersion on EMG data**

One of the most basic forms of exercise in water is walking gait. Walking in water provides significant changes on your body. A number of investigations have been conducted on the physiological aspects of water walking [17, 18, 19], and more recently, biomechanics and kinesiology research has been published [11, 20-25]. Research into muscle activity has focused mainly on lower limb muscles due to the fact that walking exercise in water is generally conducted at the waist depth or deeper [8, 9, 18, 19]. Research of the lower limb muscles activity during walking in water has been reported by the authors at subject's self-selected slow, moderate and fast speed in comparison to those same selected speeds for land walking [11, 20]. Subjects included nine young men and they walked along the swimming pool deck for the land trial and in a 1.1m deep swimming pool. The EMG data was collected from Tibialis Anterior (TA), Soleus (SOL), Medial Gastrocnemius (GAS), Rectus Femoris (RF), VastusLa‐ teralis (VL), and Long Head of Biceps Femoris (BF) on subject's left side with 2000Hz sampling rate. The EMG data was normalized by MVC on land in each muscle. Data processing involved the raw EMG data being filtered using 4th-order low-pass and high-pass filters with cut-off frequencies of 500 Hz and 10 Hz, respectively. And then, the filtered EMG data was transferred to digital data, and the root mean square (RMS) of each phase calculated on a 100-ms window of data (i.e. 50 ms both before and after the data point of interest), and expressed as percentages of MVC (%MVC). This study evaluated the muscle activity in each cycle phase as to a stance phase from a heel contact to a toe-off, and a swing phase from the toe-off to the next heel contact. A paired Student's-t-test was applied for a statistical comparison between two conditions. Figure 3 and Figure 4 showed the result of the study.

As a result of the stance phase (Figure 3), significantly lower %MVC were observed during water-walking compared to land-walking in the SOL and GAS muscles at all speeds (P < 0.05). On the other hand, the TA and BF were significantly higher during water-walking than landwalking at normal and fast speeds (P < 0.05). In the swing phase, RF was significantly higher during water-walking than land-walking at all speeds, but the other muscles tended to be lower during water-walking than land-walking at all speeds especially in the TA (slow), SOL (moderate), VL (moderate and fast) and BF (slow and moderate) as significance (Figure 4).

Muscle activity during walking is not dramatically large if it is expressed in %MVC regardless of the condition. Basically, TA seems to activate during stance phase to stabilize the ankle joint against the water resistance added to whole body during water walking [21]. This may explain

why the TA activity was significantly higher during water-walking in moderate and fast speeds (Figure 3). There was no phase where the TA had to stabilize the ankle joint during swing phase, resulting in lower TA activity during water-walking than land-walking. How‐ ever, Nakazawa et al. [22] concluded that the inter-subject and intra-subject variability were higher in the TA response during water-walking. Therefore, more precise investigation of TA during water-walking is required. The muscle activity of SOL and GAS dramatically decreased during water-walking due to a reduction of weight bearing by buoyancy. Further investigation of these muscles by Miyoshi et al. [23] reported a different role of SOL and GAS muscles during water-walking. They concluded that the SOL was affected by walking speed and gravity stress, while the GAS was affected by only walking speed. In BF, more activation is needed to generate propulsive force against water resistance force by extending hip joint during stance phase. A larger hip joint extension moment during water-walking throughout the stance phase than that during land-walking was confirmed by Miyoshi et al. [24]. In the swing phase, the RF muscle activates more during water-walking than land-walking to overcome water resistance force for forwarding lower limb [21]. Interestingly, the %MVC of the other muscles decreased during water-walking compared to land-walking. It is presumed that this is due to a lack of or smaller impact force in water than that on land, reducing the need for VL and BF muscles to prepare for shock absorption at heel contact. As described above, lower limb muscle activity shows different modalities depending on walking style. phase from a heel contact to a toe‐off, and a swing phase from the toe‐off to the next heel contact. A paired Student's‐t‐test was applied for a statistical comparison between two conditions. Figure 3 and Figure 4 showed the result of the study. As a result of the stance phase (Figure 3), significantly lower %MVC were observed during water‐walking compared to land‐ walking in the SOL and GAS muscles at all speeds (P < 0.05). On the other hand, the TA and BF were significantly higher during water‐walking than land‐walking at normal and fast speeds (P < 0.05). In the swing phase, RF was significantly higher during water‐walking than land‐walking at all speeds, but the other muscles tended to be lower during water‐walking than land‐walking at all speeds especially in the TA (slow), SOL (moderate), VL (moderate and fast) and BF (slow and moderate) as significance (Figure 4). Muscle activity during walking is not dramatically large if it is expressed in %MVC regardless of the condition. Basically, TA seems to activate during stance phase to stabilize the ankle joint against the water resistance added to whole body during water walking [21]. This may explain why the TA activity was significantly higher during water‐walking in moderate and fast speeds (Figure 3). There was no phase where the TA had to stabilize the ankle joint during swing phase, resulting in lower TA activity during water‐ walking than land‐walking. However, Nakazawa et al. [22] concluded that the inter‐subject and intra‐subject variability were higher in the TA response during water‐walking. Therefore, more precise investigation of TA during water‐walking is required. The muscle activity of SOL and GAS dramatically decreased during water‐walking due to a reduction of weight bearing by buoyancy. Further investigation of these muscles by Miyoshi et al. [23] reported a different role of SOL and GAS muscles during water‐walking. They concluded that the SOL was affected by walking speed and gravity stress, while the GAS was affected by only walking speed. In BF, more activation is needed to generate propulsive force against water resistance force by extending hip joint during stance phase. A larger hip joint extension moment during water‐walking throughout the stance phase than that during land‐walking was confirmed by Miyoshi et al. [24]. In the swing phase, the RF muscle activates more during water‐walking than land‐walking to overcome water resistance force for forwarding lower limb [21]. Interestingly, the %MVC of the other muscles decreased during water‐walking compared to land‐walking. It is presumed that this is due to a lack of or smaller impact force in water than that on land, reducing the need for VL and BF muscles to prepare for shock absorption at heel contact. As described

Figure 4. The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during swing phase. [Modified from

**Figure 4.** The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during swing

LW WW

%

TA SOL GAS RF VL BF

\* \*

\* \*

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\* \*

\*

There are a limited number of studies investigating hip and trunk muscle activity during water‐walking, and the EMG data around hip and trunk muscles during water and land based walking [25, 26]. In the author's investigation [25], the surface electrodes were attached to the subject's left side and the muscles studied included Adductor Longus (AL), Gluteus Maximus (GMa), Gluteus Medius (GMe), Rectus Abdominis (RA), Obliquus Externus Abdominis (OEA), and Erector Spinae (ES, the position of L2). The data reduction methods were also applied with the same method as mentioned in lower limb analyzes. The EMG data collected by 2000Hz sampling rate was normalized by MVC (%MVC) on land in each muscle with 4th‐order 500Hz low‐pass and 10Hz high‐ pass filters, and the root mean square (RMS) on a 100‐ms window of data applied. Figure 5 and 6 showed the results of the

There are a limited number of studies investigating hip and trunk muscle activity during water-walking, and the EMG data around hip and trunk muscles during water and land based walking [25, 26]. In the author's investigation [25], the surface electrodes were attached to the subject's left side and the muscles studied included Adductor Longus (AL), Gluteus Maximus (GMa), Gluteus Medius (GMe), Rectus Abdominis (RA), Obliquus Externus Abdominis (OEA), and Erector Spinae (ES, the position of L2). The data reduction methods were also applied with the same method as mentioned in lower limb analyzes. The EMG data collected by 2000Hz sampling rate was normalized by MVC (%MVC) on land in each muscle with 4th-order 500Hz low-pass and 10Hz high-pass filters, and the root mean square (RMS) on a 100-ms window of

In the stance phase (Figure 5), the OEA was significantly lower %MVC during water‐walking than that during land‐walking in all speeds (P < 0.05). The RA showed significantly lower %MVC during water‐walking than land‐walking only in slow speed. A significantly higher %MVC was seen during water‐walking than land‐walking in the GMe and ES at fast speed. In the swing phase, the AL and ES showed significantly higher muscle activity during water‐walking than that during land‐walking at all speeds, however, all other muscles activity were lower during water‐walking than land‐walking in the OEA at all speeds, the GMa and

In the stance phase (Figure 5), the OEA was significantly lower %MVC during water-walking than that during land-walking in all speeds (P < 0.05). The RA showed significantly lower %MVC during water-walking than land-walking only in slow speed. A significantly higher %MVC was seen during water-walking than land-walking in the GMe and ES at fast speed. In the swing phase, the AL and ES showed significantly higher muscle activity during waterwalking than that during land-walking at all speeds, however, all other muscles activity were lower during water-walking than land-walking in the OEA at all speeds, the GMa and GMe at moderate, and the GMa and RA at fast with significant level (P < 0.05), respectively.

reference 11]

Student‐t's‐t‐test.

A: slow, B: moderate, C: fast.

LW: land‐walking, WW: water‐walking.

phase. [Modified from reference 11]

A: slow, B: moderate, C: fast.

(C)

LW: land-walking, WW: water-walking.

%

\*

%

TA SOL GAS RF VL BF

(A) (B)

TA SOL GAS RF VL BF

\*: significant difference between water-walking and land-walking (P < 0.05).

\*

\*: significant difference between water‐walking and land‐walking (P < 0.05).

**3.2. Muscle activity in hip and trunk muscles**

GMe at moderate, and the GMa and RA at fast with significant level (P < 0.05), respectively.

data applied. Figure 5 and 6 showed the results of the Student-t's-t-test.

**3.2. Muscle activity in hip and trunk muscles**

cut‐off frequencies of 500 Hz and 10 Hz, respectively. And then, the filtered EMG data was transferred to digital data, and the root mean square (RMS) of each phase calculated on a 100‐ms window of data (i.e. 50 ms both before and after the data point of interest), and expressed as percentages of MVC (%MVC). This study evaluated the muscle activity in each cycle phase as to a stance

Figure 3. The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during stance phase. [Modified from reference 11] A: slow, B: moderate, C: fast. LW: land-walking, WW: water-walking. \*: significant difference between water-walking and land-walking (P < 0.05).

\*: significant difference between water‐walking and land‐walking (P < 0.05).

A: slow, B: moderate, C: fast.

above, lower limb muscle activity shows different modalities depending on walking style.

LW: land‐walking, WW: water‐walking. **Figure 3.** The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during stance phase. [Modified from reference 11]

Figure 4. The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during swing phase. [Modified from reference 11] A: slow, B: moderate, C: fast. LW: land-walking, WW: water-walking. \*: significant difference between water-walking and land-walking (P < 0.05).

LW: land‐walking, WW: water‐walking. **Figure 4.** The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during swing phase. [Modified from reference 11]

#### \*: significant difference between water‐walking and land‐walking (P < 0.05). **3.2. Muscle activity in hip and trunk muscles**

A: slow, B: moderate, C: fast.

why the TA activity was significantly higher during water-walking in moderate and fast speeds (Figure 3). There was no phase where the TA had to stabilize the ankle joint during swing phase, resulting in lower TA activity during water-walking than land-walking. How‐ ever, Nakazawa et al. [22] concluded that the inter-subject and intra-subject variability were higher in the TA response during water-walking. Therefore, more precise investigation of TA during water-walking is required. The muscle activity of SOL and GAS dramatically decreased during water-walking due to a reduction of weight bearing by buoyancy. Further investigation of these muscles by Miyoshi et al. [23] reported a different role of SOL and GAS muscles during water-walking. They concluded that the SOL was affected by walking speed and gravity stress, while the GAS was affected by only walking speed. In BF, more activation is needed to generate propulsive force against water resistance force by extending hip joint during stance phase. A larger hip joint extension moment during water-walking throughout the stance phase than that during land-walking was confirmed by Miyoshi et al. [24]. In the swing phase, the RF muscle activates more during water-walking than land-walking to overcome water resistance force for forwarding lower limb [21]. Interestingly, the %MVC of the other muscles decreased during water-walking compared to land-walking. It is presumed that this is due to a lack of or smaller impact force in water than that on land, reducing the need for VL and BF muscles to prepare for shock absorption at heel contact. As described above, lower limb muscle activity

As a result of the stance phase (Figure 3), significantly lower %MVC were observed during water‐walking compared to land‐ walking in the SOL and GAS muscles at all speeds (P < 0.05). On the other hand, the TA and BF were significantly higher during water‐walking than land‐walking at normal and fast speeds (P < 0.05). In the swing phase, RF was significantly higher during water‐walking than land‐walking at all speeds, but the other muscles tended to be lower during water‐walking than land‐walking at all speeds especially in the TA (slow), SOL (moderate), VL (moderate and fast) and BF (slow and moderate) as significance

Muscle activity during walking is not dramatically large if it is expressed in %MVC regardless of the condition. Basically, TA seems to activate during stance phase to stabilize the ankle joint against the water resistance added to whole body during water walking [21]. This may explain why the TA activity was significantly higher during water‐walking in moderate and fast speeds (Figure 3). There was no phase where the TA had to stabilize the ankle joint during swing phase, resulting in lower TA activity during water‐ walking than land‐walking. However, Nakazawa et al. [22] concluded that the inter‐subject and intra‐subject variability were higher in the TA response during water‐walking. Therefore, more precise investigation of TA during water‐walking is required. The muscle activity of SOL and GAS dramatically decreased during water‐walking due to a reduction of weight bearing by buoyancy. Further investigation of these muscles by Miyoshi et al. [23] reported a different role of SOL and GAS muscles during water‐walking. They concluded that the SOL was affected by walking speed and gravity stress, while the GAS was affected by only walking speed. In BF, more activation is needed to generate propulsive force against water resistance force by extending hip joint during stance phase. A larger hip joint extension moment during water‐walking throughout the stance phase than that during land‐walking was confirmed by Miyoshi et al. [24]. In the swing phase, the RF muscle activates more during water‐walking than land‐walking to overcome water resistance force for forwarding lower limb [21]. Interestingly, the %MVC of the other muscles decreased during water‐walking compared to land‐walking. It is presumed that this is due to a lack of or smaller impact force in water than that on land, reducing the need for VL and BF muscles to prepare for shock absorption at heel contact. As described

> LW WW

Figure 3. The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during stance phase. [Modified from

**Figure 3.** The mean ± standard deviation (SD) of %MVC value in each lower limb muscle at each speed during stance

\*

\*

%

TA SOL GAS RF VL BF

\*

\*

\*

applied for a statistical comparison between two conditions. Figure 3 and Figure 4 showed the result of the study.

cut‐off frequencies of 500 Hz and 10 Hz, respectively. And then, the filtered EMG data was transferred to digital data, and the root mean square (RMS) of each phase calculated on a 100‐ms window of data (i.e. 50 ms both before and after the data point of interest), and expressed as percentages of MVC (%MVC). This study evaluated the muscle activity in each cycle phase as to a stance phase from a heel contact to a toe‐off, and a swing phase from the toe‐off to the next heel contact. A paired Student's‐t‐test was

shows different modalities depending on walking style.

above, lower limb muscle activity shows different modalities depending on walking style.

(A) (B)

TA SOL GAS RF VL BF

TA SOL GAS RF VL BF

\*: significant difference between water-walking and land-walking (P < 0.05).

\*

\*

218 Electrodiagnosis in New Frontiers of Clinical Research

(Figure 4).

reference 11]

A: slow, B: moderate, C: fast.

LW: land‐walking, WW: water‐walking.

phase. [Modified from reference 11]

A: slow, B: moderate, C: fast.

LW: land-walking, WW: water-walking.

\*

%

C)

%

\*: significant difference between water‐walking and land‐walking (P < 0.05).

\* \*

**3.2. Muscle activity in hip and trunk muscles** There are a limited number of studies investigating hip and trunk muscle activity during water‐walking, and the EMG data around hip and trunk muscles during water and land based walking [25, 26]. In the author's investigation [25], the surface electrodes were attached to the subject's left side and the muscles studied included Adductor Longus (AL), Gluteus Maximus (GMa), Gluteus Medius (GMe), Rectus Abdominis (RA), Obliquus Externus Abdominis (OEA), and Erector Spinae (ES, the position of L2). The data reduction methods were also applied with the same method as mentioned in lower limb analyzes. The EMG data collected by 2000Hz sampling rate was normalized by MVC (%MVC) on land in each muscle with 4th‐order 500Hz low‐pass and 10Hz high‐ pass filters, and the root mean square (RMS) on a 100‐ms window of data applied. Figure 5 and 6 showed the results of the Student‐t's‐t‐test. In the stance phase (Figure 5), the OEA was significantly lower %MVC during water‐walking than that during land‐walking in all speeds (P < 0.05). The RA showed significantly lower %MVC during water‐walking than land‐walking only in slow speed. A There are a limited number of studies investigating hip and trunk muscle activity during water-walking, and the EMG data around hip and trunk muscles during water and land based walking [25, 26]. In the author's investigation [25], the surface electrodes were attached to the subject's left side and the muscles studied included Adductor Longus (AL), Gluteus Maximus (GMa), Gluteus Medius (GMe), Rectus Abdominis (RA), Obliquus Externus Abdominis (OEA), and Erector Spinae (ES, the position of L2). The data reduction methods were also applied with the same method as mentioned in lower limb analyzes. The EMG data collected by 2000Hz sampling rate was normalized by MVC (%MVC) on land in each muscle with 4th-order 500Hz low-pass and 10Hz high-pass filters, and the root mean square (RMS) on a 100-ms window of data applied. Figure 5 and 6 showed the results of the Student-t's-t-test.

the AL and ES showed significantly higher muscle activity during water‐walking than that during land‐walking at all speeds, however, all other muscles activity were lower during water‐walking than land‐walking in the OEA at all speeds, the GMa and GMe at moderate, and the GMa and RA at fast with significant level (P < 0.05), respectively. In the stance phase (Figure 5), the OEA was significantly lower %MVC during water-walking than that during land-walking in all speeds (P < 0.05). The RA showed significantly lower %MVC during water-walking than land-walking only in slow speed. A significantly higher %MVC was seen during water-walking than land-walking in the GMe and ES at fast speed. In the swing phase, the AL and ES showed significantly higher muscle activity during waterwalking than that during land-walking at all speeds, however, all other muscles activity were lower during water-walking than land-walking in the OEA at all speeds, the GMa and GMe at moderate, and the GMa and RA at fast with significant level (P < 0.05), respectively.

significantly higher %MVC was seen during water‐walking than land‐walking in the GMe and ES at fast speed. In the swing phase,

Figure 5. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during stance phase. [Modified from A: slow, B: moderate, C: fast.

A: slow, B: moderate, C: fast.

reference 25]

A: slow, B: moderate, C: fast.

reference 25] LW: land-walking, WW: water-walking.

\*: significant difference between water-walking and land-walking (P < 0.05).

LW: land‐walking, WW: water‐walking. **Figure 5.** The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during stance phase. [Modified from reference 25]

> propulsion of the body. As evidence for this, the trunk forward inclination angle is larger during water-walking than land-walking (Figure 7), which is a counteractive reaction to deal

> **Figure 6.** The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during

Trunk muscles show different muscle activity between water and land based walking, as well as lower limb. However, when humans walk on a treadmill apparatus, most muscle activity decreased during water compared with land in both lower limb and trunk area [29]. In this case, the walking speed was set as one‐half to one‐third of the land walking in reference to the oxygen consumption [17]. Furthermore, muscle activity during treadmill water‐walking without water flow further decreased muscle activity than with flow set to the same speed to the walking speed [29]. The differences between with or without treadmill may be due to the treadmill function moving the leg backward automatically without force generation during stance phase. Further, it would be possible that the displacement of the lower limb moves through less distance on treadmill walking than without treadmill in swing phase since human would be at the same position during treadmill walking. Although no previous research has clarified the biomechanical difference between walking with and without treadmill in water, researchers, exercise instructors and participants should pay attention to the differences of the muscle activity modality to determine more appropriate exercise and

Deep‐Water Running (DWR) is one of the unique exercise forms in water environment. Using a floatation device around the waist

Similar to the %MVC of lower limb muscle, the %MVC of hip and trunk muscles were also not as large during each walking style. The highest level of the %MVC in the hip and trunk muscles is around 20%. In addition to that, the mean differences in some muscles were very small, for example, the RA in both phase, the GMa and GMe in the swing phase. This should be taken into account for a more precise interpretation when applied to an actual exercise situation. Regardless of the fact, there are many noticeable changes when walking in water, compared with walking on land. Adductor Longus muscle appears to activate to stabilize pelvis and thigh segment [27, 28] during swing phase and does not fluctuate by water resistance force. Moreover, one of the important functions of AL is hip joint flexion matched to swing phase, during which relatively larger water resistance force added to lower limb. In respect to the stability during walking, GMe would act to increase stability of pelvis on the femur [28] against large water resistance force especially in the fast speed. Obliquus Externus Abdominis acts in body twisting yet the activity of OEA seems to decrease throughout walking in water compared with walking on land. Considering the results of the muscle activity, trunk twisting during water‐walking might be less than that during land‐walking. However, there is no evidence about movement in the transverse plane, and further research is needed to clarify this. Despite the fact that ES also acts in body twisting as well as OEA, the results showed higher activity in the ES during water‐walking than that during land‐walking. It is suggested that ES is compelled to activate against increased water resistance force on trunk during propulsion of the body. As evidence for this, the trunk forward inclination angle is larger during water‐walking than land‐walking (Figure 7), which is a counteractive

Figure 6. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during swing phase. [Modified from

\*

Figure 5. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during stance phase. [Modified from

LW WW

\*

%

AL GMa GMe RA OEA ES

Underwater Electromyogram for Human Health Exercise

\*

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\* \* \* \*

\*

%

AL GMa GMe RA OEA ES

\*

with increased frontal water resistance force.

Figure 7. Trunk inclination angle during walking. [Modified from reference 25]

\*: significant difference between water‐walking and land‐walking (P < 0.05)

\*: significant difference between water-walking and land-walking (P < 0.05)

**Figure 7.** Trunk inclination angle during walking. [Modified from reference 25]

specific prescription according to water‐walking style selected.

**4.1. Muscle activity in lower limb and trunk**

**4. The characteristics of muscle activity during deep‐water running**

(Figure 8), people move their feet as if running without touching the bottom of the swimming pool.

LW: land‐walking, WW: water‐walking

Positive: forward inclination Negative: backward inclination

LW: land-walking, WW: water-walking

Positive: forward inclination

Negative: backward inclination

reaction to deal with increased frontal water resistance force.

\*: significant difference between water‐walking and land‐walking (P < 0.05).

\* \* \*

AL GMa GMe RA OEA ES

\*: significant difference between water-walking and land-walking (P < 0.05).

\*

\*: significant difference between water‐walking and land‐walking (P < 0.05).

AL GMa GMe RA OEA ES

(A) (B)

AL GMa GMe RA OEA ES

(A) (B)

AL GMa GMe RA OEA ES

\* \*

\*

\*

\* \*

LW WW

LW: land‐walking, WW: water‐walking.

A: slow, B: moderate, C: fast.

%

LW: land-walking, WW: water-walking.

swing phase. [Modified from reference 25]

(C)

%

reference 25]

A: slow, B: moderate, C: fast.

reference 25]

A: slow, B: moderate, C: fast.

LW: land‐walking, WW: water‐walking.

%

(C)

%

\*: significant difference between water‐walking and land‐walking (P < 0.05). (A) (B) (C) 0 10 20 30 40 50 60 70 80 90 100 AL GMa GMe RA OEA ES % LW WW \* \* \* 0 10 20 30 40 50 60 70 80 90 100 AL GMa GMe RA OEA ES % \* \* \* \* \* 0 10 20 30 40 50 60 70 80 90 100 AL GMa GMe RA OEA ES % \* \* \* \* \* Similar to the %MVC of lower limb muscle, the %MVC of hip and trunk muscles were also not as large during each walking style. The highest level of the %MVC in the hip and trunk muscles is around 20%. In addition to that, the mean differences in some muscles were very small, for example, the RA in both phase, the GMa and GMe in the swing phase. This should be taken into account for a more precise interpretation when applied to an actual exercise situation. Regardless of the fact, there are many noticeable changes when walking in water, compared with walking on land. Adductor Longus muscle appears to activate to stabilize pelvis and thigh segment [27, 28] during swing phase and does not fluctuate by water resistance force. Moreover, one of the important functions of AL is hip joint flexion matched to swing phase, during which relatively larger water resistance force added to lower limb. In respect to the stability during walking, GMe would act to increase stability of pelvis on the femur [28] against large water resistance force especially in the fast speed. Obliquus Externus Abdominis acts in body twisting yet the activity of OEA seems to decrease throughout walking in water com‐ pared with walking on land. Considering the results of the muscle activity, trunk twisting during water-walking might be less than that during land-walking. However, there is no evidence about movement in the transverse plane, and further research is needed to clarify this. Despite the fact that ES also acts in body twisting as well as OEA, the results showed higher activity in the ES during water-walking than that during land-walking. It is suggested that ES is compelled to activate against increased water resistance force on trunk during

Figure 6. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during swing phase. [Modified from

AL GMa GMe RA OEA ES

\*

Figure 5. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during stance phase. [Modified from

\*

%

Similar to the %MVC of lower limb muscle, the %MVC of hip and trunk muscles were also not as large during each walking style. The highest level of the %MVC in the hip and trunk muscles is around 20%. In addition to that, the mean differences in some Figure 6. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during swing phase. [Modified from A: slow, B: moderate, C: fast.

reference 25]

A: slow, B: moderate, C: fast.

LW: land‐walking, WW: water‐walking.

%

(C)

%

\*: significant difference between water‐walking and land‐walking (P < 0.05).

AL GMa GMe RA OEA ES

(A) (B)

AL GMa GMe RA OEA ES

\*

\*

\* \*

LW WW

Figure 5. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during stance phase. [Modified from

**Figure 5.** The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during

Similar to the %MVC of lower limb muscle, the %MVC of hip and trunk muscles were also not as large during each walking style. The highest level of the %MVC in the hip and trunk muscles is around 20%. In addition to that, the mean differences in some muscles were very small, for example, the RA in both phase, the GMa and GMe in the swing phase. This should be taken into account for a more precise interpretation when applied to an actual exercise situation. Regardless of the fact, there are many noticeable changes when walking in water, compared with walking on land. Adductor Longus muscle appears to activate to stabilize pelvis and thigh segment [27, 28] during swing phase and does not fluctuate by water resistance force. Moreover, one of the important functions of AL is hip joint flexion matched to swing phase, during which relatively larger water resistance force added to lower limb. In respect to the stability during walking, GMe would act to increase stability of pelvis on the femur [28] against large water resistance force especially in the fast speed. Obliquus Externus Abdominis acts in body twisting yet the activity of OEA seems to decrease throughout walking in water com‐ pared with walking on land. Considering the results of the muscle activity, trunk twisting during water-walking might be less than that during land-walking. However, there is no evidence about movement in the transverse plane, and further research is needed to clarify this. Despite the fact that ES also acts in body twisting as well as OEA, the results showed higher activity in the ES during water-walking than that during land-walking. It is suggested that ES is compelled to activate against increased water resistance force on trunk during

LW WW

\*

%

AL GMa GMe RA OEA ES

\*

\* \* \* \*

\*

%

AL GMa GMe RA OEA ES

\*

Figure 6. The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during swing phase. [Modified from

\*

reference 25]

reference 25]

A: slow, B: moderate, C: fast.

A: slow, B: moderate, C: fast.

LW: land‐walking, WW: water‐walking.

A: slow, B: moderate, C: fast.

(C)

%

%

LW: land-walking, WW: water-walking.

stance phase. [Modified from reference 25]

%

(C)

%

220 Electrodiagnosis in New Frontiers of Clinical Research

\*: significant difference between water‐walking and land‐walking (P < 0.05).

AL GMa GMe RA OEA ES

(A) (B)

AL GMa GMe RA OEA ES

\*: significant difference between water-walking and land-walking (P < 0.05).

(A) (B)

AL GMa GMe RA OEA ES

AL GMa GMe RA OEA ES

\*

\* \* \*

\* \*

\*

\*

\* \*

LW WW

> muscles were very small, for example, the RA in both phase, the GMa and GMe in the swing phase. This should be taken into reference 25] LW: land-walking, WW: water-walking.

reaction to deal with increased frontal water resistance force.

account for a more precise interpretation when applied to an actual exercise situation. Regardless of the fact, there are many A: slow, B: moderate, C: fast. \*: significant difference between water-walking and land-walking (P < 0.05).

noticeable changes when walking in water, compared with walking on land. Adductor Longus muscle appears to activate to stabilize pelvis and thigh segment [27, 28] during swing phase and does not fluctuate by water resistance force. Moreover, one of the important functions of AL is hip joint flexion matched to swing phase, during which relatively larger water resistance force added to lower limb. In respect to the stability during walking, GMe would act to increase stability of pelvis on the femur [28] **Figure 6.** The mean ± standard deviation (SD) of %MVC value in each hip and trunk muscle at each speed during swing phase. [Modified from reference 25]

propulsion of the body. As evidence for this, the trunk forward inclination angle is larger during water-walking than land-walking (Figure 7), which is a counteractive reaction to deal with increased frontal water resistance force. against large water resistance force especially in the fast speed. Obliquus Externus Abdominis acts in body twisting yet the activity of OEA seems to decrease throughout walking in water compared with walking on land. Considering the results of the muscle activity, trunk twisting during water‐walking might be less than that during land‐walking. However, there is no evidence about movement in the transverse plane, and further research is needed to clarify this. Despite the fact that ES also acts in body twisting

as well as OEA, the results showed higher activity in the ES during water‐walking than that during land‐walking. It is suggested that ES is compelled to activate against increased water resistance force on trunk during propulsion of the body. As evidence for this, the trunk forward inclination angle is larger during water‐walking than land‐walking (Figure 7), which is a counteractive

Trunk muscles show different muscle activity between water and land based walking, as well as lower limb. However, when humans walk on a treadmill apparatus, most muscle activity decreased during water compared with land in both lower limb and trunk area [29]. In this case, the walking speed was set as one‐half to one‐third of the land walking in reference to the oxygen consumption [17]. Furthermore, muscle activity during treadmill water‐walking without water flow further decreased muscle activity than with flow set to the same speed to the walking speed [29]. The differences between with or without treadmill may be due to the treadmill function moving the leg backward automatically without force generation during stance phase. Further, it would be possible that the displacement of the lower limb moves through less distance on treadmill walking than without treadmill in swing phase since human would be at the same position during treadmill walking. Although no previous research has clarified the biomechanical difference between walking with and without treadmill in water, researchers, exercise instructors and participants should pay attention to the differences of the muscle activity modality to determine more appropriate exercise and

Deep‐Water Running (DWR) is one of the unique exercise forms in water environment. Using a floatation device around the waist

Figure 7. Trunk inclination angle during walking. [Modified from reference 25] LW: land‐walking, WW: water‐walking LW: land-walking, WW: water-walking \*: significant difference between water-walking and land-walking (P < 0.05) Positive: forward inclination Negative: backward inclination

\*: significant difference between water‐walking and land‐walking (P < 0.05)

specific prescription according to water‐walking style selected.

**4.1. Muscle activity in lower limb and trunk**

Positive: forward inclination

Negative: backward inclination

**Figure 7.** Trunk inclination angle during walking. [Modified from reference 25]

**4. The characteristics of muscle activity during deep‐water running**

(Figure 8), people move their feet as if running without touching the bottom of the swimming pool.

Trunk muscles show different muscle activity between water and land based walking, as well as lower limb. However, when humans walk on a treadmill apparatus, most muscle activity decreased during water compared with land in both lower limb and trunk area [29]. In this case, the walking speed was set as one-half to one-third of the land walking in reference to the oxygen consumption [17]. Furthermore, muscle activity during treadmill water-walking without water flow further decreased muscle activity than with flow set to the same speed to the walking speed [29]. The differences between with or without treadmill may be due to the treadmill function moving the leg backward automatically without force generation during stance phase. Further, it would be possible that the displacement of the lower limb moves through less distance on treadmill walking than without treadmill in swing phase since human would be at the same position during treadmill walking. Although no previous research has clarified the biomechanical difference between walking with and without treadmill in water, researchers, exercise instructors and participants should pay attention to the differences of the muscle activity modality to determine more appropriate exercise and specific prescription according to water-walking style selected.

swing phase in walking exercise, respectively. One-way repeated measures analysis of variance (ANOVA) with Tukey's post-hoc test was applied for the statistic comparison.

(B)

)

0000000000TA SOL

\* \* \* \* \*

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± SD of %MVC ate, C: fast.

\*: significant difference (P < 0.05).

[Modified from reference [11]

%

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SOL GAS

LW: land-walking, WW: water-walking, DWR: Deep-Water Running

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VL BF

\* \*

GAS RF

BF

\* \*

er Running

**Figure 9.** The mean ± SD of %MVC value in each lower limb muscle at each speed during backward swing phase.

As seen in Figure 9 and 10, the characteristics of the DWR, %MVC of the SOL, GAS in the backward swing phase, and the VL in the forward swing phase were dramatically de‐ creased compared with water- and land-walking (P<0.05). This is likely a result of the noncontact phase during DWR compared to land walking. On the other hand, %MVC of the BF in both swing phases, and the RF in forward swing phase were much higher than land- and sometimes water-walking (P<0.05). The knee and hip joint range of motion (ROM) was increased during DWR when comparedto both land- and water-walking (Figure 12), which would cause the higher %MVC in the RF and BF. Similarly this increased ROM of the hip would also result in higher %MVC of the GMa, AL and GMe during the DWR than during water- and land-walking. Increased ROM directly indicates that thigh and knee extension and flexion muscles receive greater water resistance force. Further, it is likely that the AL and GMe activated to stabilize the pelvis against femur during an unstable floating situation as

Interestingly, the %MVC of the RA, OEA and ES were higher during DWR than water- and land-walking throughout one-cycle (P<0.05, Figure 11). The authors speculated that maintain‐ ing forward inclination during DWR would increase the RA and OEA muscles activation

RF VL

RF VL

BF

\* \*

LW WW DWR

R: Deep‐Wate

walking, DWR

\*

(C)

%

TA

SOL GAS

\* \*

\* \* \*

\* \*

\*

\* \* \*

g, WW: water‐w rence (P < 0.05
