**2.1. The methodology for the collection of muscle activity in underwater environment**

Measuring muscle activity by EMG method is challenging because most EMG devices are not waterproofed. As with all electronic devices, water immersion can be dangerous. Because of this risk, most research has used silver-silver-chloride surface EMG electrodes as passive surface electrodes [10, 11]. Some researchers who have investigated muscle activity using EMG devices developed their own waterproofing methods [10, 11] of which there are two types. The first type attached a waterproof seal onto the electrodes placed on the local muscle of interest [10, 11], and the second wears a dry suit on the whole body created for EMG collection [10, 12].

Waterproofing the seal onto the electrodes usually involves attaching transparent film and/or a foam pad (Foam Pad, 75A: Nihon Kohden, Tokyo, Japan) and this method has been used successfully in previous research [10, 11]. For even better waterproofing, transparent film and/ or foam pad are attached in combination [10, 11]. This is achieved by sealing a small piece of transparent film over the electrodes which are attached on the muscle belly to be studied. Then, fill up the slight gap between electrodes leads and transparent film with putty. Finally, use a large piece of transparent film to cover over the small size film and putty (Figure 1).

A: doubled by transparent films with putty. B: covered by foam pad.

73.5mmHg [1], which is similar to normal diastolic blood pressure. Hydrostatic pressure causes blood to shift from the lower extremities to the thoracic region [5], and also affects lung, renal and other endocrine functions [6]. Thermal conductivity, which is about 25 times faster than air, also affects the human circulatory system [1]. When a human is immersed in water with a lower than thermo-neutral temperature, peripheral vasoconstriction occurs and increases the blood shift to the thoracic region [7]. This thermoregulation effect has been used

As briefly described above, the water physical qualities can be very beneficial for the human body. In addition to those effects, exercising in a water environment is a safe environment and may reduce the incidence of falling [8]. A wide range of people including those who have difficultymovingonlandduetoobesity,alower-limbdisorder,throughtothosewhoarehealthy or want to improve their fitness may benefit from utilizing the water environment [8, 9].

**1.2. Why knowledge of muscle activity during exercise in a water environment is important?** When exercising in water, the benefits of buoyancy and water resistance mainly occur be‐ cause these qualities act directly on the exercise motion. For example, weight reduction, due to buoyancy,maycontributetotheupwardordownwardmotion,andadditionalloadingbywater resistance would strongly affect the motion in any direction. Therefore, the instructors of water exercise need to consider the effect of water specific qualities can play on the human body.

As a method of understanding the loading or offloading effect of water specific qualities on human body, investigation of muscle activity is considered an important tool. This provides information regarding the degree of muscle loading during exercise in water, and also provides a basis to apply health and rehabilitation exercise in a water environment more effectively. It is easily hypothesized that the muscle activity would be changed during exercise in water, compared with the same exercise on land. However, there is a challenge in measuring muscle

In consideration of these points, firstly, this chapter focuses on the methodology and its validity of collecting muscle activity data in a water environment, with special mention regarding a waterproofing method. Following this, the muscle activity modality for walking, running and many other exercise forms in water are also featured. Walking and running exercise in water are the most popular and basic exercise forms of water exercise [9]. This chapter focuses on walking, running and other water exercise forms which is based on gait, for example, walking with long step, walking with twisting, walking with kicking and so on. Finally, this chapter

provides an informative suggestion for exercise participants and instructors.

**2.1. The methodology for the collection of muscle activity in underwater environment**

Measuring muscle activity by EMG method is challenging because most EMG devices are not waterproofed. As with all electronic devices, water immersion can be dangerous. Because of

**2. How to collect underwater electromyogram (EMG)?**

for a range of therapeutic practices [1].

214 Electrodiagnosis in New Frontiers of Clinical Research

activity in a water environment.

**Figure 1.** Waterproofing of surface electrodes. [Pictures were taken by the authors]

Even when this strict waterproofing is applied the water can sometimes immerse under the films cause interference with the electrodes. Therefore, when using this method, the EMG signal has to be monitored continuously throughout the experiment to ensure the data is not affected by water intrusion. When water intrusion under the films or electrodes occurs, a high frequency noise and/or baseline fluctuation on the wave data would be observed. If an abnormal data reading is confirmed due to water intrusion, the electrodes attachment has to be removed and re-applied and the experiment procedure should be started over again. In addition to the waterproofing to the electrodes, the code of each electrode should be taped along with body segment to avoid unexpected tension by water resistance and swinging by exercise motion in water which may prevent or interfere with the normal motion (Figure 2). Due to the series of extensive electrode attachments, waterproofing procedures and establish‐ ing the settings for collecting data of underwater EMG, the procedure for underwater EMG takes considerably longer to perform compared with testing in the land environment.

A whole body dry suit has been developed for the collection of underwater EMG, specifically for water sports activities to allow full range of motion [10, 12]. This suit consists of waterproof material with the arm, leg and neck openings tightly sealed. Once the electrodes are attached on the subject, the electrodes and its leads are well covered from the water due to the fully enclosed suit. The advantages of this suit include less set up time than waterproofing and

recording by waterproofing in water exercise suggesting future EMG studies should conduct MVC testing in water for data normalization and confirm the post-exercise verification of EMG recording. It can be then assumed due to the body of previous research that the collection of EMG data during water environment is not influenced by water immersion if the electrodes were waterproofed, however, it might be more reliable to verify post-experiment EMG

Underwater Electromyogram for Human Health Exercise

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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

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

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

conditions. Figure 3 and Figure 4 showed the result of the study.

recordings and/or normalization in water MVC.

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

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

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 water intrusion at the openings [10, 12].

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

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 recording by waterproofing in water exercise suggesting future EMG studies should conduct MVC testing in water for data normalization and confirm the post-exercise verification of EMG recording. It can be then assumed due to the body of previous research that the collection of EMG data during water environment is not influenced by water immersion if the electrodes were waterproofed, however, it might be more reliable to verify post-experiment EMG recordings and/or normalization in water MVC.
