**4. Assessment of relative proprioceptive weighting ratio in elderly people with lumbar spondylosis**

#### **4.1. Sensory proprioceptive inputs in postural control**

In daily life, an upright postural control task is essential for the activities of elderly people. After processing of the sensory inputs, individuals must integrate the respective contribu‐ tions of the various sources of sensory information for regulating posture. Hay et al. reported that older persons have difficulties in taking advantage of sensory redundancy in postural control [31]. In addition, a defect or slowing of this mechanism has been suggested to explain the difficulties experienced by older persons when trying to control their posture [32, 33]. Proprioceptive input from the muscles of the legs and trunk plays an important role in main‐ taining postural stability [34]. Previous studies have reported that proprioception and vibra‐ tion sensation in the lower limbs decrease during normal aging [3, 4] and also reported that postural instability has been observed in elderly people [35]. Therefore, a vibratory stimulus that matches the response frequency of the receptors present in skeletal muscle may influence body sway (**Figure 6**).

*3.1.5. Appendicular skeletal muscle mass assessment*

*3.1.6. Prediction models*

32 Clinical Physical Therapy

(*R*<sup>2</sup>

 = 0.87).

0.881 (*R*<sup>2</sup>

cumference ‐ 0.011 × Age + 5.135 (*R*<sup>2</sup>

 waist circumference + 2.747 (*R*<sup>2</sup>

 = 0.89).

**3.2. Reduced physical activity**

**with lumbar spondylosis**

equations for estimating skeletal muscle mass [24–26].

**Sanada K, et al., 2010: Prediction models of sarcopenia [24]**

**Yoshida D, et al., 2014: Bioelectrical impedance analysis [25]**

+ 0.168 × (maximum calf circumference) − 0.815 (*R*<sup>2</sup>

**4.1. Sensory proprioceptive inputs in postural control**

In the elderly, muscle weakness is associated with the muscle atrophy aging (sarcopenia) pro‐ gressive loss. Skeletal muscle mass loss may also have the potential to impact quality of life and ultimately the need for long‐term care in elderly people [23]. Several studies developed

Men: appendicular skeletal muscle mass = 0.326 × body mass index (BMI) − 0.047 × waist cir‐

Women: appendicular skeletal muscle mass = 0.156 × BMI + 0.044 × hand grip strength − 0.010 ×

Men: appendicular skeletal muscle mass = 0.197 × (impedance index) + 0.179 × (weight) 0.019

Women: appendicular skeletal muscle mass = 0.221 × (impedance index) + 0.117 × (weight) + 

Appendicular skeletal muscle mass = 5.051 × (gender: men = 1, women = 0) + 0.364 × (BMI) 

Past studies have provided the first evidence that slightly constricted life space may serve as an important marker and/or risk factor for the development of frailty, whereas severely constricted life space may indicate a high risk of mortality [27]. Webber et al. reported how mobility impairments can lead to limitations in accessing different life spaces and stressed the associations among determinants that influence mobility [28]. Previous study reported falls

**4. Assessment of relative proprioceptive weighting ratio in elderly people** 

In daily life, an upright postural control task is essential for the activities of elderly people. After processing of the sensory inputs, individuals must integrate the respective contribu‐ tions of the various sources of sensory information for regulating posture. Hay et al. reported

 = 0.80).

 = 0.68).

 = 0.57).

**Ito T, et al., 2016: Simple estimation of appendicular muscle mass [26]**

and reduced life space closely related to physical performance [29, 30].

Previous studies have reported that patients with recurrent low back pain (LBP) have impaired motor control [36] and altered lumbosacral proprioceptive acuity [37, 38]. LBP is a widespread pathological condition that is often related to impaired or degenerated trunk mobility, which becomes evident during common activities [39, 40]. Taimela et al. reported that lumbar muscle fatigue impaired lumbar positional sense in both patients with LBP and healthy subjects [41]. These impairments lead to pain and declines in postural strategy, muscle function, and pro‐ prioception [42, 43].

**Figure 6.** The representative receptor and response frequencies are 30 Hz in Meissner's corpuscles, 60 Hz in muscle spindles, and 240 Hz in Vater‐Pacini corpuscles.

Muscle vibration, known to be a strong stimulus for muscle spindles and Vater‐Pacini corpus‐ cles, has been used to assess the role of proprioception [44, 45]. Both of these studies suggest that pain is a possible cause of decreased variability in postural strategy. These impairments lead to pain and declines in postural strategy, muscle function, and proprioception.

### **4.2. Assessment of relative proprioceptive weighting ratio**

The center of pressure (COP) was recorded using a balance board (Wii; Nintendo Co., Ltd., Kyoto, Japan) (**Figure 7**) [46–48]. A vibratory stimulus is applied alternately to each muscle by fixing vibrators from the vibration device onto the subjects' lumbar multifidus (LM) muscle and gastrocnemius (GS). The device consists of an amplifier, laptop computer, and four vibra‐ tors (**Figure 8**). This mechanical vibration test has been used to analyze the role of propriocep‐ tion in the postural control strategy [49–53].

The subjects stood barefoot on the Wii Balance Board with their feet together and their eyes closed. They were instructed to remain still and relax in the standing posture with their arms hanging loosely at their sides (**Figure 9**).

To provide information regarding relative proprioceptive sensation dominance, the relative proprioceptive weighting (RPW) ratio was calculated using following computation expression.

$$\text{RPW} = \text{(Abs GS)} / \text{(Abs LM + Abs GS)} \times 100 \text{[\%]}$$

RPW of near to 0 conform to 100 [%] dependence on trunk strategy, whereas RPW of near to 100 conform to 100 [%] dependence on lower limb strategy [54–56].

**Figure 7.** Recently, the Wii Balance Board has been much used in the field of medical research, and it has been reported that results from the Wii Balance Board correlate closely with those of commercially available force plates.

**Figure 8.** Photograph and block diagram of variable‐frequency vibratory stimulation device.

Muscle vibration, known to be a strong stimulus for muscle spindles and Vater‐Pacini corpus‐ cles, has been used to assess the role of proprioception [44, 45]. Both of these studies suggest that pain is a possible cause of decreased variability in postural strategy. These impairments

The center of pressure (COP) was recorded using a balance board (Wii; Nintendo Co., Ltd., Kyoto, Japan) (**Figure 7**) [46–48]. A vibratory stimulus is applied alternately to each muscle by fixing vibrators from the vibration device onto the subjects' lumbar multifidus (LM) muscle and gastrocnemius (GS). The device consists of an amplifier, laptop computer, and four vibra‐ tors (**Figure 8**). This mechanical vibration test has been used to analyze the role of propriocep‐

The subjects stood barefoot on the Wii Balance Board with their feet together and their eyes closed. They were instructed to remain still and relax in the standing posture with their arms

To provide information regarding relative proprioceptive sensation dominance, the relative proprioceptive weighting (RPW) ratio was calculated using following computation expression.

RPW of near to 0 conform to 100 [%] dependence on trunk strategy, whereas RPW of near to

**Figure 7.** Recently, the Wii Balance Board has been much used in the field of medical research, and it has been reported

that results from the Wii Balance Board correlate closely with those of commercially available force plates.

*RPW* = (*Abs GS*)/(*Abs LM* + *Abs GS*) × 100[%]

100 conform to 100 [%] dependence on lower limb strategy [54–56].

lead to pain and declines in postural strategy, muscle function, and proprioception.

**4.2. Assessment of relative proprioceptive weighting ratio**

tion in the postural control strategy [49–53].

34 Clinical Physical Therapy

hanging loosely at their sides (**Figure 9**).

**Figure 9.** Experimental setup: paraspinal muscles and gastrocnemius muscles in vibration trial.

#### **4.3. Proprioceptive input decline from the muscles of the legs or trunk**

Recent studies in which a vibratory stimulation of 60 Hz was used have suggested that peo‐ ple with LBP adopt a lower leg‐derived postural control strategy [57]. A possible explanation is that these participants were exploiting this strategy to its maximum effect during vibra‐ tory stimulation of 60 Hz. Also, according to other study, the impairment of back muscle strength leads to the motor function and sensory deficit that affects balance performance [58]. Moreover, according to another study, the lower leg's response to balance control under 30 Hz proprioceptive stimulation might be a good indicator of declining gait function [59].

These differences may result from differences between the measurement conditions and physical status of the participants.
