To investigate the effect of gastrocnemius muscle fatigue on postural control ability in elderly people.
Twenty-four healthy elderly people participated in this study. The postural control ability of single leg standing was evaluated with Health Improvement & Management System (HIMS) posturography before and after fatiguing exercises. After evaluating initial postural control ability, the maximal voluntary contraction (MVC) of ankle plantarflexion was assessed using a surface electromyogram from the medial belly of the gastrocnemius muscle. After a 5-minute resting period, subjects began submaximal isometric ankle plantarflexion (40% MVC) until 40% of MVC was dropped below 95% for 5 seconds, or subject couldn't continue working out due to muscle fatigue. And postural control ability was assessed after fatiguing exercise. The mean deviation of center of pressure (COP), length of COP movement, occupied area of COP were measured, and analyzed by paired t-test.
Mediolateral deviation, length of COP movement, and area of COP occupied were increased after fatiguing exercise of the gastrocnemius muscle. Anteroposterior deviation and length of COP movement were also increased, but had low statistical significance.
These findings suggest that the gastrocnemius muscle fatigue affects mediolateral stability and accuracy during single leg standing in elderly people. Therefore muscle endurance training is necessary to prevent falls in elderly people.
Falls in the elderly are a very common and severe problem. As of 2010, the population of elderly aged over 65 years in Korea reached 11% of the total population [
Postural control is the ability that is necessary to safely perform walking and daily activities and is closely related to falls. Both neurological and musculoskeletal factors are complexly involved in postural control. Neurological factors include central processing and neural pathways for motor control after sensory organs, such as the visual, vestibular and proprioceptive organs, receive some information related to imbalance [
Motor signals recover various imbalance conditions whether it is predictable or not [
Understanding the effects of plantarflexor muscle fatigue on balance control may be helpful for preventing falls that can occur during daily living activities. Yaggie and McGregor [
This study, therefore, investigates the effects of plantarflexor muscle fatigue on postural control by inducing muscle fatigue with submaximal isometric plantarflexion in normal elderly subjects.
The subjects of this study include 24 healthy elderly over 65 years (17 men, 7 women) who perform daily activities independently (
Before starting this study, an approval from the Institutional Review Board was granted. Subjects included the elderly who had participated in individual interviews and consented after being given a full description of the objective of the study and testing.
The relationship between muscle fatigue and postural control was evaluated by measuring balance control with Health Improvement & Management System (HIMS; The HIMS Inc., Suwon, Korea) posturography before and after fatiguing exercise. For the balance control test, subjects were asked to place one bare foot on the center of a force plate, keeping their eyes straight and putting both hands on their waists in a quiet room with little external stimulation (
QEMG-4 surface electromyogram (Laxtha, Daejeon, Korea) equipped with a 4-channel recording unit was used to evaluate plantarflexor muscle fatigue. The measurement was sampled at the rate of 1,024 Hz, with the frequency set and recorded between 10-2,000 Hz. As for the amplified electromyogram signal, the mean of the root mean square (RMS) was measured after the processes of full wave rectification and 20 Hz high pass filter with the EMG Works program (Laxtha, Daejeon, Korea) [
After 5 minutes of warm-up exercises and stretching, subjects sat on a chair with the hip flexed at 80°-90°, knee and ankle positioned at 0°, trunk and thighs fixed, and then practiced isometric plantarflexion exercises (
After the warm-up exercise and preparation for surface electromyogram, a test for maximal voluntary contraction (MVC) of the plantarflexor was performed. Without any contraction on the shoulders, trunk, and thighs during the test, three 3-second maximal isometric plantarflexions were performed. A 5-second rest was given between each contraction. The exercise was performed from the left leg to the right. Of the MVC values of both gastrocnemius muscles obtained by the exercises, the maximum RMS value each was defined as 100% muscle activity, 40% of which was set as a criterion for fatiguing exercise (40% MVC) [
The method of Nordez et al. [
In order to analyze the difference of balance control before and after muscle fatigue, mean deviation, length and area of the center of pressure (COP) were used (
SPSS ver. 12.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. All data obtained to examine the change of postural control ability before and after muscle fatigue were described by mean and standard deviation to identify their patterns. The difference of the variables in each group was analyzed by paired t-test. A p-value<0.05 was considered statistically significant.
The mediolateral and anteroposterior deviations of the subjects' bodies were assessed by analyzing the mean of the COP position toward the x-axis (deviation X) and y-axis (deviation Y) (
The change in the accuracy of the postural control before and after fatiguing exercise was assessed by analyzing the occupied area of COP with the indices of envelope area (EVAR) and root mean square area (RSAR) (
Length indicates the length of COP movement toward all directions during the balance test, including the mediolateral and anteroposterior directions, and can be used to evaluate postural sway and the efficiency of postural control ability (
The prevalence of sarcopenia is 30% in the elderly aged over 65 years and 50% in those aged over 80 years [
Plantarflexion is controlled primarily by the gastrocnemius and soleus muscles, and partly by the plantaris muscle, flexor hallucis longus muscle, flexor digitorum longus muscle, peroneus muscle, and tibialis posterior muscle [
In the present study, if fatigue was induced to plantarflexor muscles, the mean COP showed more anteroposterior deviation and postural sway became larger, but no statistical significance was found. This finding can be attributed to the fact that compromised balance due to fatigued plantarflexor was compensated by the recruitment of alternate motor unit [
In this study, the degree of mediolaterally displacement of COP and postural sway increased, showing a statistically significant correlation. This appears to be due to the fact that when performing plantarflexion to induce fatigue, fatigue was also induced to the peroneus muscle, which involves plantarflexion as well, as it was co-contracted with the gastrocnemius [
The area occupied by COP has a lower value as postural control is more accurately performed [
The weakness of plantarflexor muscle endurance in the elderly due to sarcopenia is a risk factor associated with reduced balance control [
Controlling plantarflexion is important for safely performing activities of daily living for the elderly. If the muscles around the ankle get easily fatigued due to reduced muscle endurance, the control of exercise becomes difficult, readily exposing them to the risk of falls [
This study has a few limitations. First, since the number of subjects was not large and the test was performed for elderly aged over 65 years, there is a limitation for the results of this study to be applied to the elderly in various age groups. Second, this study cannot fully reflect the dynamic balance changes, such as standing and walking, because it evaluated the balance in a static condition. Finally, the hip adductors/abductors, in addition to the plantarflexor, can affect the mediolateral balance control. Further studies considering these limitations need to be conducted.
In conclusion, for daily activities of normal elderly, submaximal isometric plantarflexion, which is closely associated with muscle endurance, is important. The findings of this study show that the muscle fatigue induced by plantarflexion reduces the ability and accuracy of mediolateral postural control. This suggests that when prescribing exercises to prevent falls in the elderly, a combination of resistance exercises and exercises to improve the muscle endurance around the ankle is effective.
No potential conflict of interest relevant to this article was reported.
Postural control ability of single leg standing evaluated with Health Improvement & Management System (HIMS) posturography.
Posture of isometric ankle plantarflexion.
Subjects undertook fatiguing exercises consisting of warm-up exercise (W), maximal voluntary contraction (MVC) with some contractions (C) and rests (R), submaximal isometric contraction, and end of test (E).
Center of pressure (COP) motion was assessed by deviations X and Y, area of COP, and length of COP.
Example of posturography results.
General characteristics of subjects
Values are presented as number or mean±standard deviation.
Comparison of deviations X and Y, areas, lengths in pre-exercise and post-exercise
Values are presented as mean±standard deviation.
*p<0.05.