Aging-Related Changes in Muscle Strength: A Comparison Between Young and Elderly Individuals

Yusuke Chigira; Yoichi Ohno; Nobuyuki Takeuchi; Takahiro Oda

doi:10.26644/em.2025.001

Abstract

Objectives:

Few studies have investigated aging-related changes in muscle strength. The purpose of this study is to measure muscle strength in young and elderly individuals to clarify the differences in aging-related muscle weakness across various muscles.

Methods:

The subjects consisted of 43 healthy young persons (20.33±0.47 years, 16 males, 27 females) and 38 elderly residents with independent activities of daily living (ADL) (78.34±7.67 years, 18 males, 20 females). Maximal isometric force, measured using a hand-held dynamometer, was expressed as force (N) divided by the body weight (N/kg), and compared between the young and elderly subjects. Furthermore, the elderly subjects’ value (older-to-young ratio (O-Y ratio)) was calculated establishing the mean muscle strength in the young subjects as a reference (100%). The characteristics of aging-related changes were also examined.

Results:

There were significant differences in muscle strength between the young and elderly subjects for ankle dorsiflexion, knee flexion/extension, hip flexion/extension, shoulder flexion/abduction/internal rotation/external rotation, and elbow flexion. The O-Y ratio for hip extension was the lowest, followed by shoulder external rotation, shoulder internal rotation, shoulder flexion, and hip flexion.

Conclusions:

Concerning aging-related muscle weakness, that of hip extension was particularly marked. To strengthen ADL motions/physical endurance, the understanding of muscle groups that decrease with aging may be important.

Keywords: aging-related muscle weakness; anti-aging training; elderly; muscle strength

INTRODUCTION

Physical frailty in the elderly is functional impairment derived from natural aging-related motor hypofunction, especially sarcopenia. In Japan, the number of elderly persons is approximately 35,890,000, and the proportion of the elderly population exceeds 28.4% (2019). It is estimated that population aging will reach a peak in 2025, and that the proportion of the elderly population will continue to be high until 2050 [1].

As the number of elderly persons requiring nursing care increases, high-quality comprehensive support due to decreased performance or quality of life (QOL) is important. In most elderly persons requiring nursing care, the cause is not a specific disorder but aging-related psychosomatic hypofunction termed “geriatric syndrome”. Frailty, falling/fracture, and articular disorder result from a decline in locomotor function or motor abilities. Thus, exercise therapy that improves locomotor function may be effective [2].

Concerning strength training in the elderly, its efficacy was confirmed in the 1990’s, and its evidence level is high [3]. To perform exercise therapy in the elderly, it is necessary to understand aging-related body composition/physiological changes and promote this therapy safely and efficiently. However, their physical characteristics remain to be clarified for performing exercise therapy.

A study on aging-related changes reported that lower-extremity muscle strength, especially knee extension muscle strength, in persons aged 80 to 89 years is approximately 1/2 to 1/3 of that in those aged 20 to 29 years [2]. Factors involved in decreased lower-extremity muscle mass in elderly persons may include a decline in activities of daily living (ADL) and less retirement-related physical activities. In addition, the influence of activity restrictions may be associated with aging-related diseases. Thus, clarifying the characteristics or differences with respect to muscle groups and mass other than the muscle strength of the lower extremities with a marked decrease in the muscle mass is needed. Few studies have investigated aging-related changes in general muscle strength.

The purpose of this study was to measure lower-/upper-extremity muscle strength, which may influence ADL, in elderly and young persons and clarify elderly persons’ physical characteristics for future exercise therapy..

METHODS

Study participants

The subjects consisted of 43 healthy young persons (20.3±0.47 years, 16 males, 27 females) and 38 elderly residents with independent ADL (78.3±7.8 years, 18 males, 20 females) in whom muscle strength was measured between September 2022 and March 2023. Exclusion criteria included persons with dementia and those with orthopedic or respiratory/cardiovascular diseases.

The sample size was calculated using G*Power 3.1.9.7 (Heinrich Heine University of Duesseldorf, Duesseldorf, Germany). For the calculation of the sample size, an effect size of 0.5, significance level of 0.05, and power of 80% were used. The number of participants was calculated as 67 per group. Participants were recruited, and 43 young and 38 elderly participants were finally enrolled in reference to the exclusion criteria.

Maximal isometric force and muscle strength

The maximal isometric force (N) of two measurements of the dominant hand and foot was measured using a handheld dynamometer (MOBIE MT-100: SAKAI Medical Co., Ltd.) and divided by the body weight (N/kg). The measurements were conducted by a single experienced evaluator to ensure consistency and eliminate variations caused by differences between evaluators. Regarding the mean muscle strength in the young subjects as a reference (100%), the elderly subjects’ value (old-to-young ratio: O-Y ratio) was calculated to examine aging-related changes.

Concerning measurement methods (Figure 1), muscle strength on ankle plantar flexion (a) was measured as follows: each subject was placed in a prone position on the bed, and instructed to put the dominant foot out of the bed end and do ankle plantar flexion. Resistance was applied to the plantar area of the metacarpophalangeal (MP) joint for measurement. Muscle strength on ankle dorsiflexion (b) was measured by instructing each subject to do ankle dorsiflexion in a sitting position and applying resistance to the dorsum-of-foot area of the MP joint.

Muscle strength on knee flexion (c) was measured as follows: each subject was instructed to put the hands on the posterior area in a sitting position and flex the knees at 90 degrees. Resistance was applied to a 1/4 distal part on the posterior surface of a lower leg for measurement.

Muscle strength on knee extension (d) was measured as follows: each subject was instructed to put the hands on the posterior area in a sitting position and flex the knees at 90 degrees. Resistance was applied to a 1/4 distal part on the anterior surface of a lower leg for measurement.

Muscle strength on hip flexion (e) was measured by instructing each subject to flex the hip in a sitting position and applying resistance to a 1/4 distal part on the anterior surface of the thigh. Muscle strength on hip extension (f) was measured as follows: each subject was instructed to bend the trunk forward to approximately 45 degrees of hip flexion in a standing position and extend the hip of a leg on the measurement side so that it may be aligned with the trunk. Resistance was applied to a 1/4 distal part on the posterior surface of the thigh for measurement.

Muscle strength on hip abduction (g) was measured as follows: each subject was instructed to abduct the hip of an upper-side leg in a side position at 30 degrees. Resistance was applied to a 1/4 distal part on the lateral surface of the thigh for measurement.

Muscle strength on hip adduction (h) was measured as follows: each subject was instructed to adduct the hip of a lower-side leg in a side position at 15 degrees. Resistance was applied to a 1/4 distal part on the medial surface of the thigh for measurement.

Muscle strength on shoulder flexion (i) was measured by instructing each subject to flex a shoulder in a sitting position and applying resistance to a 1/4 distal part on the superior surface of the upper arm.

Muscle strength on shoulder abduction (j) was measured by instructing each subject to abduct a shoulder in a sitting position and applying resistance to a 1/4 distal part on the superior surface of the upper arm.

Muscle strength on shoulder external rotation (k) was measured as follows: each subject was placed in a prone position on the bed, and instructed to externally rotate a shoulder to a final range of motion at the 90-degree shoulder abduction position. Resistance was applied to a 1/4 distal part on the dorsal side of the forearm for measurement.

Muscle strength on shoulder internal rotation (l) was measured as follows: each subject was placed in a prone position on the bed, and instructed to internally rotate a shoulder to a final range of motion at the 90-degree shoulder abduction position. Resistance was applied to a 1/4 distal part on the palmar side of the forearm for measurement.

Muscle strength on elbow flexion (m) was measured by instructing each subject to flex an elbow to a final range of motion in a sitting position and applying resistance to a 1/4 distal part on the palmar side of the forearm.

Statistical Analysis

For statistical analysis, the Shapiro-Wilk test was used to compare the muscle strength data between the young and elderly subjects. As there was no normality in a portion of the data, the Mann-Whitney U-test was performed. We used SPSS Statistics software (version 17.0, IBM, U.S.A.). A p-value of 0.05 was regarded as significant.

The effect size of a difference in the mean value between the two groups was calculated using Cohen’s d. Concerning the effect size, a value of 0.20 to 0.49 was regarded as low effects, a value of 0.50 to 0.79 as moderate effects, and a value of ≥0.80 as high effects.

Prior to this study, its protocol was approved by the ethics review board of Kan-etsu Chuoh Hospital (Approval No.: 20220424). For participation in this study, the study contents were explained to the subjects in accordance with the Helsinki Declaration, and informed consent regarding participation was obtained.

RESULTS

Comparison of muscle strength between the young and elderly subjects revealed significant differences in ankle dorsiflexion, knee flexion/extension, hip flexion/extension, shoulder flexion/abduction/external rotation/internal rotation, and elbow flexion (Table 1).

The effect sizes of ankle plantar flexion and hip abduction/adduction, with no significant difference in muscle strength, were low.

In the elderly, the O-Y ratio for hip extension (55.9726.01%) was the lowest, followed by shoulder external rotation (69.89±30.63%), shoulder internal rotation (70.62±28.52%), shoulder flexion (74.63±28.60%), and hip flexion (76.71±25.16%) (Table 2) (Figure 2).

DISCUSSION

In this study, maximum muscle strength was defined as maximum force divided by the body weight (N/kg), because we considered it important to present the muscle strength using the muscle strength/body weight ratio for the confirmation of aging-related changes, excluding the influence of the body weight, with respect to sex difference. Previous studies [4,5] also reported that there was no sex difference when the muscle strength value was presented with the muscle strength/body weight ratio. Concerning sex difference, the muscle strength is generally greater in males, but we considered it the most important to present the muscle strength using the muscle strength/body weight ratio, excluding the influence of the body weight, for reviewing aging-related changes, and adopted it in this study.

Aging-related decreases in the muscle mass or strength in lower extremity muscles is reportedly more marked than in upper extremity muscles [6]. In this study presenting the muscle strength value using the muscle strength/body weight ratio, such a reduction was also the most marked on hip extension. However, muscle strength on shoulder external rotation, shoulder internal rotation, and shoulder flexion was also markedly reduced, confirming that the influence of aging is more marked around major joints, such as the hip and shoulder.

Studies regarding aging-related changes in physical ability [7,8] reported that quadriceps muscle strength was strongly associated with physical ability (the ability to go up and down stairs, balance), suggesting its importance. Many studies on quadriceps muscle strength showed that it reached a peak at 20 years of age, then decreasing from 40 to 49 years of age [9,10]. This study also compared the muscle strength (muscle strength/body weight ratio) between the young (20 to 29 years of age) and elderly (approximately 80 years of age) subjects, and demonstrated muscle weakness in the latter. Among other muscle groups investigated in this study, muscle strength was relatively maintained. However, due to major anti-gravity muscles, it may be important to maintain/strengthen these muscle groups. Among lower extremity muscles, there was no significant difference in the ankle plantar flexor, suggesting that muscle strength is relatively maintained even in elderly persons. It is maintained in elderly persons with independent ADL possibly because this muscle is the closest to the ground to support the body weight. As the reason why aging-related hip extensor muscle weakness was marked, posterior pelvic tilt due to aging-related postural changes in elderly persons may have decreased the hip extension range of motion during walking, contributing to hip extensor muscle weakness.

Hip extension is not only essential for walking but also plays a critical role in fall prevention and activities such as sitting and standing up [11]. In elderly individuals, the range of motion and strength of hip extension are particularly important for the execution of activities of daily living (ADL) and walking [12], highlighting the need to maintain its functionality.

In addition to bridging exercises performed in the supine position and sit-to-stand training, it is essential to incorporate exercises that specifically target hip extension, such as squats and standing hip extension movements. These exercises should be performed with careful attention to safety and proper technique to ensure their effectiveness and minimize the risk of injury.

In this study, the muscle strength value was presented using the muscle strength/body weight ratio; this study was designed to exclude the influence of the body weight on muscle strength. A decreased muscular performance at the same body weight level reflects decreases in the actions of the nervous system on muscles and muscular contractility. These were regarded as aging-related changes in the elderly. As an item to be examined in the future, the number of subjects was smaller than a sample size calculated during the study period. However, the characteristics of aging-related changes in muscle strength could be clarified.

CONCLUSIONS

The primary goal of strength training interventions for older adults is to promote health and prevent the need for nursing care. Understanding the specific muscle groups that are most affected by aging during the intervention process may provide deeper insights into the factors contributing to ADL impairments and reduced mobility endurance, ultimately supporting improvements in these areas.

Notes

ACKNOWLEDGEMENTS

The authors thank the physical therapists team members for their extensive collaboration.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Conflicts of Interest

The authors declare no conflict of interest.

Fig. 1.

Methods for measuring muscle strength

Note: Resistance applied in the direction of the arrow

Fig. 2.

Muscle strength ratio between elderly and young subjects (O-A ratio)

Note: The O-Y ratio for hip extension (55.97±26.01%) was the lowest, followed by shoulder external rotation (69.89±30.63%), shoulder internal rotation.

Apf=Ankle plantar flexion; Adf=Ankle dorsiflexion; Kf= Knee flexion; Ke= Kee extension; Hf= Hip flexion; He= Hip extension; Hab= Hip abduction; Had= Hip adduction; Sf=Shoulder flexion; Sab=Shoulder abduction; Ser= Shoulder external rotation; Sir= Shoulder internal rotation; Ef= Elbow flexion

Table 1.

Comparison of background and muscle strength between the young and elderly subjects

	Young subjects (n=43)	Elderly subjects (n=38)	p-value	Effect size (d)
Age	20.33±0.47	78.34±7.67
Sex (M/F)	16/27	18/20
Height (cm)	164.07±8.51	154.85±8.83	0.001	1.06
Body weight (kg)	56.06±8.96	54.44±10.34	0.483	0.17
Body mass index (kg/m²)	20.72±2.06	22.61±3.23	0.002	0.71
Muscle strength (N/kg)
Ankle plantar flexion	3.23±0.43	2.97±0.80	0.319	0.41
Ankle dorsiflexion	2.32±0.42	2.02±0.41	0.001	0.72
Knee flexion	1.35±0.23	1.12±0.19	<0.001	1.08
Knee extension	1.93±0.39	1.63±0.25	<0.001	0.90
Hip flexion	2.35±0.41	1.80±0.59	<0.001	1.09
Hip extension	2.47±0.48	1.38±0.64	<0.001	1.94
Hip abduction	2.44±0.91	2.12±0.65	0.182	0.40
Hip adduction	2.25±0.77	1.92±0.56	0.080	0.49
Shoulder flexion	1.27±0.25	0.94±0.36	<0.001	1.08
Shoulder abduction	1.31±0.26	1.12±0.49	0.033	0.49
Shoulder external rotation	1.22±0.62	0.85±0.37	0.009	0.71
Shoulder internal rotation	1.24±0.57	0.88±0.35	0.002	0.75
Elbow flexion	1.43±0.32	1.22±0.34	0.004	0.64

All values were presented as mean ± SD

Concerning the effect size d=0.50 is regarded as significant.

|0.20| ≤ small < |0.50|

|0.50| < medium < |0.80|

|0.80| ≤ large

Table 2.

Muscle strength ratio between elderly and young subjects

	Percentage of the young subjects’ muscle strength (%)
Ankle plantar flexion	92.09±25.04
Ankle dorsiflexion	87.38±17.98
Knee flexion	82.98±14.23
Knee extension	84.82±12.95
Hip flexion	76.71±25.16
Hip extension	55.97±26.01
Hip abduction	86.71±26.49
Hip adduction	84.84±24.90
Shoulder flexion	74.63±28.60
Shoulder abduction	85.65±38.10
Shoulder external rotation	69.89±30.63
Shoulder internal rotation	70.62±28.52
Elbow flexion	85.70±23.61

All values were presented as mean ± SD

REFERENCES

1. Cabinet Office, Government of Japan. https://www8.cao.go.jp/kourei/whitepaper/w-2020/html/gaiyou/s1_1.html (access 3 August, 2024)

2. Pate RR, Pratt M, Blair SN, et al. Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA. 1995; 273(5):402–407.

3. An KO, Kim J. Association of sarcopenia and obesity with multimorbidity in Korean adults: a nationwide cross-sectional study. J Am Med Dir Assoc. 2016; 17(10):960.e961–967.

4. Falkel JE, Sawka MN, Levine L, et al. Upper to lower body muscular strength and endurance ratios for women and men. Ergonomics. 1985; 28(12):1661–1670.

5. Wilmore JH. Alterations in strength, body composition and anthropometric measurements consequent to a 10-week weight training program. Med Sci Sports,. 1974; 6(2):133–138.

6. Janssen I, Heymsfield SB, Wanq ZM, et al. Skeletal muscle mass and distribution in 468 men and woman aged 18-88 yr. J Appl Physiol. 2000; 89(1):81–88.

7. Teimoori A, Kordi MR, Choobine S, et al. The effects of aging on muscle strength and functional ability of healthyiranian males. World J Sport Sci. 2009; 2(4):261–265.

8. Al Snih S, Raji MA, Peek MK, et al. : Pain, lower-extremity muscle strength, and physical function among older Mexican Americans. Arch Phys Med Rehabil. 2005; 86(7):1394–1400.

9. Al-Abdulwahab SS. The effects of aging on muscle strength and functional ability of healthy Saudi Arabian males. Ann Saudi Med. 1999; 19(3):211–215.

10. Larsson L, Grimby G, Karlsson J, et al. Muscle strength and speed of movement in relation to age and muscle morphology. J Appl Physiol. 1979; 46(3):451–456.

11. Moreland JD, Richardson JA, Goldsmith CH, et al. Muscle weakness and falls in older adults: a systematic review and meta-analysis. J Am Geriatr Soc. 2004; 52(7):1121–1129.

12. Kerrigan DC, Lee LW, Collins JJ, et al. Reduced hip extension during walking: healthy elderly and fallers versus young adults. Arch Phys Med Rehabil. 2001; 82(1):26–30.