Characteristics of quadriceps fatigue induced by continuous maximal knee extension among young and elderly adult men with different levels of physical activity

Abstract

BACKGROUND:

Skeletal muscle strength can be impacted by various factors. However, the possible effects of different forms of exercises on the elderly’s muscle strength remain unknown. Furthermore, whether the level of physical activity influences the effects of an exercise-based training also remains unclear.

OBJECTIVE:

To investigate the characteristics of fatigued quadriceps by continuous maximum knee extension movements among different male groups under different physical conditions.

METHODS:

A total of 36 male participants (24 elderly and 12 youth) were divided into three groups, namely, young male group, and two groups of elderly participants: physically active and physically inactive. All groups underwent two sets of fatigue procedures. They initially finished 30 isokinetic maximum knee extension contractions at 60 ${}^{\circ }$ /s. Three days later, they completed 50 isokinetic maximum knee extension at 180 ${}^{\circ }$ /s. Then, their muscle strength characteristics were assessed.

RESULTS:

During the 60 ${}^{\circ }$ /s fatigue test the total work of the dominant and non-dominant quadriceps in the two elderly groups was significantly lower than that of the young male group ( $p<$ 0.05). Moreover, the total work of dominant quadriceps in physically active elderly male group was significantly higher than physically inactive male group in the middle (71.1 $\pm$ 12.0 vs. 52.0 $\pm$ 18.5 J) and the last third (60.9 $\pm$ 8.6 vs. 44.4 $\pm$ 15.4 J, $p<$ 0.05). During the 180 ${}^{\circ }$ /s fatigue test the total work of dominant and non-dominant quadriceps in young male group was significantly higher than their elderly counterparts ( $p<$ 0.05). Moreover, the total work of dominant quadriceps in physically active elderly male group was significantly higher than in the physically inactive male group in the first (48.9 $\pm$ 4.6 vs. 31.7 $\pm$ 6.3 J), the middle (41.2 $\pm$ 4.8 vs. 26.1 $\pm$ 3.5 J), and the last third (33.3 $\pm$ 7.0 vs. 20.3 $\pm$ 3.1 J, $p<$ 0.05).

CONCLUSION:

Exercise is associated with improved function and fatigue resistance of the quadriceps in elderly people. Moreover, the implications of the bilateral quadriceps’ imbalance in this group may be of functional importance and should thus be clinically considered.

1. Introduction

Falling accidents are a serious public health problem as people age. Falls can lead to severe physical, psychological and economic consequences among older adults. Therefore, developing effective fall prevention programs is a pressing need.

The effects of sports on the improvement of the human skeletal muscle’s function has become the focus of many sports experts who paid considerable attention to muscle function evaluation and strength improvement for the elderly [1, 2, 3] since muscle weakness is a key fall risk factor that possibly affects the quality of life among older adults. Muscle strength loss in the elderly can easily produce limb weakness and cause problems, such as difficulty in rising from bed or chair, slow gait, imbalance and falls [4]. In an examination on the effect of sports on improving strength among older adults, Rui et al. found that 16 weeks of regular shadowboxing exercise could significantly improve the muscle strength of lower limbs and proprioception function in the elderly [5]. It also improved neuromuscular control ability of lower limbs but only slightly influence the balance function. Thus, shadowboxing exercise should be applied as a possible preventive measure against falling [5].

Skeletal muscle strength can be impacted by various factors. However, the possible effects of different forms of exercises on the elderly’s muscle strength remain unknown. Whether the level of physical activity can influence the effects of an exercise-based training also remains unclear. Therefore, the purpose of this study was to investigate the characteristics of fatigued quadriceps by continuous maximum knee extension movements among different male groups under different physical conditions.

2. Methods

2.1 Participants

A total of 36 community dwelling male subjects (12 younger and 24 older adults) were screened by consultation and questionnaire survey and enrolled in this study (Table 1). All participants volunteered to participate. Subjects were divided into three groups in accordance with the experimental needs, namely, young male group (OYP), physically active elderly male group (REE) and physically inactive elderly male group (IEE). The REE and IEE groups were divided according to the level of the physical activity in the questionnaire, namely, 0–1 $=$ low-intensity (1 hour per week); 5 $=$ high-intensity (20 hours per week). Subjects were screened carefully before the experiment. They were then asked to participate in the experiment voluntarily and were provided physical examination reports. The medical examination included but was not limited to cardiac examination, sports injury examination and major surgery to ensure that the subjects’ physical conditions met the requirements of this experiment and the experiment cooperation agreement. This study was approved by the Institutional Review Board of the Shaoxing University. Informed written consent was obtained from each participant.

Table 1

Subjects’ information

Groups	Age (years)	Weight (kg)	Height (cm)
Physically inactive	67.28 $\pm$ 3.1	63.77 $\pm$ 12.2	164.45 $\pm$ 8.2
elderly ( $n=$ 12)
Physically active	66.83 $\pm$ 2.4	62.65 $\pm$ 9.4	166.93 $\pm$ 9.2
elderly ( $n=$ 12)
Young adults	24. 58 $\pm$ 2.1	61.34 $\pm$ 7.3	170.67 $\pm$ 10.1
( $n=$ 12)

2.2 Procedure

A CON-TREX isokinetic dynamometer (Physiomed GmbH, Germany) was used for muscle strength measurement. The pre-experiment was conducted 1 week before the experiment. In this stage, subjects were familiarized with the whole process and were handed notes for daily activities. Before the formal experiment, subjects warmed up on a cycle ergometer for 5 minutes. During the actual experiment, subjects were required to complete 30 continuous maximal knee concentric extensions (at a RoM of $\approx$ 85 ${}^{\circ }$ ) at 60 ${}^{\circ }$ /s. The dominant quadriceps were tested initially, followed by its non-dominant counterpart. The total work (TW) data of the consecutive contractions of 30 times was then was recorded. Three days later, subjects were tested at 180 ${}^{\circ }$ /s and the TW of 50 consecutive contractions was recorded. Then, the average work of the first 1/3, the middle 1/3 and the last 1/3 of the TW was analysed.

2.3 Statistical analysis

The experimental data collected were statistically processed using SPSS18.0 statistical software. The data in the Table was expressed in mean $\pm$ standard deviation. The measurements were analysed by two-way ANOVA. A $p<$ 0.05 was set as a threshold for significant differences.

3. Results

During the fatigue test with 30 repetitons at 60 ${}^{\circ }$ /s knee extensions in the dominant side (Fig. 1), the TW values of quadriceps in REE group for the first, middle and last thirds were : 77.8 $\pm$ 16.1, 71.1 $\pm$ 12.0 and 60.9 $\pm$ 8.6 J, respectively while for the IEE group they were 59.7 $\pm$ 23.0, 52.0 $\pm$ 18.5 and 44.4 $\pm$ 15.4 J, respectively. Both were significantly inferior to the OYP group: 136.4 $\pm$ 41.2, 121.5 $\pm$ 39.0, 105.4 $\pm$ 38.4 J, respectively at each third of the fatigue phase ( $p<$ 0.05). However, the TW values for REE were significantly higher than those for the IEE at the middle and last third ( $p<$ 0.05).

Figure 1.

The TW of dominant quadriceps with 30 times 60 ${}^{\circ }$ /s knee extensions among three groups in the first 1/3, the middle 1/3 and the last 1/3 fatigue phase. Note: OYP, young male groups; REE, physically active elderly male groups; IEE, physically inactive elderly male groups; ${}^{\mathrm{\#}}$ indicates significant differences between two groups ( $p<$ 0.05).

Figure 2.

The TW of non-dominant quadriceps with 30 times 60 ${}^{\circ }$ /s knee extensions among three groups in the first 1/3, the middle 1/3 and the last 1/3 fatigue phase. Note: OYP, young male groups; REE, physically active elderly male groups; IEE, physically inactive elderly male groups; ${}^{\mathrm{\#}}$ indicates significant differences between two groups ( $p<$ 0.05).

Figure 3.

The TW of dominant quadriceps with 50 times 180 ${}^{\circ }$ /s knee extensions among three groups in the first 1/3, the middle 1/3 and the last 1/3 fatigue phase. Note: OYP, young male groups; REE, physically active elderly male groups; IEE, physically inactive elderly male groups; ${}^{\mathrm{\#}}$ indicates significant differences between two groups ( $p<$ 0.05).

Figure 4.

The TW of non-dominant quadriceps with 50 times 180 ${}^{\circ }$ /s knee extensions among three groups in the first 1/3, the middle 1/3 and the last 1/3 fatigue phase. Note: OYP, young male groups; REE, physically active elderly male groups; IEE, physically inactive elderly male groups; ${}^{\mathrm{\#}}$ indicates significant differences between two groups ( $p<$ 0.05).

For the non-dominant side (Fig. 2) at same test conditions, the TW values of quadriceps in OYP group were respectively 120.8 $\pm$ 33.7, 108.9 $\pm$ 28.3 and 97.3 $\pm$ 26.1 J, and significantly higher than those of the REE group (75.4 $\pm$ 12.0, 69.4 $\pm$ 10.8, 61.5 $\pm$ 11.4 J) and IEE group (59.6 $\pm$ 24.2, 53.0 $\pm$ 18.0, 45.9 $\pm$ 13.1 J, $p<$ 0.05) at each third of the fatigue phase. However, there was no significant difference between REE and IEE group.

During the fatigue test with 50 repetitions at 180 ${}^{\circ }$ /s in the dominant side (Fig. 3), the TW values of quadriceps in OYP group were 90.8 $\pm$ 22.0, 67.6 $\pm$ 13.7, 43.9 $\pm$ 7.1 J and significantly higher than either those of REE: 48.9 $\pm$ 4.6, 41.2 $\pm$ 4.8 and 33.3 $\pm$ 7.0 J, or of the IEE: 31.7 $\pm$ 6.3, 26.1 $\pm$ 3.5 and 20.3 $\pm$ 3.1 J, respectively at each third of the fatigue phase ( $p<$ 0.05). Moreover, the TW values of quadriceps in REE group was significantly higher than IEE group at each third of the fatigue phase ( $p<$ 0.05).

For same test conditions in the non-dominant side the findings for OYP were (Fig. 4): 95.1 $\pm$ 14.9, 72.7 $\pm$ 11.0, and 49.4 $\pm$ 10.6 J and significantly higher than either in REE: 38.3 $\pm$ 7.4, 32.1 $\pm$ 4.9 and 25.1 $\pm$ 3.6 J or in IEE: 34.1 $\pm$ 15.4, 28.8 $\pm$ 12.8 and 23.7 $\pm$ 10.5 J, respectively, $p<$ 0.05. However, there was no significant difference between REE and IEE group.

4. Discussion

The purpose of this study was to determine the characteristics of quadriceps fatigue by continuous maximum knee extension movements among different groups under different physical conditions. The main findings of this study are: 1) the TW of the dominant and non-dominant quadriceps in the young male group is the highest among three groups at each third of the fatigue phase; 2) the TW of dominant quadriceps in the physically active elderly male group group is higher than in physically inactive elderly male group at each third of the fatigue phase except the first third during the fatigue test with 30 repetitons at 60 ${}^{\circ }$ /s knee extensions.

With increasing age, the decline of the heart and lung function can lead to a decrease in muscle strength, thereby possibly affecting the elderly’s daily activity. Li et al. reported that as the elderly’s body functions decline, the senile frailty syndrome appears while biological function and resistance to stress are significantly reduced thereby greatly increasing the elderly’s loss of life ability [6]. Although our results show that the TW of the quadriceps in the elderly was less than young people, the anti-fatigue ability of the quadriceps in REE group was better than that of IEE group which was affected by exercise. Exercise can have a positive impact on the muscular function of the elderly. The 30/50 times of continuous knee extensions also reflect the elderly peoples’ ability to perform sports continuously. The engagement of the elderly in continuous activities ensures the smooth completion of the corresponding movement if muscular function is strong enough thereby avoiding the phenomenon of falling due to the decline in muscle function. Qu et al. screened 70 elderly subjects with poor stability and divided them into the observation group and control group [7]. After 3 months of intervention, they analysed the indices of lower limb muscle strength, physical stability, and body flexibility. Shadowboxing and catwalk exercise were found to further improve the lower limb muscle strength, physical stability and body flexibility of the elderly. Therefore, frequent exercise, especially the scientifically-based which can improve quadriceps strength in the elderly, is important for this cohort.

The present results underline the ability of physically active elderly people to perform rapid knee extension on the dominant side, significantly better than the non-dominant’s one. However, there was no significant difference in the non-dominant side between REE and IEE groups. Similar to the results of this study, the studies by Wong et al. demonstrated that walking for more than 30 mins increased variability of the non-dominant limb at the knee joint in the physically active older adults [8].

The asymmetry in lower extremity strength has been reported as a risk factor for falls among older people [9]. LaRoche et al. observed that asymmetry in lower extremity strength led to a disruption in balance in older people aged 65 to 80 years [10]. Also, the older fallers demonstrated a significantly increased asymmetry in lower extremity strength than the older non-fallers [11]. Despite significant improvements in muscle strength in elderly male with physically active, the resulting imbalance in the extensor muscles of the lower extremities may still expose themselves to accidental falls. Therefore, for the elderly who frequently exercise, should pay attention to it in the exercise process, that is, to add the balance training of bilateral lower limb muscle strength. Moreover, the lowest performance was demonstrated by the physically inactive individuals. Although no balance test was conducted in this study, we speculated based on the results of previous studies that poor lower limb muscle strength could affect balance, thus increasing the risk of fall [12].

Several limitations should be considered in this study. On the one hand, we only focused on the TW of quadriceps, thus, the assessment of muscle force and activation level could be considered in the further research. On the other hand, there is currently no gold standard for age-specific fatigue protocols. In this study, the same fatigue protocol was applied to the elderly and the young, which could be optimized in the next phase of the study.

5. Conclusions

Exercise is associated with improved function and fatigue resistance of the quadriceps in elderly people. Moreover, the implications of the bilateral quadriceps’ imbalance in this group may be of functional importance and should thus be clinically considered.

Author contributions

CONCEPTION: Sihong Zhou and Weijie Fu.

PERFORMANCE OF WORK: Sihong Zhou and Feng Yang.

INTERPRETATION OR ANALYSIS OF DATA: Sihong Zhou, Zhi Zhou and Xini Zhang.

PREPARATION OF THE MANUSCRIPT: Sihong Zhou and Lixin Zheng.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Zhang Xini.

SUPERVISION: Lixin Zheng and Weijie Fu.

Ethical considerations

This study was approved by the Institutional Review Board of the Shaoxing University (approval number 2013-009). Written informed consent was obtained from each participant.

Funding

The research work was supported by the Natural Science Foundation of Zhejiang province of China (LY14C110001), the Talent Development Fund of Shanghai Municipal (2018107) and the “Dawn” Pro gram of Shanghai Education Commission (19SG47), China.