http://orcid.org/0000-0002-2410-247X
1. Introduction
Regarding physiological changes of aging process, several studies have highlighted progressive biomechanical adaptations of the lower limbs across different modes of locomotion and intensities (i.e. walking, running, stair-climbing and sit-to-stand) leading to an alteration of the functional capacities (Beijersbergen et al. Citation2013). Especially, a redistribution of joint torque and power changes the relative contribution of the individual muscles to the total torque and power outputs of the lower limbs.
The ability of the elderly to perform activities of daily living also depends on the preservation of the ability to perform multi-joint movements requiring high power exertion (Trombetti et al. Citation2016). Within this context, a vertical jump is a relevant test to gain mechanistic insight into maximal lower limb capability and shows strong correlations with other standard tests performed by the elderly. In addition, mechanical joint work appears to be an appropriate parameter to assess joint contribution during vertical jumping, since the sum of all joints work is directly related to the total vertical displacement of the body mass center and the vertical jump height. To the best of our knowledge, only Wang’s study (2008) has reported an analysis of mechanical joint work during vertical jumping in a population of older men. Nevertheless, neither Wang (2008) nor the rest of the literature has reported information about joint contribution to the total mechanical work during explosive movements such as vertical jumping.
The purpose of the present study was to assess whether the mechanical joint work distribution was altered in the elderly during vertical jumping. It was hypothesized that, (1) there was a greater contribution of the proximal than the distal joints on the total mechanical joint work in the elderly and (2) the joint work was mostly affected by joint moments.
2. Methods
Eighteen healthy young males (Y) (mean ± SD; 21.85 ± 2.8 years; 1.78 ± 0.05 m; 69.9 ± 10.2 kg) and 21 healthy elderly participants (E) (mean ± SD; 74.5 ± 4.6 years; 1.70 ± 0.05 m; 79.2 ± 10.2 kg) volunteered to participate in this study, which was approved by the ethical committee of the Institutional Review Board of the University of Lyon.
Inclusion criteria for elderly were being (a) be over 65 years old, (b) actively participate in structured group exercise, (c) engage in at least 150 minutes of moderate-intensity aerobic physical activity throughout the week. Exclusion criteria were (a) severe cardiopulmonary and (b) neurological impairments; (c) balance disorders, or (d) recent musculoskeletal troubles. The young participants had to (a) be between 18 and 30 years old, (b) practice two hours of physical activity per week (self-reported) and (c) not present recent or current musculoskeletal disorders.
All subjects subsequently performed three maximal two-legged squat jumps (SJ), with participants’ hands on their hips and without countermovement. A three-minute rest interval was set to avoid the effect of muscle fatigue. The initial squat depth was self-selected. Reflective markers were placed on the left side of the body (acromion, greater trochanter, lateral femoral epicondyle, lateral malleolus and fifth metatarsophalangeal joint). Participants performed the SJ on a single force platform (1000 Hz, AMTI, model OR6-7-2000) and were filmed in the sagittal plane with a 100-Hz camcorder (Ueye, IDS UI-2220SE-M-GL).
Vertical jump height was determined with force plate data and the trial with the highest was value was kept for analysis. Videos of the SJ were used to digitize marker positions. A 2D kinematic model composed of four rigid segments was implemented. Joint ranges of motion (RoMs) were equal to the difference between the joint angle at takeoff and the joint angle at the start of the push-off.
Net intersegmental forces and joint moments were calculated using a bottom-up inverse dynamic procedure. Net joint moments were normalized with respect to the participant’s body mass. Then, the mechanical work (W) for each joint was calculated by integrating the joint moment with respect to the joint angle during the push-off phase.
Vertical jump height was compared between the two groups (E vs Y) using an independent Student’s t-test. The interaction effect between the group and the joint on the mechanical joint work, mean joint moment and the RoM were tested using linear mixed models. The p-values were obtained by likelihood ratio tests. The level of significance was set at p < 0.016 (Bonferroni correction: 0.05/3 dependent variables). When a significant effect was revealed by the linear mixed-model, post-hoc comparisons were performed using the Tukey test’s (p-value < 0.05). Effect sizes (ES: Glass's Δ) were reported for significant results.
3. Results and discussion
According to previous studies about motor performance in explosive movements (Beijersbergen et al. Citation2013) the elderly group was characterized by a 64% lower vertical jump height in comparison to the young group (0.36 ± 0.11 m vs. 0.13 ± 0.05 m, p < .001).
Linear mixed models did not reveal any interaction effect between the group and the joint on the mechanical joint work (χ2(2) ϵ [5.73], p = .057) or the joint moment (χ2(2) ϵ [6.99], p = .030), or RoM (χ2(2) ϵ [7.50], p = .025). Our first hypothesis was, therefore, not supported since the joint contribution to the total mechanical work was similar between the elderly and young adults ().
Figure 1. Percentage of the total mechanical work explained by the ankle, knee and hip joints during the SJ push of phase.
Nevertheless, a main effect of the group was observed for mechanical joint work (F(1,115) = 32.01, p < .001) with a ankle, knee and hip joint works lower in the elderly compared to the young group (−42% on average; ). Several studies have observed a greater dependence on the more proximal joints (i.e. hip or knee joints or both) and less emphasis on the distal joints (i.e. ankle joints) during gait, running, sprinting (Kulmala et al. Citation2014) or stair ascent and descent in the elderly. Vertical jumping is characterized by a simultaneous two-leg force production and could be affected by a bilateral deficit in contrast to previous studies, which may have influenced the reorganization of lower limb joint work in a different way.
Table 1. Mean and standard deviation values of the characteristics of the two groups on squat jumping task (elderly and young adults).
Concerning the joint moment, the elderly group produced lower values (F(1,115) = 27.72, p < .001) compared to the younger group (−30% on average). Nevertheless, no difference was observed between the two populations concerning the RoM (F(1,115) = 0.42, p < .52; ). These results confirm that joint work difference between the two population was mostly affected by joint moments. Our findings are in accordance with the age-related decline in force generation capacity which occurs in lower limb muscle groups and lower force production related to the change of the muscle contractile properties with the aging process.
4. Conclusions
Despite the reduced mechanical work of the ankle, knee and hip joints, we found that the elderly did not compensate for distal joint impairments with the proximal joints in contrast to outcomes observed during walking or running activities. Through the comparative analysis of the mechanical joint work of young and elderly populations, we found that age-related changes were mainly explained by deficits in the joint moment during squat jumping. Consequently, improving the strength of all lower limb joints may be relevant for clinicians in order to improve the ability to perform daily life activities, especially those involving explosiveness, such as preventing the risk of falls, among the others (Skelton and Beyer Citation2003).
References
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