Alterations in Leg Extensor Muscle-Tendon Unit Biomechanical Properties With Ageing and Mechanical Loading

Abstract

Tendons transfer forces produced by muscle to the skeletal system and can therefore have a large influence on movement effectiveness and safety. Tendons are mechanosensitive, meaning that they adapt their material, morphological and hence their mechanical properties in response to mechanical loading. Therefore, unloading due to immobilization or inactivity could lead to changes in tendon mechanical properties. Additionally, ageing may influence tendon biomechanical properties directly, as a result of biological changes in the tendon, and indirectly, due to reduced muscle strength and physical activity. This review aimed to examine age-related differences in human leg extensor (triceps surae and quadriceps femoris) muscle-tendon unit biomechanical properties. Additionally, this review aimed to assess if, and to what extent mechanical loading interventions could counteract these changes in older adults. There appear to be consistent reductions in human triceps surae and quadriceps femoris muscle strength, accompanied by similar reductions in tendon stiffness and elastic modulus with ageing, whereas the effect on tendon cross sectional area is unclear. Therefore, the observed age-related changes in tendon stiffness are predominantly due to changes in tendon material rather than size with age. However, human tendons appear to retain their mechanosensitivity with age, as intervention studies report alterations in tendon biomechanical properties in older adults of similar magnitudes to younger adults over 12–14 weeks of training. Interventions should implement tendon strains corresponding to high mechanical loads (i.e., 80–90% MVC) with repetitive loading for up to 3–4 months to successfully counteract age-related changes in leg extensor muscle-tendon unit biomechanical properties.

A trip to remember

“…be found. The first and second hypotheses regarding adaptation and retention were confirmed, as significant improvements in MoS and number of steps to MoS Base during the perturbations to the left leg on the first day were observed, and these improvements were (almost completely) retained during the first perturbation to the left leg on the second measurement day (post one month), confirming previous work demonstrating adaptation and retention in reactive gait stability (Bhatt et al, 2012, Pai et al, 2014b, Epro et al, 2018a, Epro et al, 2018b. The third hypothesis regarding savings was confirmed in post-hoc analyses, as the pre-planned analysis could not confirm this due to the unexpected extent of the retention observed.…”

“…Our results demonstrated that young healthy adults are capable of almost fully retaining reactive adaptations in gait over a period of one month. Previous work has repeatedly demonstrated partial retention of reactive gait adaptations in healthy adults (Bhatt et al, 2012, Pai et al, 2014b, Liu et al, 2017, Epro et al, 2018b. The reasons why our participants demonstrate almost full retention are unclear, but could be related to the nature of the perturbation, the normalisation procedure or awareness of the task.…”

“…Despite evidence of feedback-driven adaptation in these reflexes during specific stimulation or joint level perturbations and in gait stability control following whole body mechanical perturbations, whether or not this translates to the retention, savings and interlimb transfer of adaptations in reactive gait stability following mechanical, whole body perturbations such as slips and trips has not, to our knowledge been addressed in the literature. There is evidence to suggest that humans can at least partly retain reactive adaptations in gait stability over different time periods of months to years (Bhatt et al, 2012, Pai et al, 2014b, Liu et al, 2017, Epro et al, 2018b. However, no study has examined savings and the interlimb transfer of reactive gait adaptations to standardised, controlled whole body (mechanical) perturbations.…”

“…Humans are capable of rapidly adapting gait kinematics in both reactive , McCrum et al, 2017b, Epro et al, 2018a and predictive Bastian, 2015, McCrum et al, 2016a) manners and such adaptation can be retained over time (Bhatt et al, 2012, Pai et al, 2014b, Roemmich and Bastian, 2015, Epro et al, 2018b and transferred between different locomotor tasks and environmental conditions (Bieryla et al, 2007, Reisman et al, 2009, Torres-Oviedo and Bastian, 2010, Parijat and Lockhart, 2012, Long et al, 2015. In particular, reactive gait adaptations are of great interest for falls prevention research and are the focus of perturbation-based balance training for populations at an increased risk of falls (Pai and Bhatt, 2007, Mansfield et al, 2010, Pai et al, 2014a, Mansfield et al, 2015b, McCrum et al, 2017b, Epro et al, 2018b. However, the retention (a preservation over time of adaptations made previously), savings (faster re-adaptation on re-exposure to a perturbation) and transfer (changes in an untrained limb or task reflecting, at least to some extent, the changes seen in the trained limb or task) of reactive gait adaptations are not yet well understood, despite their importance for falls prevention interventions.…”

Age-related Changes in Motor Function (I). Mechanical and Neuromuscular Factors

“…Some differences in the results may be the consequence of technical and methodological differences between studies [68,69], but the prevalent evidence appears to suggest a reduction in tendon stiffness and Young's modulus with advancing age. Furthermore, the similar relative declines with aging in Young's modulus suggest that ▶ the age-related decline in stiffness may be predominantly due to alterations in tendon material properties [70].…”