Effects of triceps surae muscle strength and tendon stiffness on the reactive dynamic stability and adaptability of older female adults during perturbed walking

Abstract

This study aimed to examine whether the triceps surae (TS) muscle-tendon unit (MTU) mechanical properties affect gait stability and its reactive adaptation potential to repeated perturbation exposure in older adults. Thirty-four older adults each experienced eight separate unexpected perturbations during treadmill walking, while a motion capture system was used to determine the margin of stability (MoS) and base of support (BoS). Ankle plantar flexor muscle strength and Achilles tendon (AT) stiffness were analyzed using ultrasonography and dynamometry. A median split and separation boundaries classified the subjects into two groups with GroupStrong ( n = 10) showing higher ankle plantar flexor muscle strength (2.26 ± 0.17 vs. 1.47 ± 0.20 N·m/kg, means ± SD; P < 0.001) and AT stiffness (544 ± 75 vs. 429 ± 86 N/mm; P = 0.004) than GroupWeak ( n = 12). The first perturbation caused a negative ΔMoS (MoS in relation to unperturbed baseline walking) at touchdown of perturbed step (Pert), indicating an unstable position. GroupStrong required four recovery steps to return to ΔMoS zero level, whereas GroupWeak was unable to return to baseline within the analyzed steps. However, after repeated perturbations, both groups increased ΔMoS at touchdown of Pert with a similar magnitude. Significant correlations between ΔBoS and ΔMoS at touchdown of the first recovery step and TS MTU capacities (0.41 < r < 0.57; 0.006 < P < 0.048) were found. We conclude that older adults with TS muscle weakness have a diminished ability to control gait stability during unexpected perturbations, increasing their fall risk, but that degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations. NEW & NOTEWORTHY Triceps surae muscle weakness and a more compliant Achilles tendon partly limit older adults' ability to effectively enlarge the base of support and recover dynamic stability after an unexpected perturbation during walking, increasing their fall risk. However, the degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations.

Older adults demonstrate interlimb transfer of reactive gait adaptations to repeated unpredictable gait perturbations

“…These results indicate that the older adults responded to the treadmill belt acceleration perturbation with a more posterior X CoM and smaller BoS than young adults, delaying their stability 1 6 recovery. This differs to what we have previously observed using a cable-trip setup, where the differences have been observed in the BoS 8,34,35 , reflecting the differences in perturbation type. By the final perturbation of the trained leg, more posterior X CoM (not significant) and…”

“…smaller BoS values were still visible in the older adults compared to the young adults, but these no longer led to significantly different MoS AP values. Multiple studies have demonstrated the ability of healthy adults to reactively adapt gait in response to repeated perturbations [6][7][8][9] and the current study confirms these findings in a treadmill belt acceleration paradigm with stability-normalised walking speeds and walking speed normalised perturbations. Therefore, we can conclude that potential differences in the initial gait stability or perturbation characteristics likely do not play a large role in whether older adults adapt their response to repeated perturbations.…”

“…The ability to maintain or recover gait stability following unexpected mechanical perturbations such as trips, slips or ground surface changes is negatively affected in older age [1][2][3] which reflects older adults' increased falls risk during walking 4,5 . However, ageing does not greatly affect the ability to improve balance recovery responses to unexpected perturbations with repeated practice, nor the retention of these improvements over time [6][7][8][9] .…”

“…With this method, an equivalent baseline level of gait stability across participants is achieved and we can infer that any differences in the response to the perturbations are not, in whole or part, artefacts of the walking speeds of the participants, but rather due to true differences in recovery responses. Based on previous work in trips leading to forward balance loss 1,8 , we hypothesised that older adults would require more steps to recover stability than younger adults following the initial perturbation to each leg, despite the stability-normalised walking speed, but that both groups would be able to adapt their gait to improve stability over the repetitions to the left leg. The second aim was to determine if interlimb transfer of these adaptations could be observed in healthy older adults, despite the limited support in young adults in our previous study 24 .…”

Retention of gait stability improvements over 1.5 years in older adults: effects of perturbation exposure and triceps surae neuromuscular exercise

“…Given that the ability to create a large anterior step is important for maintaining dynamic stability during gait, it is not surprising that the age-related general degradation in the neuromuscular capacities of the lower limbs (Aagaard et al 2010;Csapo et al 2014;Karamanidis and Arampatzis 2006;Onambele et al 2006;Stenroth et al 2012) is often linked to reduced locomotor performance (Beijersbergen et al 2013;Kulmala et al 2014) and ineffective reactive recovery actions during perturbed gait (Epro et al 2018;Pijnappels et al 2005aPijnappels et al , 2005b. In particular, insufficient recovery responses after tripping have been related to age-induced deficits in the ankle plantarflexion moment in the push-off phase of human gait (Pijnappels et al 2004(Pijnappels et al , 2005a(Pijnappels et al , 2005b, indicating the importance of the triceps surae (TS) for recovery responses in perturbed gait.…”