Author(s): BÉTUS, Y., CATTAGNI, T., PERRIN, A., COLARD, J., NOSAKA, K., BOUREAU, A.S., CHAPELET, G., CORNU, C., JUBEAU, M., Institution: NANTES UNIVERSITÉ, Country: FRANCE, Abstract-ID: 903

INTRODUCTION:
Resistance training is an effective strategy to counteract age-related neuromuscular deficits (1). In older adults, eccentric contractions are associated with lower perceived exertion and reduced metabolic demands, making them particularly suitable for resistance training interventions (2). However, eccentric exercise may also elicit greater neuromuscular fatigue and increase the risk of muscle damage (3). Muscle length has been identified as a key factor modulating these neuromuscular responses to eccentric exercise (4). However, the combined influence of eccentric contractions and muscle length on neuromuscular responses has not yet been investigated in older adults. Therefore, this study aimed to examine the acute and delayed neuromuscular responses to eccentric contractions performed at different muscle lengths in young and older adults.
METHODS:
Twenty-four young and twenty-six older adults participated in this study. Participants were assigned to either a short or long muscle length condition during maximal eccentric plantarflexor exercise, defined by the ankle joint angle (30° to 0° plantarflexion and 0° to −30° dorsiflexion, respectively). The exercise bout consisted of 10 sets of 10 maximal eccentric contractions. Maximal voluntary isometric contraction (MVIC) torque was assessed before, immediately after, and 1 h, 24 h, and 48 h post-exercise. Additional neuromuscular assessments, i.e., evoked responses and voluntary activation, were also performed.
RESULTS:
Despite a similar torque–time integral in both age groups, a muscle length condition effect was observed only in younger participants, with a greater immediate post-exercise reduction in MVIC torque at long compared with short muscle length condition (−28.1% vs. −8.9%, p = 0.031). In contrast, older adults showed similar MVIC torque losses across muscle length conditions (≈ −14–21%, p = 0.179). Evoked responses did not differ between age groups but were greater during the long muscle length condition, whereas voluntary activation differed significantly between age groups (p = 0.019). All variables returned to baseline within 24 h for all groups independently of muscle length condition, indicating no muscle damage
CONCLUSION:
Eccentric contractions performed at long muscle length induced greater immediate force loss in young adults, whereas muscle length did not modulate neuromuscular responses in older adults, despite a similar mechanical load during exercise. These findings indicate that, in older adults, eccentric exercise of the plantarflexors at long muscle length can be performed without exacerbating immediate and delayed neuromuscular impairments, supporting its safe use in resistance training interventions targeting this muscle group.
(1) Fragala et al., 2019 (2) Cvečka et al., 2023 (3) Hayes et al., 2023 (4) Guilhem et al., 2016