Author(s): ANSALDO, M., SAZZI, C., BROCCA, L., PORCELLI, S., QUINLAN, J.I., PHLLIPS, B.E., SMITH, K., ATHERTON, P.J., NARICI, M., BOTTINELLI, R., PELLEGRINO, M.A., FRANCHI, M.V., Institution: UNIVERSITY OF PAVIA, Country: ITALY, Abstract-ID: 2172

INTRODUCTION:
Skeletal muscle aging is not only characterized by loss of muscle mass and power but also by mitochondrial impairments and reduced oxidative function (1). Resistance training (RT) is considered among the most effective strategies to counteract muscle atrophy and preserve muscle function (2). Moderate-intensity exercise based on eccentric (ECC) contractions has been proposed as an alternative to the classic conventional RT due to its potential efficacy in increasing muscle mass and function without requiring excessive effort for the elderly population (3,4). Notably, recent evidence showed significant improvement in mitochondrial function following chronic RT (5). However, the impact of eccentric-resistance training (ECC-RT) on mitochondrial adaptations is still not known. Thus, we investigated mitochondrial adaptations in response to 8 weeks of moderate ECC-RT in old (O) vs young (Y) individuals.
METHODS:
Eight O (67±1.3 y.o.) and eight Y (25±6 y.o.) subjects underwent 8 weeks of moderate-load ECC-RT consisting of 4 sets of 15 repetitions performed at 60% of ECC 1RM, 3 times/week. Before the first (PRE) and after the last (POST) training session, knee-extensors maximal voluntary isometric contraction (MVIC) torque was assessed at 3 different joint angles 60°, 70°, 80° and maximum isometric torque value obtained over the three joint angles was chosen as MVIC peak value. Muscle volume (QV) was measured by MRI. Muscle biopsies were also collected from the Vastus Lateralis and markers of mitochondrial biogenesis, content, and dynamics were analyzed by western blot. Data were analyzed by two-way ANOVA.
RESULTS:
After 8 weeks of eccentric resistance training, MVIC force increased in both O and Y (17 vs. 13%, respectively p<0.05 for both groups). QV increased in both O and Y (4% vs. 5%) (p<0.001) (p<0.01). After training, PGC-1α decreased in O (-44%, p<0.05) while no changes were observed in Y (p>0.05). TOM20 and CS decreased in O (-29% and -31% respectively, p<0.01) but they remained unaffected in Y (p>0.05). MNF1 increased in Y (+65%, p<0.05), while did not change in O (p>0.05). Regarding mitochondrial fission, levels p637DRP1 decreased in O (-41%, p<0.05) and not in Y (P>0.05); p616DRP1 increased in Y (+300%, p<0.05) and not in O (P>0.05).
CONCLUSION:
Despite the positive effect on muscle mass and strength in both O and Y, ECC-RT dampened mitochondrial biogenesis, reduced mitochondrial content, and promoted fission in O while both fission and fusion increased in Y. We can hypothesize an age-dependent response to moderate ECC-RT, with a negative effect on mitochondrial adaptations in O compared to Y. This is of particular interest, as such exercise modality, which could be tailored for elderly populations for its positive neuromuscular adaptations could not be entirely suitable for counteracting reductions in oxidative function.

(1) Tieland & Trouwborst & Clark 2017
(2) Hoppeler, 2016
(3) Quinlan et al, 2021
(4) Franchi & Reeves & Narici, 2017
(5) Mesquita et al, 2020