Neuromuscular adaptation during prolonged strength training, detraining and re-strength training in middle-aged and elderly people

Effects of a 24-week strength training performed twice weekly (24 ST) (comb ined with explosive exercises) followed by either a 3-week detraining (3 DT ) and a 21-week re-strength-training (21 RST) (experiment A) or by a 24-wee k detraining (24 DT) (experiment B) on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadric eps femoris, maximal isometric and one repetition maximum (1-RM) strength a nd jumping (J) and walking (W) performances were examined. A group of middl e-aged (M, 37-44 years, n = 12) and elderly (E, 62-77, n = 10) and another group of M (35-45, n = 7) and E (63-78, n = 7) served as subjects. In exper iment A, the 1-RM increased substantially during 24 ST in M (27%, P < 0.001 ) and E (29%, P < 0.001) and in experiment B in M (29%, P < 0.001) and E (2 3%, P < 0.01). During 21 RST the 1-RM was increased by 5% at week 48 (P < 0 .01) in M and 3% at week 41 in E (n.s., but P < 0.05 at week 34). In experi ment A the integrated electromyogram (IEMG) of the vastus muscles in the 1- RM increased during 24 ST in both M (P < 0.05) and E (P < 0.001) and during 21 RST in M for the right (P < 0.05) and in E for both legs (P < 0.05). Th e biceps femoris co-activation during the 1-RM leg extension decreased duri ng the first 8-week training in M (from 29 +/- 5% to 25 +/- 3%, n.s.) and e specially in E (from 41 +/- 11% to 32 +/-. 9%, P < 0.05). The CSA increased by 7% in M (P < 0.05) and by 7% in E (P < 0.001), and by 7% (n.s.) in M an d by 3% in E (n.s.) during 24 ST periods. Increases of 18% (P < 0.001) and 12% (P < 0.05) in M and 22% (P < 0.001) and 26% (P < 0.05) in E occurred in J. W speed increased(P < 0.05) in both age groups. The only decrease durin g 3 DT was in maximal isometric force in M by 6% (P < 0.05) and by 4% (n.s. ) in E. During 24 DT the CSA decreased in both age groups (P < 0.01), the 1 -RM decreased by 6% (P < 0.05) in M and by 4% (P < 0.05) in E and isometric force by 12% (P < 0.001) in M and by 9% (P < 0.05) in E, respectively, whi le J and W remained unaltered. The strength gains were accompanied by incre ased maximal voluntary neural activation of the agonists in both age groups with reduced antagonist co-activation in the elderly during the initial tr aining phases. Neural adaptation seemed to play a greater role than muscle hypertrophy. Short-term detraining led to only minor changes, while prolong ed detraining resulted in muscle atrophy and decreased voluntary strength, but explosive jumping and walking actions in both age groups appeared to re main elevated for quite a long time by compensatory types of physical activ ities when performed on a regular basis.