CHANGES IN MUSCLE MORPHOLOGY, ELECTROMYOGRAPHIC ACTIVITY, AND FORCE PRODUCTION CHARACTERISTICS DURING PROGRESSIVE STRENGTH TRAINING IN YOUNG AND OLDER MEN

Effects of a 10-week progressive strength training program composed of a mixture of exercises for increasing muscle mass, maximal peak force , and explosive strength (rapid force production) were examined in 8 y oung (YM) (29 +/- 5 yrs) and 10 old (OM) (61 +/- 4 yrs) men. Electromy ographic activity, maximal bilateral isometric peak force, and maximal rate of force development (RFD) of the knee extensors, muscle cross-s ectional area (CSA) of the quadriceps femoris (QF); muscle fiber propo rtion, and fiber areas of types I, IIa, IIb, and IIab of the vastus la teralis were evaluated Maximal and explosive strength values remained unaltered in both groups during a ii-week control period with no train ing preceding the strength training After the 10-week training period, maximal isometric peak force increased from 1311 +/- 123 N by 25.6% ( p < .05) in YM and from 976 +/- 168 N by 16.5% (p < .01) in OM. The pr etraining RFD values of 4049 +/- 791 Ns(-1) in YM and 2526 +/- 1197 N s(-1) in OM remained unaltered. Both groups showed significant increa ses (p < .05) in the averaged maximum IEMGs of the vastus muscles. The CSA of the QF increased from 90.3 +/- 7.9 cm(2) in YM by 12.2% (p < . 05) and from 74.7 +/- 7.8 cm(2) ill OM by 8.5% (p < .001). No changes occurred in the muscle fiber distribution of type I during the trainin g, whereas the proportion of subtype IIab increased from 2% to 6% (p < .05) in YM and that of type IIb decreased in both YM from 25% to 16% (p < .01) and in OM from 15% to 6% (p < .05). The mean fiber area of t ype I increased after the 10-week training in YM (p < .001) and OM (p < .05) as well as that of type IIa in both YM(p < .01) and OM (p < .01 ). The individual percentage values for type I fibers were inversely c orrelated with the individual changes recorded during the training in the muscle CSA of the QF (r = -.56, p < .05). The present results sugg est that both neural adaptations and the capacity of the skeletal musc le to undergo training-induced hypertrophy even in older people explai n the gains observed in maximal force in older men, while rapid force production capacity recorded during the isometric knee extension actio n remained unaltered during the present mixed strength training progra m.