Forty-two healthy men and women in two age groups (40 and 70 years) were examined for muscle cross-sectional area (CSA), maximal voluntary bilateral isometric force, force-time characteristics, maximal concentric 1 RM. and power performance of the leg extensors in a sitting position, squat jump, and standing long-jump. The results suggested that the decline in maximal strength with increasing age is related to the decline in muscle CSA; however, particularly in older women, the force/CSA ratio may also be lowered. Explosive force seems to decrease with increasing age even more than maximal strength. suggesting that muscle atrophy with aging is greater in fast-twitch fibers. The voluntary activation of the agonist and antagonist muscles seems to vary depending on the type of muscle action and/or velocity and time duration of the action in both age groups but to a greater extent in older people. There appears to be an age-related increase in antagonist co activation. especially in dynamic explosive movements.
K. Häkkinen: Department of Biology of Physical Activity. University of Jyväskylä. P.O. Box 35, 40351 Jyväskylä, Finland. M. Alen and M. Kallinen: Peurunka-Medical Rehabilitation and Physical Exercise Centre. Laukaa, Finland. M. Izquierdo: Laboratory of Biomechanics, Institute of Physical Education of León. León, Spain. K. Jokelainen, H. Lassila, and E. Mälkiä: Department of Health Sciences. University of Jyväskylä, Jyväskylä. Finland. W.J. Kraemer: Laboratory for Sports Medicine. The Pennsylvania State University, University Park, PA. R.U. Newton: School of Exercise Science and Sport Management, Southern Cross University, Lismore, Australia.