Knee extension isometric strength, rate of absolute and relative tension development, and vastus lateralis muscle fiber type composition was examined in 15 old (means = 64.5 years) and 9 young (means = 23.2 years) subjects. Strength was assessed using a 5-sec maximal voluntary contraction (MVC) and a fast maximal voluntary contraction (FMVC). MVC and FMVC were not significantly different in the Young group while in the Old group the FMVC was 19% greater than the MVC. These data suggested that usual strength testing methodology may considerably overestimate age-related strength loss. MVC, FMVC, and FT/ST muscle fiber area ratio were significantly lower in the Old group; rate of relative tension development was similar in Young and Old groups. FT/ST area ratio correlated with strength in the Young group and with rate of relative tension development in both groups. It was concluded that relative rate of tension development is unimpaired and related to FT fiber size while absolute tension level is impaired and unrelated to FT fiber size in the Old group.

Muscle fiber type and isokinetic strength and fatigue were examined in nine highly trained canoe and kayak paddlers. Needle biopsies were taken from the right vastus lateralis and biceps brachii muscles and the samples stained for myofibrillar ATPase. Baseline elbow flexion and knee extension isometric (0 degrees . s-1) and isokinetic (60 degrees . s-1 or 1.05 rad . s-1 and 180 degrees . s-1 or 3.14 rad . s-1) peak torques were determined. Each subject then performed two series of 50 isokinetic contractions at an angular velocity of 180 degrees . s-1: elbow flexion and knee extension series, separated by 3 h. The percentage of slow twitch fibers was similar in the biceps brachii (43.9%) and the vastus lateralis (43.3%). The fast twitch/slow twitch fiber area ratio was significantly higher in the more highly trained biceps brachii due to larger FT fibers. No relationship was found between fiber type composition and baseline peak torques or decline in peak torque due to the fatigue regimens. Baseline peak torque correlated with initial strength level, body weight, and limb girth. The results suggested that for these paddlers muscle strength and the decline in strength induced by repetitive isokinetic contractions were more dependent on characteristics of body size than on fiber type composition.

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Forearm flexion isometric strength and endurance and fiber composition of the biceps brachii were examined in ten college-age men. The isometric endurance exercise regimens were assessed at room temperature and in a heated water bath at 45 degrees C. On each session four baseline isometric strength trials (MVCs) were measured followed by three isometric endurance bouts with 11 min rest between bouts. Post-heating MVCs were assessed prior to the endurance bouts. Two types of isometric endurance times were measured: holding a weight amounting to (1) 50% of maximal strength (MVC) and (2) 80% MVC. The heat treatment significantly reduced both the baseline MVCs and the 50% and 80% MVC endurance times. Pre- and post-heating MVC measures did not correlate significantly with fiber type but did correlate with body weight and biceps girth. In the nonheated condition, endurance times were unrelated to fiber type or body size. However, in the heated condition, both 50% and 80% endurance times correlated negatively with percent fast-twitch fiber area, implying a selective influence of heat on muscle fiber types.