The Relationship of Forearm Flexion Isometric Strength, Endurance, and Fiber Composition; and the Effect of Heating*

Abstract

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.

Effect of temperature on handgrip holding time.

“…The pH balance of the cell is seightrand maximum crucial for the optimum functioning of the enzyme tronger relationships systems. Alterations in the cytoplasmic pH may change veigh and m axm the chemical bond relationships in the enzyme molecule, (Breompoit i 1982a thereby changing the quaternary structure of the protein (Barter et al, 1982; possibly, causing a loss of function (Karp, 1979). An important rate limiting enzyme in the energy release id a significant corre-pathway, phosphofructokinase, is known to be sensitive d sirengnifant correto the hydrogen ion concentration (Edington and sgstrength and body Edgerton, 1976).…”

“…For example, 80% MVC for forearm flexion has been reported as 32.2 ± 9.8 seconds (Barter et al, 1982),…”

“…In experimental situations it has been easy to raise or lower intramuscular temperature by immersion in water (Binkhorst et al, 1977: Clarke et al, 1958Edwards et al, 1972). Elevation of intramuscular temperature by a few degrees centigrade has been shown to reduce handgrip endurance (Clarke et al, 1958), forearm flexion isometric endurance (Barter et al, 1982) and knee extension isometric endurance (Edwards et al, 1972) significantly. While reducing intramuscular temperature tends to increase holding time duration (Clarke et al, 1958).…”

“…While reducing intramuscular temperature tends to increase holding time duration (Clarke et al, 1958). The percentage maximum voluntary contractions (MVC) used by these studies varied from 33% MVC (Clarke et al, 1958) to 80% MVC (Barter et al, 1982). Humpreys and Lind (1963) reported that percentage MVC's of 70% or greater were probably required to cause occlusion of blood flow through forearm muscles.…”

Influence of type of MVC test on electromyography measures of biceps brachii and triceps brachii

“…Barter et al [23] and Miller et al [24] obtained similar results in TB: 32.5 and 32.7%, respectively. However, according to Schantz et al [25], it was 50% in TB.…”