Influence of muscle length and force on endurance and pressor responses to isometric exercise

Abstract

Experiments were performed to determine whether endurance time, mean arterial pressure, or heart rate was related to either muscle length or external torque production in humans during isometric knee extension. Eight men and nine women performed isometric knee extension to the endurance limit at each of three muscle lengths, determined by knee angles of 40 degrees (0.698 rad, shortest), 60 degrees (1.047 rad, intermediate), and 90 degrees (1.571 rad, longest), and at intensities of 30 and 50% maximal voluntary contraction (MVC). Knee extension forms an ascending-descending length-torque curve, and lengths were chosen to result in different external torques. MVC was greatest at a knee angle of 60 degrees (P < 0.05 vs. 40 degrees, 90 degrees), with no significant difference between 90 degrees and 40 degrees. Endurance time was inversely related to muscle length, independent of torque production, at 30% MVC [40 degrees, 395 +/- 139 (SE); 60 degrees, 237 +/- 60; 90 degrees, 165 +/- 51 s; P < 0.05 vs. each other] and 50% MVC (40 degrees, 176 +/- 64; 60 degrees, 137 +/- 40; 90 degrees, 85 +/- 23 s; P < 0.05 vs. each other). Evidence is presented that endurance is a function of internal muscle force and not resultant external torque. The experimental design allowed the relationship of external torque and cardiovascular responses to be examined independent of exercise intensity. Muscle mass was also controlled in that the same muscle group was involved in all contractions. There were no differences in mean arterial pressure, heart rate, or rating of perceived exertion at any percentage of endurance time under any condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Caffeine on Fatigue During Submaximal Isometric Contractions at Different Knee Angles

“…This knee angle dependent endurance has previously been reported; Kooistra et al [3] showed, when using a similar intermittent protocol, quadriceps times to fatigue of 87.8 and 54.9 s for 30° and 90°, respectively. The current time to fatigue differences between angles also correspond well with other studies utilising single sustained contractions to exhaustion [1,2]. The slightly longer endurance times in the present study compared to Kooistra et al [3] may be explained by methodological differences.…”

“…Unilateral studies of skeletal muscles have shown that fatigue during sustained or intermittent isometric contractions is muscle length dependent [1,2]. For example, the endurance time of submaximal (i.e.…”

Knee extensor muscle oxygen consumption in relation to muscle activation

“…Thus, it is very relevant to investigate both muscle activation and muscle oxygen consumption during in vivo muscle activity at diVerent muscle lengths. Knee extensor endurance is greater at extended (short muscle length) compared to Xexed (long muscle length) knee angles during sustained isometric contractions to exhaustion, even at the same relative contraction intensity (Hisaeda et al 2001;Kooistra et al 2005;Ng et al 1994;Place et al 2005). One reason for this diVerence could be a diVerence in maximal voluntary activation between knee angles (de Ruiter et al 2004;Suter and Herzog 1997).…”

“…It would therefore be very interesting to examine muscle activation and oxygen consumption over a range of relative contraction intensities at extended compared to Xexed knee angles. In addition, insight into potential mechanisms limiting endurance at diVerent muscle lengths found previously (Hisaeda et al 2001;Kooistra et al 2005;Ng et al 1994;Place et al 2005) may be gained by the simultaneous investigation of muscle activation and oxygen consumption.…”

Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

“…TIME TO TASK FAILURE of a sustained submaximal isometric contraction (i.e., endurance time, ET) depends on physiological factors such as relative force level (30,35), muscle fiber type composition (16,51,77), muscular activation strategy (6,19,38), muscle size (36), and length (54,58) but also depends on psychological factors such as motivation, mood, and expectation (24). Whereas the task dependency of ET is well documented (23,25,26), little is known about muscle fatigue characteristics induced by a given task sustained until failure in different muscle groups, in the same individuals.…”