Static contraction of the quadriceps muscle in man: Cardiovascular control and responses to one-legged strength training

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Abstract
Knee extension strength training of 1 leg (ST) (120 maximal contractions/day, 5 days/wk for 9 wks) was performed by 9 healthy young men. Before and after ST, biopsies were obtained from the vastus lateralis muscle of each leg and static quadriceps contractions (SQC) lasting 2 min were performed with each leg under control conditions and after combined vagal and .beta.-adrenergic blockade with atropine and metoprolol. Maximal voluntary contraction strength (MVC) increased more for the trained leg (TL) than for the untrained leg (UTL) but high circumferences and muscle fiber diameters gave little evidence for muscle hypertrophy. In pre- vs. post-training comparisons during SQC at the same relative force (40% of MVC) mean blood pressure (MBP), heart rate (HR) and smoothed rectified electromyographic activity were similar for TL and UTL. Similar findings were obtained for MBP after attenuation of the HR response by autonomic blockade, indicating that MBP, per se, was closely linked to the relative force of SQC. Pre- to post-training reductions in MBP and HR during SQC with each leg at an absolute force of 40% of pre-training MVC were likely due to changes in the pattern of motor unit activation. A lower MBP response to SQC and TL than of UTL after training correlated with a greater capillary density and a lower muscle lactate level for TL.