Human quadriceps cross-sectional area, torque and neural activation during 6 months strength training

Quadriceps muscle and fibre cross-sectional areas (CSA), torque and neural activation were studied in seven healthy males during 6 months of weight training on alternate days with six series of eight unilateral leg extensions at 80% of one repetition maximum. After training. the quadriceps cross-sectional area increased by 18.8±7.2% (P < 0.001) and 19.3±6.7 % (P < 0.001) in the distal and proximal regions respectively, and by 13.0±7.2% (P < 0.001) in the central region of the muscle. Hypertrophy was significantly different between and within the four constituents of the quadriceps. Biopsies of the vastus lateralis at mid-thigh did not show any increase in mean fibre cross-sectional area. Maximum isometric voluntary torque increased by 29.6±7.9-21.1±8.6% (P < 0.01 - 0.05) between 100° and 160° of knee extension, but no change in the optimum angle (110° - 120°) for torque generation was found. A 12.0±10.8 % (P < 0.02) increase in torque per unit area together with a right shift in the IEMG-torque relation and no change in maximum IEMG were observed. Time to peak isometric torque decreased by 45.8% (P < 0.03) but no change in time to maximum IEMG was observed. In conclusion. strength training of the quadriceps results in a variable hypertrophy of its components without affecting its angle-torque relation. The increase in torque per unit area. in the absence of changes in IEMG, may indicate changes in muscle architecture. An increase in muscle-tendon stiffness may account for the decrease in time to peak torque.