Abstract des Autors

Four male subjects aged 23-34 years were studied during 60 days of unilateral strength training and 40 days of detraining. Training was carried out four times a week and consisted of six series of ten maximal isokinetic knee extensions at an angular velocity of 2.09 rad/s. At the start and at every 20th days of training and detraining, isometric maximal voluntary contraction (MVC), integrated electromyographic activity (iEMG) and quadriceps muscle cross-sectional area (CSA) assessed at seven fractions of femur length (Lf), by nuclear magnetic resonance imaging, were measured on both trained (T) and untrained (UT) legs. Isokinetic torques at 30 degrees before full knee extension were measured before and at the end of training at: 0, 1.05, 2.09, 3.14, 4.19, 5.24 rad/s. After 60 days T leg CSA had increased by 8.5 +/- 1.4, iEMG by 42.4 +/- 16.5 and MVC by 20.8 +/- 5.4. Changes during detraining had a similar time course to those of training. No changes in UT leg CSA were observed while iEMG and MVC increased by 24.8 +/- 10 and 8.7 +/- 4.3, respectively. The increase in quadriceps muscle CSA was maximal at 2/10 Lf (12.0 +/- 1.5, and minimal, proximally to the knee, at 8/10 Lf (3.5 +/- 1.2). Preferential hypertrophy of the vastus medialis and intermedius muscles compared to those of the rectus femoris and lateralis muscles was observed. Isoangular torque of T leg increased by 20.9 +/- 5.4, 23.8 +/- 7.8 and 22.5 +/- 6.7 at 0, 1.05 and 2.09 rad/s respectively; no significant change was observed at higher velocities and in the UT leg. Hypertrophy produced by strength training accounts for 40 of the increase in force while the remaining 60 seems to be attributable to an increased neural drive and possibly to changes in muscle architecture.