Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadriceps

Abstract

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-1. At the start and at every 20th day 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-1. After 60 days T leg CSA had increased by 8.5% +/- 1.4% (mean +/- SEM, n = 4, p less than 0.001), iEMG by 42.4% +/- 16.5% (p less than 0.01) and MVC by 20.8% +/- 5.4% (p less than 0.01). 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% (N.S.) and 8.7% +/- 4.3% (N.S.), respectively. The increase in quadriceps muscle CSA was maximal at 2/10 Lf (12.0% +/- 1.5%, p less than 0.01) and minimal, proximally to the knee, at 8/10 Lf (3.5% +/- 1.2%, N.S.). Preferential hypertrophy of the vastus medialis and intermedius muscles compared to those of the rectus femoris and lateralis muscles was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Combined Uphill-Downhill Sprint Training on Kinematics and Maximum Running Speed in Experienced Sprinters

“…The most reasonable explanation for the changes in the kinematic and force production characteristics, after 8 weeks of U+D training, was the occurrence of neural adaptations. Similar adaptations have been demonstrated in strength training [9,17,18] and explosive training studies [19][20][21] which include powerful anisometric single or multi joint contractions, as in the current study. These neural adaptations could be either improvement in neural drive to the muscle, by increasing the recruited number of motor units during contractions and/or by increasing the "firing" (excitation) rate of the motor units of the trained muscles, or/and changes in the muscular coordination, by redefying the recruiting strategy between motor units of the same muscle, or a group of synergist muscles [22,23].…”

Skeletal muscle substrate metabolism during exercise: methodological considerations

“…It is true that saphenous blood flow is relatively low, but some blood must be drained from the proximal thigh muscle, which has a slightly higher lactate concentration than blood from the more distal part to compensate for the low lactate level in the saphenous vein. This point of view is in accordance with the explanation given earlier for O 2 saturation, and agrees with the observation that after training the proximal part of the kneeextensor muscle enlarges more than the more distal portions both in young (Narici et al 1989(Narici et al , 1996 and older individuals (Kryger, 1998). Available data on glucose reveal similar concentrations when sampling in the proximal and distal direction of the femoral artery, with a tendency for glucose concentration to be slightly higher in the proximal direction ( Fig.…”

Assessing Voluntary Muscle Activation with the Twitch Interpolation Technique

“…Observations of increased surface EMG [79,80,81,82,83,84] , increased motor unit firing rates [85,86] , cross education [82,87,88,89,90,91] and enhanced reflex potentiation [92,93,94] are consistent with the possibility but none provides conclusive evidence.…”