Muscle architectural adaptations are not associated with early-phase isokinetic strength increases

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Blazevich, AJ & Zhou, S 2002, 'Muscle architectural adaptations are not associated with early-phase isokinetic strength increases', paper presented to 3rd International Conference on Strength Training and Rehabilitation, Semmelweis University, Budapest, Hungary, 13-17 November.


INTRODUCTION: It was recently shown that rapid (within 5 weeks) muscle architectural adaptations can occur in athletes performing resistance training (RT). The purpose of the present study was to examine the magnitude of strength and architecture changes in previously untrained subjects performing maximal concentric/eccentric isokinetic training to determine whether they are related to the early strength changes observed with RT.

METHODS: Seven untrained men and 8 women completed 5 wk of unilateral (right leg), concentric/eccentric, isokinetic knee extension RT at 1.05 rad.s-1 (60o.s-1) while 7 men and 7 women served as non-training controls. Training was performed three times a week with four (weeks 1–2.5) or five (weeks 2.5–5) sets of 6 repetitions being performed with 1 min rest. Concentric and eccentric knee extensor torque of the right leg at 1.05 and 3.14 rad.s-1 (180o.s-1) was tested before and after 2.5 and 5 weeks of training. Fascicle angle (FA), fascicle length (FL), aponeurosis angle (AA), cross-sectional muscle thickness (MT) and physiological muscle thickness (PT; MT calculated perpendicular to line of muscle fascicles) at three regions of the vastus lateralis muscle was also measured using ultrasonography; the variables were calculated using Peak Motus software after the necessary muscle landmarks were digitised from ultrasound images.

RESULTS: Isokinetic torque changes for all subjects are shown in Figure 1. Concentric knee extensor torque at 1.05 rad.s-1 increased significantly after 5 wk in men and there was a near-significant increase in women after 2.5 wk (p<0.06, ES > 1.0). There were also significant increases in eccentric torque after 2.5 and 5 wk in both men and women. There were no significant changes in knee extensor torque at 3.14 rad.s-1 in any group and no strength changes in the control subjects. Despite significant strength increases after training, there were no changes in MT, PT, FL or FA in either control or training groups, although there were differences in MT and FA along the length of the vastus lateralis (PT and FL were only calculated at mid-length). Although concentric and eccentric torque were not correlated with MT and PT before the training, they were correlated significantly (r = 0.48 – 0.61; p<0.05) after the training.

DISCUSSION: The results suggest that changes in knee extension torque are rapid (2.5 wk) in previously non-strength trained subjects. The relatively greater increases in eccentric strength compared to concentric strength suggest a greater window of adaptation exists in the eccentric phase. These changes were not mirrored by adaptations in muscle architecture. Nonetheless, muscle size was related to strength after, but not before, training which implicates neural mechanisms as a factor affecting strength changes. Thus, while rapid architectural adaptations may occur in well-trained athletes, such adaptations appear not to occur in previously untrained subjects.