Changes in quadriceps twitch tension in response to resistance training in healthy sedentary subjects

Magnetic stimulation of the femoral nerve has been shown to evoke maximal quadriceps twitch contraction (TwQ(max)). Its measurement as a nonvolitional index of muscle strength has been proposed as a means to follow the disability of patients with neuromuscular disorders or peripheral muscle weakness. The aim of the present study was to investigate TwQ(max) sensitivity to interventions known to develop peripheral muscle strength. We thus measured changes in TwQ(max) after a short-duration resistance training program, examining its reproducibility and comparing its changes with other indices of muscle strength, such as maximal voluntary contraction (MVC) and one-repetition maximum (1-RM). In 23 subjects, TwQ(max)was measured on two occasions. High within- and between-session intraclass coefficients of correlation were observed (r > 0.99). Within-session and between-session differences in TwQ(max)were low (2.2 +/- 1% and 5.4 +/- 2%, respectively). Eight subjects subsequently participated in a resistance training program of the knee extensors, 3 days per week for 8 weeks. TwQ(max) and 1-RM increased significantly after training (10.9 +/- 3.7 vs. 12.3 +/- 4.4 kg, P < 0.04; and 45 +/- 13 vs. 55 +/- 12 kg, P < 0.001, respectively), whereas the MVC increase did not reach significance (41.9 +/- 16 kg vs. 42.3 +/- 15 kg, P = 0.25). Responses to magnetic stimulation of the femoral nerve are highly reproducible and sensitive enough to detect improvement in muscle contractile mechanisms after resistance training in healthy subjects. Patient cooperation is not required, which may be an advantage in clinical situations.