Fatigue effects on the knee extensor rate of torque development scaling factor during ballistic isometric contractions in physically active individuals

Purpose To investigate the effects of a fatiguing protocol on the knee extensors' rate of torque development scaling factor (RTD-SF) during ballistic isometric contractions in physically active individuals. Methods The authors used a cross-over study design. Ten physically active male participated in two testing conditions: fatigue and control. Maximal voluntary isometric contraction (MVIC) was evaluated, followed by baseline and post-fatigue RTD-SF assessments using an isokinetic dynamometer. RTD-SF was evaluated with 20 knee extensor ballistic isometric contractions at four intensities: 20, 40, 60, and 80% MVIC. Three RTD-SF calculation methods and their consistencies (R-2) were analyzed according to two different phases of the torque-time curve: from the onset to the 50 ms time point, and between the 50 ms time point and the peak torque value. The fatiguing protocol consisted of 30 maximal concentric repetitions of the knee flexors and extensors at an angular velocity of 180 degrees<middle dot>s(-)(1), with a range of motion of 90 degrees. Results The absence of interaction between conditions and moments indicated no fatigability effect on RTD-SF and on its consistency, regardless of the rate of torque development (RTD) phase. The fatigue condition showed RTD-SFpeak of 9.6 +/- 3.2 and R(2)peak of 0.681 +/- 0.200 at baseline, compared to RTD-SFpeak of 9.6 +/- 2.4 and R(2)peak of 0.761 +/- 0.107 post-fatigue; the control condition showed RTD-SFpeak of 10.5 +/- 3.2, and R(2)peak of 0.745 +/- 0.176 at baseline, compared to RTD-SFpeak of 11.3 +/- 2.6, and R(2)peak of 0.786 +/- 0.133 post-rest. The other RTD-SF values for different RTD intensities followed similar trends (p > 0.05). Conclusion Knee extensor RTD-SF, as well as its consistency (R-2), are not affected by muscle fatigability.