Neuromuscular performance of maximal voluntary explosive concentric contractions is influenced by angular acceleration

Abstract

Torque production during maximal voluntary explosive contractions is considered to be a functionally more relevant neuromuscular measure than steady-state torque, but little is known about accelerated concentric contractions. This study investigated torque, muscle activity, and fascicle behavior during isometric and fast concentric contractions of quadriceps femoris. Ten participants performed maximal voluntary explosive isometric, isovelocity, and additional concentric knee extensions at angular accelerations ranging from 700 to 4000° s that resulted in an angular velocity of 300° s at 40° knee flexion. Concentric torque at 40° knee flexion was corrected for inertia, and the corresponding isometric torque was matched to the time when the target knee angle of 40° was reached during concentric contractions. Electromyography of quadriceps femoris and hamstrings and ultrasound of vastus lateralis were measured to determine muscle activity, fascicle length, and fascicle velocity (FV). The faster the acceleration, the more torque was produced during concentric contractions at 40° knee flexion, which was accompanied by a reduction in FV. In comparison with isometric conditions, concentric quadriceps muscle activity was increased and torque during accelerations ≥3000° s equaled the time-matched isometric torque. Our results provide novel evidence that acceleration influences torque production during maximal voluntary explosive concentric contractions. This is suggested to be due to series elasticity and reduced force depression.

Shortening-induced residual force depression in humans

“…Assuming that rFD is caused by active muscle shortening and therefore already reduces the muscle's force-generating capacity during and not just after shortening, the typical rFD experiments (i.e., shortening-hold contractions) might not assess its relevance during many everyday contractions. Nevertheless, there are only few studies that addressed such so called dynamic force depression in muscles in vitro (4,29,37), and there are only some indirect observations from voluntarily activated muscles in vivo (18,19,31). By varying shortening amplitudes and speeds in isokinetic experiments and loads in isotonic experiments, McDaniel et al (37) has demonstrated that dynamic force depression dramatically alters isokinetic force output and isotonic shortening velocity of cat soleus muscle by 30 and 63%, respectively.…”

Muscle Belly Gearing Positively Affects the Force–Velocity and Power–Velocity Relationships During Explosive Dynamic Contractions

“…However, fascicle behaviour was not investigated, and the authors suggested that further research would be needed to assess whether structural and mechanical factors could also contribute to the observed differences in explosive torque production (Tillin et al, 2018). Hahn et al (2017) investigated torque production in order to provide insight into the influence of angular acceleration on maximal torque at matched angular position and velocity. They showed that the absolute torque generated during dynamic explosive contractions (from 10 to 4000 • /s 2 ) was lower than that obtained during fixed-end contractions but, in accordance with Tillin et al (2018), that the normalised torque generated during dynamic explosive contractions was larger than in fixed-end conditions (and increased with increasing angular acceleration).…”

Low-cost electromyography: validity against a commercial system depends on exercise type and intensity

“…The knee joint rotation was aligned with the dynamometer axis of rotation during a maximal voluntary contraction (MVC) at 60° of knee flexion. [10][11][12][13] Each participant performed a series of MVC with the right leg at 105, 90, 75, 60, 45 and 30° (0° = knee fully extended); two minutes of recovery time was interposed between contractions. The participants were instructed to contract as hard as possible from rest to maximum, but with a gradual increase (according to Maffiuletti et al 1 ; the duration of these contractions was 5 s. At each angle the contractions were repeated twice, and their average value was used for further analysis.…”

“…The signal gain and the sample rate of the two systems were: 60 dB and 16 bits for ZW and 40 dB (at 1000 Hz) and 10 bits for LC; the operating voltage was: 4 V for ZW and 3.3 V for LC. The sampling rate affects the resolution of the device: the commercial system can resolve 65536 (2 16 ) levels, whereas the LC systems has only 1024 of ideal range (2 10 ). Thus, the commercial system can detect more accurately small differences in time (AT).…”