The Effect of Leg Muscle Activation State and Localized Muscle Fatigue on Tibial Response during Impact

Abstract

The purpose of this research was to examine the effects of voluntarily manipulating muscle activation and localized muscle fatigue on tibial response parameters, including peak tibial acceleration, time to peak tibial acceleration, and the acceleration slope, measured at the knee during unshod heel impacts. A human pendulum delivered consistent impacts to 15 female and 15 male subjects. The tibialis anterior and lateral gastrocnemius were examined using electromyography, thus allowing voluntary contraction to various activation states (baseline, 15%, 30%, 45%, and 60% of the maximum activation state) and assessing localized muscle fatigue. A skin-mounted uniaxial accelerometer, preloaded medial to the tibial tuberosity, allowed tibial response parameter determination. There were significant decreases in peak acceleration during tibialis anterior fatigue, compared to baseline and all other activation states. In females, increased time to peak acceleration and decreased acceleration slope occurred during fatigue compared to 30% and 45%, and compared to 15% through 60% of the maximum activation state, respectively. Slight peak acceleration and acceleration slope increases, and decreased time to peak acceleration as activation state increased during tibialis anterior testing, were noted. When examining the lateral gastrocnemius, the time to peak acceleration was significantly higher across gender in the middle activation states than at the baseline and fatigue states. The acceleration slope decreased at all activation states above baseline in females, and decreased at 60% of the maximum activation state in males compared to the baseline and fatigue states. Findings agree with localized muscle fatigue literature, suggesting that with fatigue there is decreased impact transmission, which may protect the leg. The relative effects of leg stiffness and ankle angle on tibial response need to be verified.

Leg Tissue Mass Composition Affects Tibial Acceleration Response Following Impact

“…A human pendulum, consisting of a rectangular steel frame (190.5 cm × 52.5 cm) and canvas bed suspended from the ceiling by four steel cables (Flynn et al, 2004;Holmes & Andrews, 2006;Duquette & Andrews, 2010a, 2010b, was used to swing participants toward an impact apparatus, such that they impacted it with the unshod heel of their right foot. This type of apparatus has been used previously in the literature (Flynn et al, 2004;Duquette & Andrews, 2010a, 2010bLafortune & Lake, 1995;Lafortune et al, 1996aLafortune et al, , 1996b to maximize control over initial impact conditions, such that the impact forces and velocities produced are consistent with those encountered at heel strike during running (Cavanagh & Lafortune, 1980).…”

“…Peak acceleration, acceleration slope, and time to peak acceleration were determined from the tibial acceleration waveforms. Acceleration slope was measured between 30% and 70% of the peak acceleration (Flynn et al, 2004;Holmes & Andrews, 2006;Duquette & Andrews, 2010a, 2010b. Accelerometer signals were filtered close to the source with a fourth-order Bessel switched capacitor low-pass filter with a cut-off frequency of 1.5 Hz.…”

“…Two 5 cm wide nylon straps were placed across the pelvis and the distal thigh of the right leg to secure participants to the pendulum. The impact apparatus consisted of a vertically mounted force platform, anchored to a steel grid, which in turn was rigidly attached to the laboratory wall and floor (Flynn et al, 2004;Holmes & Andrews, 2006;Duquette & Andrews, 2010a, 2010b.…”

“…However, the tissues of the leg have often been treated as a singular mass and the individual contributions of the soft and rigid tissues to shock attenuation have not been established. Given the inherent differences in material properties between the tissues types, it is reasonable to assume that each may play a different role in attenuation, as measured in terms of their effect on tibial acceleration response parameters (e.g., peak acceleration, time to peak acceleration, acceleration slope) (Flynn et al, 2004;Holmes & Andrews, 2006;Duquette & Andrews, 2010a, 2010b. Furthermore, significant sex differences have been found in the magnitudes and proportions of these tissue masses (Lemieux et al, 1993;Ogle et al, 1995).…”

“…Previous work has shown that varying the levels of leg muscle activation at impact can affect shock wave attenuation through the leg (Flynn et al, 2004;Holmes & Andrews, 2006). It was proposed that higher levels of leg muscle activation increased muscle stiffness, which reduced the muscles' ability to dampen the impact shock wave and increased transmission to the proximal tibia.…”