Effect of localized muscle fatigue on vertical ground reaction forces and ankle joint motion during running
Introduction
Muscle fatigue has been hypothesized to be a causative factor in many running injuries (Baker, Frankel, & Burnstein, 1972; Burr, 1997; Dickinson, Cook, & Leinhardt, 1985; Grimston & Zernike, 1993; Nyland, Shapiro, Stine, Horn, & Ireland, 1994). Nordin and Frankel (1989) theorized that intense, strenuous running leads to fatigued muscle, resulting in changes to the muscle's shock absorbing capability and/or changes in running mechanics. Excessive impact forces and/or loading rate and abnormal ankle joint motion are thought to play a major role in running injuries (Nigg, Cole, & Brüggemann, 1995). While there are several mechanisms by which impact loading during running may be attenuated, muscle contraction in association with joint motion, is the mechanism largely affected by localized muscle fatigue (Radin, 1986). Presently, there are few studies demonstrating the effect of localized muscle fatigue on measures related to lower limb loading during running.
Experiments involving exhaustive running have shown that with the onset of general fatigue, there tends to be a decrease in dorsiflexion at heel contact, and an increase in rearfoot motion (Dutto, Levy, Lee, Sidthalaw, & Smith, 1997; Elliott & Ackland, 1981; Gheluwe & Madsen, 1997). The literature is contradictory as to the effects of exhaustive running on the ground reaction forces (Brüggemann & Arndt, 1994; Dickinson et al., 1985). The impact force has been reported to increase (Dickinson et al., 1985) or to decrease (Brüggemann & Arndt, 1994) following fatiguing treadmill runs. In a recent study, peak tibial accelerations were shown to increase when a fatigued state was achieved by a runner (Verbitsky, Mizrahi, Voloshin, Treiger, & Isakov, 1998). In dogs, peak tibial strains have been shown to increase following fatiguing exercise (Yoshikawa et al., 1994). Exhaustive running protocols, however, fail to distinguish which kinematic or kinetic changes are a direct result of localized muscle fatigue. The changes resulting from localized muscle fatigue may lead to abnormal loading and, in turn, altered stress distribution to internal structures. Localized muscle fatigue protocols have been used to examine the effects of plantar flexor and dorsiflexor fatigue on postural sway, and the effects of quadriceps and hamstring fatigue on the kinematics and kinetics of crossover cutting (Lundin, Feuerbach, & Grabiner, 1993; Nyland, Shapiro, Caborn, Nitz, & Malone, 1997). To our knowledge, no studies have investigated the effects of localized muscle fatigue on the ankle joint motion and ground reaction forces during the impact phase of running.
Direct dynamics simulation techniques have been used to model the impact phase of running. These simulations have shown that the selection of initial conditions (muscle co-contraction and joint angles) has a large effect on the impact force and rate of rise of the impact force (Bobbert, Yeadon, & Nigg, 1992; Cole, Nigg, van den Bogert, & Gerritsen, 1996; Gerritsen, van den Bogert, & Nigg, 1995). Gerritsen et al. (1995) reported that decreasing the initial angle of the foot with respect to the ground at heel contact resulted in an increased impact force and a corresponding increase in loading rate. The authors concluded that by increasing the foot angle at heel contact, greater lengthening of the tibialis anterior could take place as the foot is lowered (an eccentric contraction). This would help to decrease the impact force by potentially allowing for greater energy absorption. Although caution must be exercised when interpreting the simulation results because of assumptions made in the model, it seems reasonable that with increasing levels of muscle fatigue, the dorsiflexors may lose some of their ability to act eccentrically, thereby resulting in an increase in ground reaction force.
The relationships between initial rearfoot angle at touchdown, maximum eversion and the loading rate and magnitude of the impact force have primarily been studied using shoe alterations or mechanical modeling (Perry & Lafortune, 1995; Stacoff, Denoth, Kaelin, & Stuessi, 1988). While prevention of normal maximum eversion using a varus wedge has been shown to result in an increase in the magnitude and loading rate of the impact force, exaggeration of maximal eversion using a valgus wedge resulted in no change in impact loading (Perry & Lafortune, 1995). Using a two-dimensional mechanical model, Stacoff et al. (1988) found that decreasing the lever arm between the ground reaction force at touchdown and the subtalar joint center (in the frontal plane) resulted in an increased peak impact force and loading rate. Invertor fatigue may result in a decrease in the length of this lever at touchdown and a resultant increase in the impact loading.
Electromyographic studies of tibialis anterior and tibialis posterior (the primary dorsiflexor and invertor of the foot, respectively) have shown that these muscles are active for 50–85% of the running cycle suggesting a high probability for fatigue (Reber, Perry, & Pink, 1993), particularly in the early stages of training. Localized fatigue may lead to muscle torque imbalances about the ankle, resulting in changes in the initial joint position at touchdown (rearfoot and/or sagittal), and the corresponding ground reaction force. Decreased force production or change in timing due to fatigue of tibialis anterior and/or tibialis posterior may also contribute to excessive rearfoot motion during the early to midstance phase (Cornwall & McPoil, 1994; Elliott & Blanksby, 1979). Given that both extreme values of maximum eversion and unattenuated impact forces have been postulated to play major roles in running injuries (James & Jones, 1990; Nigg et al., 1995), the role of localized muscle fatigue on these measures, independent of general fatigue effects, should be examined.
The purpose of this study was to examine the effects of localized muscle fatigue on the vertical ground reaction forces (VGRFs) and ankle joint motion seen during the first 50% of the stance phase of running. It was hypothesized that localized fatigue of the invertor muscle group (tibialis posterior, flexor digitorum longus, flexor hallucis longus, tibialis anterior and extensor hallucis longus) would result in increased maximum eversion, as well as decreased dorsiflexion and inversion at heel strike causing an increase in the impact force and the rate of rise of the impact force. Further, it was hypothesized that localized fatigue of the dorsiflexor muscle group (tibialis anterior, extensor hallucis longus, peroneus tertius and extensor digitorum longus) would result in decreased dorsiflexion at heel contact, increased rate of rise of the impact force, and increased peak impact force.
Section snippets
Subjects
Eleven female recreational runners (age=24.3±3.5 years; mass=60.8±9.5 kg) from the University community volunteered to participate in the study. All subjects were heel-strike runners and had no history of surgical intervention, chronic pain, orthotic use or current pathology of the lower extremity. All subjects provided written informed consent as stipulated by the University Human Subjects Review Committee.
Protocol
Subjects were videotaped and VGRFs were collected while running on a force measuring
Torque output of dorsiflexors and invertors
All post-run maximum isometric torques were significantly (p⩽0.01) less than the initial, pre-fatigue maximum. After the fatigue protocol for dorsiflexors, the maximum isometric torque dropped to 57.6%±10.6% of the initial, pre-fatigue maximum (Fig. 3(a)). The average dorsiflexor torque increased following the post-fatigue treadmill run, but was still significantly less (p⩽0.01) than the initial maximal torque immediately after the run (76.7%±10.7%), 5 minutes after the run (80.2%±8.2%), and 10
Discussion
The aim of this study was to evaluate the effects of localized, lower limb muscle fatigue on the ankle joint motion and VGRF during running. Fatiguing exercise of the dorsiflexors resulted in an increased loading rate of the impact force and decreased dorsiflexion at heel strike, which agrees with our hypothesis. The impact peak magnitudes remained unaffected. Contrary to our expectations, no rearfoot parameters were changed by dorsiflexor fatigue. Virtually all of the kinetic and kinematic
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2022, Gait and PostureCitation Excerpt :Initial research has shown kinematic and kinetic differences induced by fatigue during a prolonged run [29–32]. Runners with rearfoot FP in an exhaustive fatigue condition experienced increased knee flexion [19,32], foot dorsiflexion [26], and foot eversion angles compared to their resting state [19,32,33]. However, regular training runs below anaerobic threshold do not require a near volitional exhaustion effort.