Abstract
IntroductionDuring cyclical steady state ambulation, such as walking, variability in stride intervals can indicate the state of the system. In order to define locomotor system function, observed variability in motor patterns, stride regulation and gait complexity must be assessed in the presence of a perturbation. Common perturbations, especially for military populations, are load carriage and an imposed locomotion pattern known as forced marching (FM). We examined the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and gait complexity during bipedal ambulation in recruit-aged females.MethodsEleven healthy physically active females (18–30 years) completed 1-min trials of running and FM at three load conditions: no additional weight/bodyweight (BW), an additional 25% of BW (BW + 25%), and an additional 45% of BW (BW + 45%). A goal equivalent manifold (GEM) approach was used to assess motor variability yielding relative variability (RV; ratio of “good” to “bad” variability) and detrended fluctuation analysis (DFA) to determine gait complexity on stride length (SL) and stride time (ST) parameters. DFA was also used on GEM outcomes to calculate stride regulation.ResultsThere was a main effect of load (p = 0.01) on RV; as load increased, RV decreased. There was a main effect of locomotion (p = 0.01), with FM exhibiting greater RV than running. Strides were regulated more tightly and corrected quicker at BW + 45% compared (p < 0.05) to BW. Stride regulation was greater for FM compared to running. There was a main effect of load for gait complexity (p = 0.002); as load increased gait complexity decreased, likewise FM had less (p = 0.02) gait complexity than running.DiscussionThis study is the first to employ a GEM approach and a complexity analysis to gait tasks under load carriage. Reduction in “good” variability as load increases potentially exposes anatomical structures to repetitive site-specific loading. Furthermore, load carriage magnitudes of BW + 45% potentially destabilize the system making individuals less adaptable to additional perturbations. This is further evidenced by the decrease in gait complexity, which all participants demonstrated values similarly observed in neurologically impaired populations during the BW + 45% load condition.
Highlights
During cyclical steady state ambulation, such as walking, variability in stride intervals can indicate the state of the system
Load had a significant influence on relative variability reducing the number of successful or “good” movement solutions, exemplified as relative variability magnitude decreasing as load magnitude increased confirmed by the main effect of load (F2,20 = 5.50, p = 0.01, η2P = 0.36); with post hoc analysis revealing BW + 45% (1.28 ± 0.05) being significantly (p = 0.02) less than BW (1.55 ± 0.07)
Only a single subject demonstrated an “Impaired” classification at baseline (RN at BW). This participant trained for the shortest durations (30 min maximum) only 2–3 times a week. The objectives of this investigation were to determine the interactive effects of load magnitude and locomotion pattern on motor variability, stride-to-stride control/regulation and complexity
Summary
During cyclical steady state ambulation, such as walking, variability in stride intervals can indicate the state of the system. In order to define locomotor system function, observed variability in motor patterns, stride regulation and gait complexity must be assessed in the presence of a perturbation. Especially for military populations, are load carriage and an imposed locomotion pattern known as forced marching (FM). We examined the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and gait complexity during bipedal ambulation in recruit-aged females. Bipedal ambulation requires the complex integration of multisensory information (optical, somatic and vestibular) that is used to coordinate actions within specific environments in order to achieve goal-directed movement (Alexander, 1992; Warren et al, 2001; Bent et al, 2004a; Pandy and Andriacchi, 2010; Matthis et al, 2017). Measuring the responses of biomechanical variables to the perturbation of additional loading during locomotory tasks provides valuable insight to the global functional state of the locomotor system
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