Introduction: 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. 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. Methods: Eleven 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. Results: There 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. Discussion: This 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.
The objective was to examine the interactive effects of load magnitude and locomotion pattern on lower-extremity joint angles and intralimb coordination in recruit-aged women. Twelve women walked, ran, and forced marched at body weight and with loads of +25%, and +45% of body weight on an instrumented treadmill with infrared cameras. Joint angles were assessed in the sagittal plane. Intralimb coordination of the thigh–shank and shank–foot couple was assessed with continuous relative phase. Mean absolute relative phase (entire stride) and deviation phase (stance phase) were calculated from continuous relative phase. At heel strike, forced marching exhibited greater (P < .001) hip flexion, knee extension, and ankle plantar flexion compared with running. At mid-stance, knee flexion (P = .007) and ankle dorsiflexion (P = .04) increased with increased load magnitude for all locomotion patterns. Forced marching (P = .009) demonstrated a “stiff-legged” locomotion pattern compared with running, evidenced by the more in-phase mean absolute relative phase values. Running (P = .03) and walking (P = .003) had greater deviation phase than forced marching. Deviation phase increased for running (P = .03) and walking (P < .001) with increased load magnitude but not for forced marching. With loads of >25% of body weight, forced marching may increase risk of injury due to inhibited energy attenuation up the kinetic chain and lack of variability to disperse force across different supportive structures.
Metabolic energy expenditure (MEE) is a primary determinant of gait, and joint loading may be as well. Externally loading an individual may require balancing these determinants when walking. PURPOSE:The purpose of this study was to investigate the effects of reducing vertical ground reaction forces (vGRF) through feedback on gross metabolic power. We hypothesized that reducing vGRF would come at the cost of greater MEE. METHODS: Twelve healthy participants (6 males [BMI = 22.19 ± 1.57]; 6 females [BMI = 20.12 ± 1.33]) between 20-25 years of age completed three 10-minute walking trials on an instrumented treadmill at 1.4 m•s -1 with no load, 15% body-weight (BW) and 30% BW (weighted vest). The participants received no feedback for the first five minutes, then during the second five minutes, they were told to lower peak vertical ground reaction forces based on visual feedback of those forces. Expired gases were collected to estimate MEE using the Brockway equation, then normalized by body mass (BM) and body mass plus external load (BMEL). A 2-way ANOVA (p < 0.05) was used to compare main effects of feedback and load for each of the load normalizations. RESULTS:The feedback conditions had significantly greater MEE than no feedback across the different loads (p < 0.001) for both normalization methods (Fig 1). The MEE increased significantly with greater loads for feedback and no-feedback with BM normalization (p < 0.001) but did not differ significantly with BMEL normalization (p = 0.177) (Fig 1). CONCLUSION: As participants tried to lower peak vertical ground reaction forces, MEE increased, suggesting an interaction of loads and MEE while walking. Similar to previous studies, MEE increases when deviating from preferred gait mechanics. We found that when accounting for the BMEL, MEE decreased as external load increased, that is opposite to BM normalization alone. Including BMEL may allow better understanding about how we metabolically accommodate to increasing loads.
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