Changes In Complexity At Maximal Speeds May Not Influence Functional Performance Immediately After: Pilot Study

Abstract

Regulatory statistics have been previously used to quantify nonlinear characteristics of gait and infer changes in central regulation of movement. Evaluating changes in movement complexity under varying running conditions is essential as alterations in central regulation may influence performance. However, few studies have characterized movement complexity during functional performance tests. PURPOSE: To quantify changes in complexity during an incremental running test to max speed, and during a single leg hop (SLH) test performed immediately before and after. METHODS: Seven healthy runners (25.8±4.9 yrs) performed a 30s SLH test before and after an incremental running test on a motorized treadmill using 4-minute stages (preferred, 10, 12, 14, 16, 18km/h) until volitional exhaustion. Three-dimensional accelerations of the pelvis were recorded using a triaxial accelerometer (100Hz, G-Walk, BTS Bioengineering, Milan, IT) fixed to the pelvis. The last 30s of each running speed and SLH were analyzed using multiscale entropy (MSE) across 5 time scales. Sample entropy estimates (m=2, r=.2) for each scaled time series were summed across all scales to compute complexity index (CI). Paired t-test were employed to compare CI measured from SLH tests and repeated measures ANOVAs with a Bonferroni correction were employed to compare differences in CI between stages for each participant. If significant, Dunnett’s test was employed to compare fastest and slowest stages with preferred. Vertical accelerations are reported. RESULTS: Testing was completed by runners as follows: stage 4 N=7, stage 5 N=5, stage 6 N=3. Mean differences in CI were significant for 4 of 7 runners (p<0.007). Post hoc analyses revealed greater CI in the final stage versus preferred (∆0.62±0.1; ∆1.11±0.01; ∆0.35±0.03; ∆0.49±0.07, p<0.01) while no differences were observed in the slowest stage. No change in SLH CI was found between pre- vs post-run tests (p=0.33, 2.25±0.9 vs 2.14±0.7). CONCLUSION: At maximal speeds, an increase in system adaptability was observed compared to preferred running, however, this increase was not transferred to functional performance immediately after. An increase in complexity during perturbed running and not hopping may be due to dissimilarities in task difficulty and constraint type experienced by the runners.