Abstract
Background and Purpose: Human locomotion requires characteristic muscle activation timing patterns that work in a defined fashion along a kinetic chain. Sling systems are chains of muscles and innervating fascia that facilitate sequential muscle activation patterns during movement. The purpose of this study was to examine four sling systems across a running gait cycle and to determine how they might differ between runners with high and low running economy. Participants: Twenty-five recreational runners (11M, 14F, height = 1.73 ± .07 m, mass = 70.3 ± 11.7 kg, age = 28.6 ± 5.1 years) completed this study. Methods: Recreational runners completed a running economy test and were classified as high economy or low economy based on published normative data. On a separate testing day, runners completed overground running trials at a 10-km race pace and slow running pace. Surface electromyography was used to measure muscle activation during run trials for four sling systems: the Posterior Oblique Sling (POS: gluteus maximus and contralateral latissimus dorsi), the Anterior Oblique Sling (AOS: external oblique and contralateral adductors), the Lateral Sling (LAT: gluteus medius, tensor fascia latae (TFL), and contralateral quadratus lumborum (QL)), and the Deep Longitudinal Sling (LONG: tibialis anterior (TA), peroneus longus, biceps femoris (BF), multifidus, and erector spinae (ES)). Mixed-Design ANOVAs were conducted to determine differences among sling systems and between groups in muscle onset time (EMGonset), muscle offset time (EMGoffset), peak amplitude (EMGamp), and time of peak amplitude (EMGpeak). Peak times and amplitudes for the muscles of the AOS could not be established as these muscles displayed nearly constant activation throughout the gait cycle. Results: Significant main effects were observed in the POS, LONG, and LAT at both the 10-km race pace and slow running pace for EMGonset, EMGoffset, EMGpeak, and EMGamp. Differences between high economy and low economy runners were observed for ES EMGonset Burst 3, ES EMGpeak Burst 3, ES EMGamp Burst 3,BF EMGonset Burst 1, BF EMGpeak Burst 1, BF EMGoffset Burst 2, BF EMGpeak Burst 2, BF EMGpeak Burst 3, BF EMGamp Burst 1, and TA EMGpeak at the slow running speed. At the 10-km race pace, differences between high economy and low economy runners were observed for TFL EMGonset Burst 2, QL EMGoffset Burst 1, QL EMGpeak Burst 2, and QL EMGonset Burst 3. Discussion and Conclusion: Muscles in the POS, LAT, and LONG work in defined sequential and synchronous patterns across the gait cycle with significant variability between high economy and low economy runners.