Human locomotion requires characteristic muscle activation timing patterns that work in a defined fashion along a kinetic chain. Sling systems are chains of global muscles and their innervating fascia that facilitate sequential muscle activation patterns during movement.
PURPOSE: To examine muscle activation patterns as they differ between high economy (HI) and low economy (LO) runners in three sling systems.
METHODS: Recreational runners (11M, 14F, height 1.73 ± .07 m, mass 70.3 ± 11.7 kg, age 28.6 ± 5.1 y) completed a running economy test and were classified as HI or LO. Runners completed overground running trials at a 10K race pace. Muscle activation patterns of three sling systems, the Posterior Oblique Sling (POS: gluteus maximus, contralateral latissimus dorsi), the Lateral Sling (LAT: gluteus medius, tensor fascia latae (TFL), contralateral quadratus lumborum (QL)), and the Deep Longitudinal Sling (DLS: tibialis anterior (TA), peroneus longus, biceps femoris (BF), multifidus, erector spinae (ES)) were measured during run trials using electromyography. Mixed-Design ANOVAs were conducted to determine differences among sling systems and between groups in muscle onset time (ON), muscle offset time (OFF), peak amplitude (AMP), and time of AMP (PEAK).
RESULTS: Significant main effects were seen in the POS for ON (F(2,46) = 104.72, p < .001), OFF (F(2,46) = 151.43, p < .001), PEAK (F(2,46) = 69.472, p < .001), and AMP (F(2,46) = 18.885, p < .001); in the LAT for ON (F(7,140) = 300.68, p < .001), OFF (F(7,140) = 414.76, p < .001), PEAK (F(7,140) = 382.54, p < .001), and AMP (F(7,140) = 20.38, p < .001); and in the DLS for ON (F(10,210) = 469.99, p < .001), OFF (F(10,210) = 303.29, p < .001), PEAK (F(10,210) = 237.18, p < .001), and AMP = (F(10,210) 10.03, p < .001). Differences between HI and LO were seen for QL ON (F(1,23) = 11.04, p = .003), QL PEAK (F(1,23) = 5.24, p = .032), TFL ON (F(1,23) = 5.14, p = .033), ES ON (F(1,23) = 4.93, p = .037), ES PEAK (F(1,23) = 4.59, p = .043), ES AMP (F(1,23) = 5.04, p = .035), BF OFF (F(1,20) = 8.79, p = .008), BF PEAK (F(1,20) = 10.09, p = .005), BF OFF (F(1,23) = 7.27, p = .013), BF AMP (F(1,20) = 6.39, p = .020), and TA PEAK (F(1,23) = 5.59, p = .027).
CONCLUSION: Muscles in the sling systems work in defined sequential patterns across the gait cycle with significant variability between HI and LO runners.