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Unexpected perturbations during locomotion can occur during daily life or sports performance. Adequate compensation for such perturbations is crucial in maintaining effective postural control. Studies utilising instrumented treadmills have previously validated perturbed walking protocols, however responses to perturbed running protocols remain less investigated. Therefore, the purpose of this study was to investigate the feasibility of a new instrumented treadmill-perturbed running protocol. <br /> Fifteen participants (age = 2 8 +/- 3 years; height = 172 +/- 9 cm; weight = 69 +/- 10 kg; 60% female) completed an 8-minute running protocol at baseline velocity of 2.5 m/s (9 km/h), whilst 15 one-sided belt perturbations were applied (pre-set perturbation characteristics: 150 ms delay (post-heel contact); 2.0 m/s amplitude; 100 ms duration). Perturbation characteristics and EMG responses were recorded. Bland-Altman analysis (BLA) was employed (bias +/- limits of agreement (LOA; bias +/- 1.96*SD)) and intra-individual variability of repeated perturbations was assessed via Coefficients of Variation (CV) (mean +/- SD). <br /> On average, 9.4 +/- 2.2 of 15 intended perturbations were successful. Perturbation delay was 143 +/- 10 ms, amplitude was 1.7 +/- 0.2 m/s and duration was 69 +/- 10 ms. BLA showed -7 +/- 13 ms for delay, -0.3 +/- 0.1 m/s for amplitude and -30 +/- 10 ms for duration. CV showed variability of 19 +/- 4.5% for delay, 58 +/- 12% for amplitude and 30 +/- 7% for duration. EMG RMS amplitudes of the legs and trunk ranged from 113 +/- 25% to 332 +/- 305% when compared to unperturbed gait. This study showed that the application of sudden perturbations during running can be achieved, though with increased variability across individuals. The perturbations with the above characteristics appear to have elicited a neuromuscular response during running.
BACKGROUND: Compensating unstable situations is an important functional capability to maintain joint stability, to compensate perturbations and to prevent (re-)injury. Therefore, reduced maximum strength and altered neuromuscular activity are expected by inducing instability to load test situations. Possible effects are not clear for induced instability during maximum legpress tests in healthy individuals. OBJECTIVE: To compare isokinetic legpress (LP) strength and lower-leg muscle activity using stable (S) and unstable (UN) footplates. METHODS: 16 males (28 +/- 4 yrs, 179 +/- 7 cm, 75 +/- 8 kg) performed five maximum LP in concentric (CON) and eccentric (ECC) mode. The maximum force (Fmax) and muscle activity were measured under conditions of S and UN footplates. The tested muscles comprised of the tibialis anterior (TA), peroneus longus (PL) and soleus (SOL) and their activity were quantified against the MVIC of each muscle respectively. RESULTS: The main finding revealed a significant reduction in Fmax under UN condition: 11.9 +/- 11.3% in CON and 23.5 +/- 47.8% in ECC (P < 0.05). Significant findings were also noted regarding the RMS derived values of the EMG of PL and TA. CONCLUSION: Unstable LP reduced force generation and increased the activity of PL and TA muscles which confirmed greater neuromuscular effort to compensate instability. This may have some implications for resistance testing and training coupled with an unstable base in the prevention and rehabilitation of injury to the neuromusculoskeletal system.