Neuromuscular responses to consecutive day military load carriage

Previous research has shown that lower limb peak torque (PT) is reduced up to 72 hours after treadmill load carriage. Peak torque measures can occur at a range of muscle lengths and as such are unable to define the changes in muscle function, which may occur because of load carriage. <br /><br />PURPOSE:<br />To determine changes in lower limb neuromuscular output, in responses to consecutive day military load carriage on a treadmill compared to an unloaded control group.<br /><br />METHODS<br />12 participants (10 males: 88.8 Kg ± 16.8 Kg, 188.72cm ± 8.5cm; 2 females: 63.4kg ± 12kg, 164.2 cm ± 8cm) walked on a level treadmill carrying 32kg across webbing, backpack and rifle, at a speed of 5.4km⋅h-1 for two hours on two consecutive days. 8 participants (6 males: 92.8 Kg ± 11.8 Kg, 187.22cm ± 8.5cm; 2 females: 64.2kg ± 12kg, 154.1 cm ± 8cm) completed the protocol without the military equipment. Neuromuscular output of the ankle and knee flexors and extensors were studied by observing changes in torque by isokinetic dynamometry. Knee extensor and flexor muscles were studied at 0, 60, 180 °⋅s-1. Ankle dorsi and plantar flexors were observed at 0, 60, 120 °⋅s-1. Measurements were taken pre and post load carriage on day one and day two. Torque was record as PT and at 5° intervals during isokinetic contraction.<br /><br />RESULTS<br />Statistically significant reductions in PT were observed post load carriage on day one and two in the dorsiflexors at 60 and 180°⋅s-1(P<0.05) and knee flexors and extensors at 60 and 0°⋅s-1 (P<0.05), these are supported by torque reductions throughout the movement (70° to 0°)(P<0.05). PT returned to baseline 24 hours post exercise while torque at serial muscle lengths remained reduced. No changes were observed between unloaded and loaded walking.<br /><br />CONCLUSION<br />Findings indicate that two hours of treadmill load carriage causes a bimodal change in neuromuscular function of the knee extensors and flexors and the ankle dorsiflexors, characterised by a reduction in the PT and torque over two days of repeated exercise. However, no significant difference was observed between loaded and unloaded groups. While temporal results find support in the previous literature, the inclusion of an exercising control group, that demonstrates no significant change, suggests that they fail to observe that load carriage causes no greater reduction in neuromuscular function than unloaded walking.