Neuromuscular function following prolonged load carriage on level and downhill gradients

Decrements in muscle function may reduce physical and skilled performance and have been shown to be greater following walking unloaded on negative gradients. We examined the effects of prolonged walking with load carriage at level and negative gradients on muscle function.

There were 10 male participants who completed two bouts of load carriage carrying a 25-kg backpack for 2 h at 6.5 km x h(-1) during level walking (LW) and downhill (-8% gradient) walking (DW). Force produced during voluntary and electrically stimulated contractions was measured before, 0, 24, 48, and 72 h post-exercise.

Isometric knee extension force decreased immediately after LW (15 +/- 11%) and DW (16 +/- 17%) and recovered to baseline at 72 h. Voluntary activation decreased immediately after LW (95 +/- 5 to 91 +/- 10%) and DW (97 +/- 4 to 94 +/- 12%) and returned to baseline at 24 h. Electrically stimulated 20:50 Hz tetani decreased after LW and DW, with complete recovery by 24 h after DW only. LW and DW caused decreases immediately after exercise in isokinetic peak torque of knee extensors and flexors at 60 degrees x s(-1) and 180 degrees x s(-1), trunk extensors and flexors at 15 degrees x s(-1), and shoulder flexors at 60 degrees x s(-1), with complete recovery at different time points, but all by 72 h.

Level and downhill treadmill walking with load carriage resulted in similar changes in muscle function of the lower and upper body muscles immediately after exercise and during recovery. The decrements in muscle function may increase the risk of musculoskeletal injury and is likely to impair performance during physical and skilled tasks following load carriage.