Carbohydrate vs protein supplementation for recovery of neuromuscular function following prolonged load carriage

Abstract

Background: This study examined the effect of carbohydrate and whey protein supplements on recovery of neuromuscular function after prolonged load carriage.

Methods: TEN MALE PARTICIPANTS (BODY MASS: 81.5 +/- 10.5 kg, age: 28 +/- 9 years, O(2)max: 55.0 +/- 5.5 ml.kg(-1).min(-1)) completed three treadmill walking tests (2 hr, 6.5 km.h(-1)), carrying a 25 kg backpack consuming 500 ml of either: (1) Placebo (flavoured water) [PLA], (2) 6.4% Carbohydrate Solution [CHO] or (3) 7.0% Whey Protein Solution [PRO]. For three days after load carriage, participants consumed two 500 ml supplement boluses. Muscle performance was measured before and at 0, 24, 48 and 72 h after load carriage, during voluntary and electrically stimulated contractions.

Results: Isometric knee extension force decreased immediately after load carriage with no difference between conditions. During recovery, isometric force returned to pre-exercise values at 48 h for CHO and PRO but at 72 h for PLA. Voluntary activation decreased immediately after load carriage and returned to pre-exercise values at 24 h in all conditions (P = 0.086). During recovery, there were no differences between conditions for the change in isokinetic peak torque. Following reductions immediately after load carriage, knee extensor and flexor peak torque (60 degrees .s(-1)) recovered to pre-exercise values at 72 h. Trunk extensor and flexor peak torque (15 degrees .s(-1)) recovered to pre-exercise values at 24 h (P = 0.091) and 48 h (P = 0.177), respectively.

Conclusion: Recovery of neuromuscular function after prolonged load carriage is improved with either carbohydrate or whey protein supplementation for isometric contractions but not for isokinetic contractions.

Figure 1

Force of the knee extensors during isometric MVC. Measurements were made before and after (0, 24, 48 and 72 h) 120 minutes of treadmill walking at 6.5 km·h^-1 (n = 10) on a level gradient (0%) carrying a 25 kg backpack with consumption of 250 ml (at 0 and 60 minutes) of a beverage containing placebo (PLA - Black square), carbohydrate (6.4%) (CHO - Black triangle) or protein (7%) (PRO - Black circle) and twice daily (500 ml, morning and evening) for the 3 days after load carriage (n = 10). Symbols show difference from pre measurement for PLA (* P < 0.05), CHO († P < 0.05), PRO (# P < 0.05).

Figure 2

Peak torque of the knee extensors during isokinetic contractions (60°·s^-1). Measurements were made before and after (0, 24, 48 and 72 h) 120 minutes of treadmill walking at 6.5 km·h^-1 (n = 10) on a level gradient (0%) carrying a 25 kg backpack with consumption of 250 ml (at 0 and 60 minutes) of a beverage containing either placebo (PLA - Black square), carbohydrate (6.4%) (CHO - Black triangle) or protein (7%) (PRO - Black circle) and twice daily (500 ml, morning and evening) for the 3 days after load carriage (n = 10). Symbols show difference from pre measurement for PLA (* P < 0.05), CHO († P < 0.05), PRO (# P < 0.05).

Figure 3

Peak torque of the knee flexors during isokinetic contractions (60°·s^-1) Measurements were made before and after (0, 24, 48 and 72 h) 120 minutes of treadmill walking at 6.5 km·h^-1 (n = 10) on a level gradient (0%) carrying a 25 kg backpack with consumption of 250 ml (at 0 and 60 minutes) of a beverage containing either placebo (PLA - Black square), carbohydrate (6.4%) (CHO - Black triangle) or protein (7%) (PRO - Black circle) and twice daily (500 ml, morning and evening) for the 3 days after load carriage (n = 10). Symbols show difference from pre measurement for PLA (* P < 0.05), CHO († P < 0.05), PRO (# P < 0.05).

Figure 4

Peak torque of the trunk flexors during isokinetic contractions (15°·s^-1). Measurements were made before and after (0, 24, 48 and 72 h) 120 minutes of treadmill walking at 6.5 km·h^-1 (n = 10) on a level gradient (0%) carrying a 25 kg backpack with consumption of 250 ml (at 0 and 60 minutes) of a beverage containing either placebo (PLA - Black square), carbohydrate (6.4%) (CHO - Black triangle) or protein (7%) (PRO - Black circle) and twice daily (500 ml, morning and evening) for the 3 days after load carriage (n = 10). Symbols show difference from pre measurement for PLA (* P < 0.05), CHO († P < 0.05), PRO (# P < 0.05).