Effect Of Protein Supplementation On Dietary Intake, Muscle Function And Soreness During Military Field Exercise

PURPOSE: Military training can result in negative energy balance, low energy availability (≤ 30 kcal·kg FFM-1·d-1), negative protein balance and muscle damage. This study investigated the effect of a high protein dietary supplement on ad libitum energy and macronutrient intake, muscle function and muscle soreness, during an arduous military field exercise. METHODS: Thirty male British Army Officer Cadets were randomly assigned to a control (CON; n = 15, mean ± SD; age 23 ± 2 y, body mass 80.8 ± 6.6 kg) or supplementation group (SUP; n = 15, age 25 ± 3 y, body mass 84.4 ± 12.5 kg). Both groups consumed food ad libitum during a 2-day field exercise and a 4-day post-exercise recovery period. SUP were also provided two protein-rich bars (434 kcal, 46.6 g protein, 27.2 g carbohydrate and 16.4 g fat) per day during field exercise and recovery. Energy expenditure was estimated using a tri-axial accelerometer and energy intake was estimated from food diaries and food wrappers. Isometric mid-thigh pull force, isokinetic knee extension/flexion peak torque, and muscle soreness and perceived fatigue were measured at baseline, and after field exercise and recovery. RESULTS: For energy balance and energy availability there was a main effect of time, but no group or group x time interaction, where participants were in greater negative energy balance (CON: −3717 ± 687, SUP: −3638 ± 1194 kcal·d-1) and lower energy availability (CON: −30 ± 8, SUP: −21 ± 16 kcal·kg FFM-1·d-1) during field exercise. Protein intake was greater in SUP compared to CON during field exercise (CON: 56 ± 22, SUP: 105 ± 30 g·d-1; p < 0.001) and recovery (CON: 125 ± 37 vs. SUP: 161 ± 35 g·d-1; p < 0.05) as desired. Isometric knee extension at a velocity of 180 °/s was 6% greater during recovery than during FEX only, but with no difference between groups. There was no significant difference in any other muscle function measures between conditions or group (all p > 0.05). Muscular soreness and fatigue were increased after FEX (p < 0.05), irrespective of group (p > 0.05). CONCLUSIONS: The provision of a high protein dietary supplement during a military field exercise increased protein intake, but did not attenuate the energy deficit or improve muscle function or soreness.