Protein Supplementation Throughout 10 Weeks of Progressive Run Training Is Not Beneficial for Time Trial Improvement

Abstract

Introduction: Protein supplementation is proposed to promote recovery and adaptation following endurance exercise. While prior literature demonstrates improved performance when supplementing protein during or following endurance exercise, chronic supplementation research is limited. Methods: Runners (VO₂peak = 53.6 ± 8.9 ml/kg/min) were counter-balanced into a placebo group (PLA; n = 8) or protein group (PRO; n = 9) based on sex and VO₂peak, and underwent 10 weeks of progressive endurance training. Prior to training, body composition, blood cell differentials, non-invasive mitochondrial capacity using near-infrared spectroscopy, and a 5 km treadmill time trial (TT) were evaluated. Progressive training then commenced (5-10% increase in weekly volume with a recovery week following 3 weeks of training) whereby PRO supplemented with 25 g of whey protein following workouts and prior to sleep (additional 50 g daily). PLA supplemented similarly with a < 1 g sugar pill per day. Following training, participants were reanalyzed for the aforementioned tests. Results: VO₂peak and initial 5 km TT were not significantly different between groups. PRO consumed significantly more dietary protein throughout the training period (PRO = 132 g/d or 2.1 g/kg/day; PLA = 84 g/d or 1.2 g/kg/day). Running volume increased significantly over time, but was not significantly different between groups throughout training. Blood measures were unaltered with training or supplementation. Mitochondrial capacity trended toward improving over time (time p = 0.063) with no difference between groups. PLA increased lean mass 0.7 kg (p < 0.05) while PRO experienced infinitesimal change (-0.1 kg, interaction p = 0.049). PLA improved 5 km TT performance 6.4% (1 min 31 s), while PRO improved only 2.7% (40 s) (interaction p = 0.080). Conclusion: This is the first evidence to suggest long-term protein supplementation during progressive run training is not beneficial for runners.

Keywords: 5 km time trial; NIRS; endurance; lean body mass; mitochondrial capacity; run training; running; whey protein.

Figure 1

Training data represented as mean ± SD. “G” = group effect p-value, “T” = time effect p-value, “G×T” = group × time interaction p-value. (A) Average distance (km) run per week for the placebo group (PLA; gray) and protein group (PRO; black). There was not a significant group by time interaction or group effect (p > 0.05), however, there was a time effect (p < 0.05) whereby pairwise comparisons determined a significant difference between week 1 and weeks 6, 7, 8, and 9 (“§”, p < 0.05). (B) Average hours spent running per week for each group. A significant time effect existed (p < 0.05) whereby pairwise comparisons determined differences between week 1 and weeks 6, 7, 8, and 9 (“§”, p < 0.05). (C) Average pace for each group was not significantly different (p>0.05). Volume was increased weeks 1–3, 5–7, and 9, and weeks 4 and 8 were recovery weeks. Week 10 was a taper leading into post testing. Forced independent t-tests were conducted at each time point to determine any possible group differences and revealed no significant differences (p > 0.05).

Figure 2

Body composition data represented as mean ± SD. “G” = group effect p-value, “T” = time effect p-value, “G×T” = group × time interaction p-value, “d” = Cohen's d-value. (A) The left plot represents average mass (kg) in the placebo (PLA) and protein (PRO) groups at Pre (black bars) and Post (gray bars). The right plot represents individual participant data points for each group from Pre (circle) to Post (square). A time effect approached significance (p = 0.052). (B) The left plot represents average lean mass (kg) in each group. A significant interaction was found (p = 0.049). Pairwise comparisons determined a significant increase from pre to post for PLA (“*” p < 0.05). Cohen's d-value also demonstrated a large effect between groups (d = 1.032). The right plot represents individual participant data points for each group. (C) The left plot represents average fat mass (kg) in each group. A significant group effect was demonstrated (p = 0.016) showing greater fat mass in PLA than PRO. A significant time effect was also found (p = 0.006) showing a reduction in fat mass from Pre to Post. The right plot represents individual participant data points for each group.

Figure 3

Mitochondrial capacity data represented as mean ± SD. “G” = group effect p-value, “T” = time effect p-value, “G×T” = group × time interaction p-value, “d” = Cohen's d-value. The left plot represents mitochondrial capacity (rate constant, min⁻¹) in the placebo (PLA) and protein (PRO) groups at Pre (black bars) and Post (gray bars). A time effect (Post>Pre; p = 0.063) approached significance. The right plot represents individual participant data points for each group from Pre (circle) to Post (square).

Figure 4

5 km TT data represented as mean ± SD. “G” = group effect p-value, “T” = time effect p-value, “G×T” = group × time interaction p-value, “d” = Cohen's d-value. The left plot represents average time to run 5 km in the placebo (PLA) and protein (PRO) groups at Pre (black bars) and Post (gray bars). The middle plot represents individual participant data points for each group from Pre (circle) to Post (square). The right plot represents average percent change from Pre to Post for PLA (circle) and PRO (square). There was a significant time effect from Pre to Post (p < 0.001) demonstrating an improvement in time to completion. The group × time interaction approached significance (p = 0.080), and the Cohen's d-value also demonstrated a large effect between groups (d = 0.945).