Protein Supplementation Does Not Augment Adaptations to Endurance Exercise Training

Jonvik KL, Paulussen KJM, Danen SL, Ceelen IJM, Horstman AM, Wardenaar FC, VAN Loon LJC, VAN Dijk JW. Med Sci Sports Exerc. 2019 Oct;51(10):2041-2049. doi: 10.1249/MSS.0000000000002028.

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Take-Home Message

People performing a 12-week endurance training program with protein supplementation had similar improvements in maximal oxygen uptake and performance as people training and consuming a placebo drink.


An athlete can use protein supplementation after resistance training to augment strength and muscle mass gains.  Endurance athletes are also increasingly using protein supplementation after exercise to improve their performance. However, it remains unclear if protein supplements help improve a person’s endurance during training. These authors conducted a double-blind, randomized, placebo-controlled trial to see if frequent protein supplementation during 12 weeks of endurance training would improve maximal oxygen uptake and endurance performance. The authors randomly assigned 60 nonobese males into 2 groups: protein group and placebo group. Before the beginning of a 12-week training protocol, each participant performed a maximum oxygen uptake test (VO2max), muscle function test, 10-kilometer time trial, and dual-energy x-ray absorptiometry to determine lean mass. During the 12-week program, each participant exercised on a cycle ergometer 3 times/week during supervised training sessions (Mondays, Wednesdays, and Fridays). Each Monday, the participants performed a 6 x 4-minute interval at 85%-90% heart rate max with 4-minute active recoveries. Each Wednesday, the participants completed one 60 minute cycle at 75%-80% heart rate max. Each Friday, the participants performed three sets of 6 x 1-minute work intervals at 90%-95% heart rate max with an active recovery period between each repetition and set. After each training session and 15 minutes before bedtime each participant consumed 250 mL of either protein or carbohydrate placebo drink. The protein drink contained 28.7 g protein, while the carbohydrate placebo drink contained 25.8 g carbohydrate.

Four participants in the placebo group withdrew from testing due to injuries or personal reasons. At the end of the 12-week regime, the groups had similar maximum oxygen uptake, performance on a time trial, and muscular endurance. However, the researchers noticed that the protein group may have experienced slightly greater improvement in leg lean mass than the placebo group.


Overall, this study is interesting because it demonstrates that an athlete who is trying to increase their maximal oxygen uptake and performance in cycling does not need to supplement with protein. More and more athletes are trying protein supplementation to augment their training; but, this study offers compelling evidence that there may be no added benefit for endurance athletes. However, it is unclear if these findings apply to endurance athletes in different sports (e.g., runners or swimmers). Furthermore, it is unclear if protein supplementation would help an athlete who does endurance and resistance training. We need more studies like this well-controlled trial to help us teach our athletes about the benefits/harms of various supplements they are trying. Clinicians should work with coaches and athletes to decide if protein supplementation has a role in their training plan.

Questions for Discussion

What are your thoughts on protein supplementation in an athlete who trains strictly aerobically? Do you think the result would have been different if the researchers paired their endurance training with resistance training?

Written by: Daniel Webb
Reviewed by: Jeffrey Driban

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