Additional proteins could help endurance athletes


Endurance athletes who follow an intensive training programme and consume additional proteins show better progress through training than endurance athletes who do not consume additional proteins. This is the conclusion of Pim Knuiman’s PhD research in the Human Nutrition and Health group.

Knuiman made his findings through a study of 44 healthy young men, all of whom are recreational athletes. During a period of ten weeks, they exercised three times a week on an ergocycle (a kind of stationary exercise bike) at an intensity where they just avoided reaching complete acidification.

‘That intensity is often called the anaerobic or lactate threshold’, Knuiman explains. Half of the subjects were given additional proteins on top of their normal diet during the test period: after every workout and before going to bed, they ingested a drink containing 28 grams of casein protein. The other half – the control group – were given a protein-free carbohydrate drink that looked and tasted the same. Neither the athletes nor the researchers knew who was in which group.

VO2 max

Training increases athletes’ maximal oxygen uptake capacity – the VO2 max. ‘However, we saw a larger VO2 max increase in the protein group’, Knuiman says. ‘The additional protein intake also had an effect on their body composition: the amount of lean body mass increased in the protein group, while their fat mass decreased. ‘Such an improved body composition is favourable for both health and sports performance’, Knuiman says. Although the VO2 max is an important determining factor for performance, Knuiman cannot conclude that protein drinks also increase performance solely based on his research. ‘Our study was focused on the VO2 max as result measure. To be able to demonstrate a statistically significant difference in performance capacity, we would need more test subjects.’


Besides the oxygen uptake capacity, Knuiman also investigated changes in the muscle tissue. ‘Training improves the oxidative capacity of a muscle: it acquires a higher capacity to generate adenosine triphosphate molecules (ATP) using oxygen. We measured this oxidative capacity based on the maximum enzyme activity. Muscles contains all kinds of enzymes, and the activity of these enzymes largely determines the oxidative capacity of the muscles.’ Knuiman did not find a significantly greater increase in enzyme activity in the men who consumed the protein drinks. But he did see a trend towards higher activity, which would suggest that their muscles had gone through bigger changes as a result of the training and were therefore better able to perform this type of intensive training.

The effects of additional protein that Knuiman found are therefore positive. Does that mean he will be advising all endurance athletes to ingest additional proteins? ‘Not just yet. It seems to have been an effective strategy with our training programme. However, future research will have to show whether it also has an effect with different training frequencies, training intensity and training status of the individual.’

Pim Knuiman will be defending his thesis Nutritional impact on molecular and physiological adaptations to exercise – nutrition matters on 11 October 2019.

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