Ice hockey is one of the world’s toughest sports, and being competitive requires high intensity and a strong physique. New research shows that the ability to perform high-intensity activities especially distinguishes the best from the next best players and young from older players. The ability to sprint declines with age, so older players have to compensate in other ways. More surprisingly, the research also shows that the repeated short bursts of power in ice hockey deplete carbohydrate reserves just as much as more endurance-oriented sports such as football. The new knowledge can strongly influence the diet and training of elite athletes.
To the untrained eye, ice hockey players seem to have barely stepped onto the ice before jumping over the railings again onto the players’ bench. A few sprints, a few body checks and at best a few shots. So what does it really take to get to the pinnacle of ice hockey? Researchers from Aarhus University and the University of Southern Denmark are attempting to answer this question, and they have now come much closer through several studies of elite ice hockey players during training and games.
“The ability to perform high-intensity activities constitutes the primary difference between young and older players and between levels of play. Interestingly, when we examine energy metabolism during games we find that the carbohydrate stores of the muscles are more severely taxed than previously believed. Training and diet in connection with games may therefore need to be reconsidered,” explains main author Jeppe F. Vigh-Larsen, PhD student, Department of Public Health, Aarhus University.
Carbohydrate is depleted in individual muscle fibres during games
The new studies had a practical focus: testing the athletes to optimize performance, recovery and diet. They also had a theoretical focus: understanding what happens in the body at the cellular level during high-intensity intermittent exercise. The researchers therefore collaborated with Denmark’s under-20 national ice hockey team to measure the physical demands during games.
“Although the players are only on the ice in short bursts of 30–60 seconds before they are benched again, the vast majority of the work is at high intensity and is facilitated by close interaction between aerobic and anaerobic energy systems. So perhaps the short work periods are a prerequisite enabling the players to perform maximally when on the ice, which is reflected in high individual muscle lactate concentrations and acute declines in muscle energy reserves when measured immediately after coming off the ice,” says Jeppe F. Vigh-Larsen.
To create as accurate a snapshot as possible, the researchers took muscle samples just 30–45 seconds after the players left the ice. The picture this presented of how the players mobilized energy was rather surprising. High-intensity muscle work considerably increases the metabolism of muscle glycogen, but the depletion of glycogen reserves has not usually been recognized as a major factor in ice hockey because of the relatively short total working time.
“We confirmed the great anaerobic contribution to energy metabolism, but the breakdown of muscle glycogen was much higher than expected and similar to that of football players, even though ice hockey players are only active for about 20 minutes in a game. Of course, the individual differences are large, but for the players exposed to the most playing time, a decline in glycogen seems to be an important factor at the end of games,” explains Jeppe F. Vigh-Larsen.
The total decline in muscle glycogen during the games exceeded 50%, but more interesting was that the distribution of glycogen in the individual muscle fibres differed greatly. Some fibres were still half full after a game, while others were completely empty, and this can potentially be a problem during high-intensity activities requiring the recruitment of all muscle fibres, if some do not have the energy reserves to contribute optimally.
“Other recent results show that glycogen reserves are located in different parts of a muscle cell with possible peculiar effects on the muscles’ ability to function optimally. Our future research will therefore focus on trying to understand these differences and whether specific reserves are depleted more rapidly than others during high-intensity work such as ice hockey and how this affects the ability to perform maximum work,” says Jeppe F. Vigh-Larsen.
High-intensity work capacity on the ice separates the best from the next best
The new results thus emphasize that ice hockey is a very high-intensity sport that places diverse demands on the players’ physique, including explosive acceleration, strength and endurance. A decline in muscle glycogen may affect the ability to sustain high-intensity activity at the end of games and perhaps especially during tournament periods, with many games within a short time-span.
So what are the physical characteristics of elite ice hockey players? The researchers investigated this by testing almost 200 top ice hockey players in both Denmark and Finland, including several world champions.
“They were tested off the ice, where we analysed weight, height, body mass and explosive muscle strength through jumping height, and then we did several tests on the ice, including a 30-metre sprint test and a variant of the classic beep test to determine aerobic capacity,” explains Jeppe F. Vigh-Larsen.
The main finding was that the elite players in Finland had a higher level than those in Denmark, as measured by their ability to perform single and repeated high-intensity activity on the ice. For example, the difference in sprint ability was up to 5%, and the difference in the beep test was almost 15%. Conversely, they did not differ in explosive muscle strength off the ice nor in body composition.
“This is an interesting finding. Even at the elite level, players from different leagues differ in physical ability, and the single and repeated high-intensity activities on the ice especially distinguishes between levels of play. This can affect how players should train, and we are currently analysing the results from a training study conducted in collaboration with researchers from the University of Copenhagen suggesting that very intense training on the ice – speed endurance exercise – can be key to improving this,” says Jeppe F. Vigh-Larsen.
Older players are less explosive but have more muscle mass
Similarly, the differences between young and older players were analysed, and the main difference was a decrease in single high-intensity work ability of up to 5% for the players older than 30 years. On the other hand, the youngest players 18–21 years old had 7% less muscle mass, whereas no differences were present in aerobic capacity between age groups.
“These differences may seem small, but remember that these are elite players, and even minor differences can have great significance. So the oldest players primarily seem challenged in sprinting abilities but have a little more mass and strength and then they probably benefit from greater experience,” explains Jeppe F. Vigh-Larsen.
The ice hockey project is part of Denmark’s Network for Performance, Recovery and Diet Optimization in Intermittent Sports (PRoKIT) under the auspices of Team Denmark, which aims to map performance, recovery and diet optimization for elite athletes in intermittent sports such as handball, football, ice hockey and badminton. The goal is to get even closer to achieving top performance in the most important competitions, and the new studies can contribute to this.
“The study of the elite hockey players in Finland and Denmark and the analysis of the age-specific differences indicate where further training is needed in various contexts, and the study of energy metabolism during games provides important knowledge about the importance of carbohydrate for this type of performance and inspiration for future intervention studies. We used to think that the time of muscle work was too short for carbohydrate reserves to be depleted, but since many individual fibres are depleted, optimizing strategies for energy intake before, during and after games makes eminent sense,” concludes Jeppe F. Vigh-Larsen.