With cup after cup added to the international circuit, a professional footballer’s schedule is more physically demanding than ever. New research published last August in Medicine & Science in Sports & Exercise suggests that extra time – the 30 minutes tacked on to the end of regulation time if the score is tied – has an outsized impact, depleting important stores of energy in players’ muscles and worsening performance metrics such as pass completions.
With cup after cup added to the international circuit, a professional footballer’s schedule is more physically demanding than ever. New research published last August in Medicine & Science in Sports & Exercise suggests that extra time – the 30 minutes tacked on to the end of regulation time if the score is tied – has an outsized impact, depleting important stores of energy in players’ muscles and worsening performance metrics such as pass completions.
An intensive study sponsored by the Union of European Football Associations (UEFA) used precise GPS tracking, heart-rate monitors, blood analysis and even muscle samples taken during test matches to see how extra time affects players’ bodies.
“This is something the players are concerned about – especially high-profile players, who are playing the most,” says Magni Mohr, the study’s lead author and a biomechanics professor at the University of Southern Denmark who studies fatigue in elite athletes.
A punishing schedule
Comparing the workload of today’s professional footballers to decades past, “the time spent on training and games has exploded,” Mohr explains. “There is much more match play and games at a much higher intensity.”
As if that were not enough, the percentage of games that are not settled within regulation time is also rising – a change Mohr puts down to more competitive matches. “If we look at the recent international tournaments, 40–50% of games in the knockout stages have gone into extra time,” he says. And in 2021, UEFA decided to end the away goals rule, which had been used since 1965 to determine which teams advance out of knockout rounds in the event of a tie by weighting goals scored at an opponent’s stadium higher than goals scored at home. Without the away goals rule, even more games will go into extra time.
The cumulative effects of all this extra time could well be decisive in matches. “Consider this as an additional load in something that is already close to exploding,” Mohr says.
An odyssey of tests
To track how a single match with added extra time affects footballers’ bodies, Mohr and his team recruited 20 semiprofessional football players for a multidimensional study in Greece.
The researchers tested the players’ body condition and performance at three stages: before the game, to establish a baseline; after the 90 minutes of regular play; and after 30 minutes of extra time.
At each checkpoint, the players performed a series of sprints to assess their endurance and level of fatigue, lifted weights by extending and flexing their knees and completed jump trials to test the explosive power of their lower bodies. The scientists also drew blood and took samples from the quadriceps muscles on the athletes’ dominant legs to measure their energy stores.
“In muscle cells we have depots of glycogen, which are long chains of glucose molecules,” Mohr explains. “When we exercise, we use some of this muscle glycogen to provide energy to the cells.” Previous laboratory work has shown that these glycogen stores do not have to be totally depleted to affect performance. “When you lose glycogen down to a certain threshold, you have difficulty maintaining the capacity of the processes in the muscles that are generating force,” he says. Could this be why players seem to hit a wall after the 90-minute mark?
What they found
Although it does not take a scientist to realise that longer games are more tiring for players, the results of the study left the researchers “a bit surprised that the impact of the last 30 minutes is as great as it is,” Mohr says.
First, performance changes, and fans can see this. Game-play analysis showed a significant drop in high-intensity running, average speed and ground covered during extra time, with all three measures about 10% lower compared with regulation time. Significantly, the rate of successful passes also fell by 5%. (Spectators in field-level seats or with HD TVs at home might notice that players sweated 25% more during extra time.)
As for the out-of-game performance metrics, players’ jump heights were 19% lower at the 90-minute mark and 27% lower by the end of extra time, and their knee flexor and extensor strength declined by 7–11%. “These are not normally super-sensitive measures of muscle function,” Mohr says, suggesting that the changes observed indicate meaningful shifts in performance.
The blood and tissue samples show changes that might explain what fans see on the pitch. The final blood samples showed a 15% drop in blood glucose after extra time versus constant in the first 90 minutes of play. “This is one of the first studies in football showing signs of low blood glucose values,” Mohr adds.
A comparison of the muscle samples shows that players used up the energy stores in their muscles almost twice as rapidly during extra time. After the regulation 90 minutes of play, the players’ skeletal muscles had depleted about a third of their glycogen. But after extra time, the cellular energy tanks in their muscles were only half full – and the researchers think that this may take them below a key threshold beyond which muscles have more difficulty performing.
Mohr adds that the researchers expected that the players’ bodies would lean harder on an alternative energy source – oxidising fat – to keep the muscles in fighting shape after their long exertion. But the blood samples show only a modest amount of plasma glycerol, a by-product from that process, meaning that the players used fat less than expected.
Extra time, extra rest
Mohr says the results of the study lend credibility to what players, coaches and sports scientists already knew. “The takeaway is that extra time is compromising intensity, that players are fatiguing and that the injury risk could be markedly higher,” he says.
“You need to prepare for this in international football when 120-minute games are possible,” he suggests. “It can be very decisive and can also greatly affect the next game.”
As for recommendations for UEFA and other football organisations looking to protect players from undue fatiguing, “the easiest option is to ensure enough recovery time – add an extra day between matches when they go into extra time,” Mohr says. Years of lobbying by sports researchers – and ultimately pressure from the COVID-19 pandemic – were required for football leagues to increase the number of substitutions from three to five, which has already measurably reduced player fatigue, Mohr adds. But players cannot continue at this breakneck pace without additional support for extra time recovery. “I think that this has to be implemented soon,” he says.