Every summer, footballers return for pre-season and complain about how hard the first weeks feel. By the opening match, the same sessions feel much easier. The players have not found a secret. They have experienced overload, the most basic principle in fitness training.
So, how does overload affect fitness training? In short, it is the reason training works at all, but too much of it causes injury and burnout. This article explains what the overload principle means, how the body adapts, how football clubs measure it, and why players’ unions now see overload as one of the game’s biggest problems.
What Is the Overload Principle?
The overload principle says the body only improves when it is asked to do more than it is used to. If you always run the same distance at the same speed, your body has no reason to change. Add more distance, more speed or more weight, and it is forced to adapt.
The idea is often explained with the ancient Greek legend of Milo of Croton, a wrestler said to have carried a young calf on his shoulders every day. As the calf grew into a bull, Milo’s strength grew with it. The story is a myth, but it describes progressive overload well: small, regular increases over a long period.
How Overload Makes You Fitter
A hard session creates temporary fatigue and small amounts of stress in muscles, tendons and the heart and lungs. During rest, the body repairs itself and becomes slightly stronger than before, so it can cope better next time. Sports scientists call this cycle stress, recovery and adaptation. Without the recovery part, there is no adaptation, only more fatigue.
You can apply overload in several ways: train more often, train harder, train for longer, or change the type of exercise. Coaches usually change one of these factors at a time, which makes it easier to see what is working and to avoid doing too much too soon.
How Football Clubs Manage Overload
Professional clubs no longer guess how hard players are working. GPS vests, heart-rate monitors and player questionnaires record distance covered, high-speed running and how tired players feel. Coaches also adjust drills: smaller pitches and fewer players in small-sided games usually increase intensity, while larger spaces add more running.
One of the most influential ideas in this area comes from Australian sports scientist Tim Gabbett. In a 2016 paper in the British Journal of Sports Medicine, he compared a player’s training load from the last week (acute load) with their average over the previous four weeks (chronic load). This is known as the acute:chronic workload ratio.
Gabbett suggested that a ratio between 0.8 and 1.3 was a training sweet spot with lower injury risk, while a ratio of 1.5 or higher was a danger zone. He also described the training-injury prevention paradox: players who build high workloads gradually become more resistant to injury. Later studies have questioned whether the exact sweet spot applies to everyone, but the main message is widely accepted. Sudden spikes in workload are risky.
When Overload Goes Too Far
Overreaching and Overtraining
Experts separate normal hard training from harmful overload. Short periods of very heavy training that cause a temporary drop in performance, followed by improvement after rest, are called functional overreaching. If performance stays low for weeks, it becomes non-functional overreaching. The most serious stage, overtraining syndrome, can affect performance, mood and sleep for months.
Warning signs include constant tiredness, poor sleep, heavy legs, falling performance and losing motivation. For recreational players, the answer is usually simple: take extra rest days and reduce the load before increasing it again.
The Fixture Congestion Debate
At the elite level, overload is now a major political issue. The global players’ union FIFPRO defines back-to-back matches as games separated by less than five days. Its high-performance experts recommend that players receive at least 28 days off in the off-season and a 14-day break during the season.
Reality often looks very different. FIFPRO’s 2025 workload report found that only 14% of sampled players from Euro 2024 had the recommended 28 days of off-season rest before the following season. For Copa América players based in Europe’s top five leagues, the figure was just 9%.
Using Overload the Right Way
The overload principle works for everyone, from Champions League players to Sunday league teams. Increase the challenge gradually, change one factor at a time, and plan rest as carefully as training. Fitness improves during recovery, not during the session itself. Get that balance right and overload becomes the reason you improve, not the reason you end up injured.
