Fatigue is natural. The body gets tired and sore after physical activity. There is mental fatigue as well, but in fitness, the term usually refers to a more intense feeling of tiredness. When experienced physically, fatigue can lead to throbbing and quivering muscles, inhibited movement, queasiness and even lightheadedness. None of this sounds fun, but what if there was a way to use this feeling in a measured way to get fitter and build endurance thereby pushing the body’s fatigue threshold even further?

The first time I heard of “training in fatigue” was during an interview with Peter Hartley, former captain of Jamshedpur FC, for a Lounge story titled ISL: How Jamshedpur FC’s Peter Hartley trains to win. In the interview, Hartley revealed that he liked to do a light leg workout the day after a match. Casual fitness enthusiasts might find it hard to imagine doing a leg workout after a football game played at the highest professional level in the country, but Hartley is following what has now become a well-established science of working out.

But it’s important to know how far to take fatigue. There are two kinds: peripheral and central. These, along with muscle damage (the healthy kind that rebuilds itself stronger and larger with the right nutrition and care) make up what we broadly experience as fatigue.

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“Within a training session and throughout a training week, there is a minimum amount of ‘effective reps’ or ‘effective training’ that needs to be done to stimulate adaptation. That means a certain amount of peripheral fatigue is required within each session for it to be maximally effective. Does that mean we should take every set to muscular failure? Well, it’s not that simple. Theoretically, yes, that would maximise the number of effective reps, but there is a cost to taking things too far,” says an article titled The Mechanisms of Training Fatigue on beyondbodybuilding.com.

Advanced bodybuilders use metrics such as maintenance volume, minimum effective volume, maximum adaptive volume and maximum recoverable volume to design their training plans. For those at the intermediate level, however, finding the sweet spot of fatigue usually comes with experience. For beginners, the goal should be simpler: push through a little fatigue regularly to keep progressing. What does that look like? Do a couple of extra reps closer to failure if you still have them in the tank. Challenge the 15-rep mandate if you can. While running, go the extra 20 metres. Over time, this healthy way of pushing past barriers can help build endurance, strength and stimulate growth.

One thing you might notice when the body is fatigued is decreased flexibility and eccentric strength. Take, for example, how both can diminish after high-volume or heavy bicep curls. This is where you need to be smart about how far to take a set or push past fatigue. There is little point in continuing an exercise when the body is completely refusing to budge.

There are other advantages to using fatigue smartly as you advance in your fitness journey. One that caught my eye was mentioned in a study titled Injury Prevention Training in Football: Time to Consider Training under Fatigue? According to the paper, balance work and certain injury-prevention exercises may actually be more effective when performed under fatigue rather than when the body is fresh.

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“In terms of injury prevention training, the general approach is to perform drills earlier in the session, often in a non-fatigued state. The justification is that players perform efforts in a ‘fresh condition’ that allows the musculature to produce appropriate protective responses in maintaining stability, balance and body control. We propose some injury prevention training would be effective when performed after rather than before fatigue sets in. The reality of a match is that players execute specific tasks in both non-fatigued and fatigued conditions. Hence, training in both conditions might benefit players,” the study notes.

Some pre-habilitative exercises done after a workout can be a good starting point for those who want to use the body’s fatigued state to improve. For instance, you could do glute bridges or knee-strengthening exercises after a leg day, floor angels after a back workout, or even a short balance routine after any session that challenges stability. There are plenty of combinations to try.

Another example comes from trainer Darcy Norman in an Outside piece titled Training When You’re Tired Will Make You a Better Athlete. “Bricks are workouts in which you perform one type of movement, like biking, and then immediately switch to another that uses complementary muscles, like running, which forces your body to adapt quickly,” says Norman, who has worked with top European clubs AS Roma and Bayern Munich. Fatigue, when combined with smart workout design, recovery and nutrition, can push the body to adapt, repair and grow in ways that improve multiple facets of physical training.

Pulasta Dhar is a football commentator and writer.

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