Being tired is not proof you trained

A session disturbs your muscles. Fuel runs down, the chemistry inside each fibre shifts, and some fibres are strained. That disturbance is the signal to build. The signal is short. The building it starts is slow, and it runs on for a day or two after you stop.

When researchers measured thigh muscle after a single session with weights, the muscle was still building protein two days later. The same pattern, a short signal and slow building after it, holds for the mitochondria, the power plants in your muscles, and for your tendons.

The fitness a session makes is small and lasts for weeks. The fatigue is large and clears within days. On any morning, how fast you swim is roughly the fitness you have built minus the fatigue you still carry. That is why the pace clock read three seconds slower than on Monday, and why the gain from a session shows only once its tiredness has gone.

So the tiredness after the repeats tells you how much fatigue the session made. It does not tell you how much signal it sent. The grey zone, the effort halfway between base and threshold, costs you fatigue and sends only a weak signal.

Researchers took 33 trained male triathletes through eight weeks of training. Ten of them trained as normal throughout. The other 23 made every session about a third longer for three weeks, at the same effort. Then everyone cut back for four weeks, a taper, the way athletes do before a race.

By the end of the three long weeks, the 23 who trained more had split into two groups. Twelve were tired, but their cycling test held. They were absorbing the extra work. Eleven had sunk further. They felt worn out, and their test had got worse. Sports scientists call that deeper state overreaching. Stay in it for months, and it becomes overtraining.

The taper showed which group had gained. The twelve who absorbed the extra work improved their cycling test by about 2.6 percent more than the ten who trained as normal. The eleven who sank ended no better than those ten, as if they had never done the extra weeks. The most oxygen their bodies could use did not rise.

So the lesson is not to train less. The twelve and the eleven did exactly the same extra training. One group absorbed it, and the other sank into it. The researchers concluded that extra training before a taper helps, "but not in the presence of" overreaching.

What you can absorb is not set by training alone. The European College of Sport Science and the American College of Sports Medicine describe overtraining as "the sum of multiple life stressors", and they count sleep loss among them. A night broken by a baby and a week of deadlines draw on the same reserve as the training.

Fatigue you are absorbing comes from the last session. Your legs are heavy that evening, lighter the next morning, and fine a day or two later. You sleep deeply, and you want to train again.

Fatigue you are sinking into is carried over from many sessions, and from the rest of your life. Your legs stay heavy from one day to the next. You sleep less, and lightly. Your mood goes flat, and you snap at the people you live with. Base efforts feel harder than they should.

How wrecked you feel straight after a session tells you what it cost. The next morning tells you whether you absorbed it.

Legs, sleep and mood need nothing but your attention. If you also take a resting heart reading each morning, read it as a trend over a week, and trust it in one direction only. A reading that worsens is a warning. A good one proves nothing, because the reading shows only how hard the nerves that slow your heart are working, and deep fatigue can make them work harder too. In triathletes who had trained into deep fatigue, the morning readings looked better while their running got worse. Heart rate is a guide, not a measuring stick.

Take the next few days at base, or rest, and make sure base really is base. It should feel like almost nothing: you breathe through your nose, you could talk in full sentences, and it rates about a 3 out of 10. If it feels like more, slow down, and walk the hills if you have to. A base session should leave you feeling better than when you started, never tired. Sleep as much as your life allows. Come back to threshold or VO₂max when the mornings feel good again.

Researchers followed elite Australian track and field athletes for five seasons. The athletes who completed the most training weeks were the ones most likely to reach their goal at the championships.

You string the weeks together only when each is a week you can absorb and then do again.

Three mornings of VO₂max after broken nights feel like dedication. One or two, on mornings you wake up fresh, are what you can still be doing in six months. It is the months of those weeks, not any one morning, that make you fit.