Imagine that you, the athlete, have two fuel tanks, filled with resources that each of the performance subsystems (neural, muscular, metabolic, and mental subsystems) requires to function. The first fuel tank is the fitness tank, which has the capacity to support your normal level of exercise and daily activities – this tank’s capacity is expanded through training. The second fuel tank is the body’s deeper survival reserve which, biologically, is meant to be tapped into only for serious emergencies.
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The first tank is constantly replenished by the body, but at a rate that takes a whole day to refill when the balance of exercise and rest is set to what the body is currently adapted to (the type and level of activity that has been normalized). This constant rate of replenishment is why a few seconds rest between repeats can allow you to resume the activity, but you can only do that a number of times before fatigue is too great and then you need to switch to another activity that loads a different subsystem or stop the practice for the day.
The second reserve tank, if tapped, is replenished slowly, taking days and the deeper it is tapped, the longer it takes. The body taps into this reserve tank when it is pushed to perform beyond what the first fitness tank can support – when the activity is too intense or going too long, or if the level of stressful activity stays too high day after day, week after week. The more that this second tank is depleted, the more slowly the first tank is replenished also. If your body has been tapping into the second reserve tank you will notice that a normal night’s rest is not enough for your first tank to feel replenished.
A well-tuned individualized training plan will have you use up the first fuel tank each day, and over the week, just barely tap into the second tank. Over a few weeks, that tapping of the second tank will lead to a slight accumulated deficit. That deficit can be experienced as both a physical and mental reduction in energy and motivation. If you are dipping too far into the second fuel tank, or dipping a little but for too long without allowing it to replenish resources, the body will protest and start resisting activity in some way or another – attitude, injury, or illness (physical or mental) being the most obvious forms. If there is a deficit after a few weeks, you need to not just replenish the first tank but calm things way down in your training (and possibly in your life) and let that second reserve tank replenish, let physical and mental healing occur.
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The analogy of the two fuel tanks is a helpful way to understand the body’s energy systems.
Hey Michelle, I am glad you found the analogy helpful. My intention is that we can better sense that optimal spot between too little and too much fatigue and know when its time to rejuvenate.
Hi Mat, when exercising in the pool, should we increase our nonstop swimming distance gradually and then rest (endurance) or should we rest in intervals and increase the pace while not let the number of strokes increase at the same distance?
Hi Selin. Thanks for inquiring. Both are valid ways of approaching this, but it depends on what stage of development you are in for the season or for your event. If you are starting a new season or newer to swimming and need to build up basic strength, then gradually increasing distance (up to event like distance, if that is practical), at moderate or low intensity, is recommended. Once you feel strong just swimming the full distance at low and moderate intensity, then you enter a new stage of building strength within that full distance. Break up the full distance into smaller intervals and increase the intensity per interval with rest between, so that your body is now challenged to do the same distance but under higher loading.