Use it or Lose it: Finding the Sweet-spot for the Off-season
All athletes take them, and all coaches should programme them: lay-offs. This may be a relative term since the degree of ‘laying off‘ required will depend on the accumulated training load of the preceding season, amidst life’s various obstacles. Regardless, recovery is increasingly being perceived as important as training itself for achieving fitness and performance goals. Pre- or in-season this may entail a rest day here and there, or an ‘active recovery’ day. During the off-season, however, athletes may take days, weeks or even months away from training to afford the body and mind time to recover, revitalise and return ready to train intensely for another season. But how much ‘off-time’ is too much? Is it possible to lose those hard-earned adaptations? The answers may be quite disconcerting, but there are means to taking some time off, yet returning without huffing and puffing after the warm up.
Consistent training plays a critical role in advancing athletic performance through various physiological adaptations. However, these are transitory and reversible, and insufficient training stimulus will induce a partial or complete loss of adaptations (‘de-training’), the extent of which depends on how training load is altered i.e. reduced or stopped. Regardless, detraining occurs fairly rapidly and 8 weeks without training has been found to induce a pronounced deterioration of training-induced adaptations, even in elite athletes. Interestingly, studies have shown that different training-induced adaptations decay at different rates3. Coyle et al. (1984) showed years ago that maximal oxygen uptake (VO2max) begins to decline within the first week of detraining (Figure 1). VO2max represents the upper limit of the cardiorespiratory system and is altered either by changes in cardiac output or the arteriovenous difference in oxygen. The latter reflects how much oxygen can be extracted from the blood as it passes through the body. The initial decline in VO2max is accounted for by reduced cardiac output since blood volume and stroke volume are significantly reduced, and the increase in heart rate offers inadequate compensation (Figure 1). The slow decline in VO2max thereafter, which remains above both pre-training and sedentary control levels, results from the reduced arteriovenous difference in oxygen[3,4]. This is caused primarily by reduced haemoglobin mass and hence oxygen-carrying capacity, as well as reduced mitochondrial density and early reductions in the presence of skeletal muscle oxidative enzymes. The drop in VO2max can thus be seen in two parts: an initial loss of central adaptations followed by reduced peripheral capacity at the specific muscles.
The ability to sustain a high fraction of VO2max for a given duration, known as ‘aerobic endurance’, also follows a rapid decline within 2-3 weeks without training. Aerobic endurance improves concomitantly with oxidative enzyme capacity as athletes require rapid oxidative energy production to sustain high-intensity activities. The ‘de-training’ of (carbohydrate and fat) oxidative enzymes impairs oxidative energy production and places increased reliance on glycolytic energy production[4,5]. Furthermore, reduced expression of both Glycogen Synthase within 5 days and Glucose Transporter 4 within 1-2 weeks (facilitate glycogen synthesis and oxygen uptake into the muscle, respectively), together cause a rapid decline in muscle glycogen storage capacity – up to 20% within one week. Collectively, these impair the capacity to sustain high-intensity activity, as evidenced by the rapid increase of both RER and blood lactate at a given intensity, concomitant with a progressive decline in lactate threshold and overall performance.
Despite the declines in VO2max and aerobic endurance, ‘energy efficiency’ or the energy cost at a given submaximal intensity is largely maintained, even after 84 days of training cessation. This may be explained by the significant contribution of neuromuscular factors to movement efficiency, including muscle strength and power and the capacity to store and recoil elastic energy. These traits are more robust to training cessation and undergo insignificant declines during the first 3 weeks of inactivity. Hence, strength and power or sprint athletes typically find it easier than endurance athletes to return to action after a lay-off. Importantly, although the energy demand is the same, the strategy adopted by the athlete to meet this demand has had to change. Given the reduced VO2max, the workload is at a higher relative intensity, both perceived effort and RER are higher, glycogen is being utilised more rapidly and oxidative capacity is reduced. Effectively, the time the athlete will be able to sustain that intensity will be significantly reduced.
In light of this, how should plan a detraining phase or return a ‘de-trained’ athlete to regular training? Clearly detraining occurs rapidly and it is important (if possible) to counteract the decay of previously acquired adaptations. In doing so one needs to consider the time-course of detraining: central adaptations followed by peripheral, and most recent followed by long-standing. Since cardiorespiratory fitness is not specific to the working muscles, one may integrate alternative exercise modalities to keep the cardiorespiratory system stimulated.
However, given the metabolic consequences in the trained muscles, sports that utilise the same muscle groups should at least be performed to retain these adaptations. Performing dissimilar activities alone (e.g. swimming for runners) may maintain VO2max, but aerobic endurance will deteriorate. In most cases, it will be better to reduce rather than cease performance of the athlete’s primary activity; specifically: reducing frequency moderately and volume markedly, but maintaining intensity, appears most effective at retaining both VO2max and aerobic endurance[1,5]. In fact, if this ‘reduction’ phase lasts 2 weeks, it begins to resemble a ‘taper’ and may facilitate improved readiness to train. Fortunately for resistance-trained athletes, strength adaptations decay slower than aerobic adaptations, reducing by 6 to 9% after 4 weeks. However, similar to endurance athletes, reducing volume but maintaining intensity is more effective at retaining or even marginally improving strength measures.
What of those (normally more recreational) athletes who have afforded themselves an extended break from activity? Fortunately ‘residual fitness’ is there to help! Prior neural connections will help to relearn the requisite coordination, and psychologically returning to an activity they previously enjoyed will make retraining easier. Recent evidence has also given credence to the notion of ‘muscle memory’, whereby training adaptations are ‘remembered’ by the muscle in DNA-containing nuclei (myonuclei) that will proliferate and restore adaptations when stimulated again. In other words, years of prior training will largely influence the retention of adaptations and ability to retrain. This means that for endurance athletes, endurance adaptations will be more easily restored than those accrued from high-intensity interval training, since the latter has likely formed a lesser part of their total training history. Therefore, be careful to increase training load variables progressively and in accordance with objective and subjective athlete feedback. It may not always be “just like riding a bicycle”!
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