Recovery nutrition: starting on the move!

Percentage figures shown for each line represent the % of sustainable intensity. As the percentage of maximum sustainable intensity rises, the time taken to deplete glycogen stores diminishes. At 64% maximum, glycogen levels have dropped to 20mmol/kg after 105 minutes. At 83% of maximum, this takes just 60 minutes, while at 120% of maximum, it takes a mere 20 minutes.

*Adapted from Jeukendrup and Gleeson 2004; Sport Nutrition: ‘An introduction to energy production and performance’.

As a result, we now know that the highest muscle glycogen synthesis rates occur when relatively large amounts of carbohydrate (1 – 1.5 grams per kilo of bodyweight per hour) are consumed immediately after exercise, and then at 30–60 minute intervals thereafter, for up to five hours (depending on the duration of the prior exercise)(6). For a 70kg athlete for example, this would mean consuming 70 to 115g of carbohydrate immediately after exercise and then repeating at regular intervals. After a hard 1-hour run, repeating this dose just once would probably suffice. After a hard 3-hour run, he/she might need to repeat this dose hourly for 5 hours.

Post exercise recovery strategies

The best strategies for post-exercise carbohydrate feeding and the optimum day-to-day carbohydrate-rich diet that best supports post-exercise recovery is a topic that we have covered on many occasions in previous SPB articles. In particular, readers will find the following articles particularly informative:

·        Carbohydrate - still your best performance friend!

·        Overtraining: how the right nutrition can help prevent it and keep you on top form!

·        Post-exercise carbohydrate for recovery: fast or slow?

·        Food vs. sports drinks: what’s really better for recovery?

What’s well accepted among sports scientists is that to be maximally effective, recovery nutrition - and in particular, carbohydrate feeding - needs to begin as soon as possible following a bout of exercise. As SPB contributor Nick Broad explains in an earlier SPB article, the drive to consume carbohydrate as early as possible after activity derives from the early work of Professor Louise Burke, head of the Australian Institute of Sport’s nutrition department^(7,8), and John Ivy in Texas^(9,10), whose primary concern (and this is the important point) was to maximise the rate of muscle glycogen synthesis after exercise. They were hell bent on recovering muscle glycogen as fast as possible so that performance in an event or training session occurring up to 24 hours later did not suffer.

Recovery during exercise?

We know that starting recovery nutrition as soon as possible following exercise is critical for maximising the speed and extent of recovery. So here’s a question: could there be a benefit from starting recovery with carbohydrate feeding even earlier – ie during exercise? In other words, does feeding carbohydrate during a prior bout of exercise help stem the depletion of muscle glycogen during that exercise bout, thereby improving performance in a next day bout of exercise? Well, that is precisely the question a team of Norwegian researchers have asked in a brand new study just published in the journal Medicine and Science in Sports and Exercise⁽¹¹⁾.

In this study, researchers investigated the effect of carbohydrate ingestion during standardized exercise with and without exhaustion on protein degradation (ie muscle breakdown) and next-day performance in male cyclists. Seven highly trained cyclists performed two cycling trials on two separate occasions separated by seven days. In both trials, the cyclists were asked to pedal to exhaustion by riding firstly for 2.5 hours at a power output required around 68% of their maximum oxygen uptake (VO2max), which subjectively equates to a moderate to slightly hard tempo. Following the steady-state task, they then repeated a series of 1-minute work intervals at 90% of VO2max (hard!) separated by 60-second recoveries until they reached the point of exhaustion. The two trials were identical except for what the cyclists drank during the steady-state work:

·        A carbohydrate drink providing around 1 gram of carbohydrate per kilo of bodyweight per hour.

·        An identical tasting drink containing zero carbohydrate (the placebo condition).

The cyclists’ diets were also standardized to ensure their carbohydrate intake was the same in the days before each trial.

The day after both trials (ie within 24 hours), the cyclists had to complete a 20km time trial in order to test the impact of consuming ‘during-exercise’ carbohydrate on their recovery ability. In addition, the cyclists were assessed for their cycling efficiency - also known as ‘economy’ - a measure of how efficiently chemical energy in the muscles is converted into locomotion. High levels of economy (muscle efficiency) in endurance athletes are known to be critical for superior endurance performance^(12-14). Finally, blood levels of tyrosine and phenylalanine were also measured post-time trial to assess the degree of muscle tissue breakdown and metabolic stress the time trial induced.

What they found

There were a number of findings, suggesting a distinct advantage to consuming ‘in-exercise’ carbohydrate:

·        Next-day performance during the time trial was significantly better when carbohydrate was ingested the day before, with any average time of 41mins 49secs for the time trial compared to an average time of 42mins50 secs when the no-carbohydrate drink was taken the day before (see figure 2).

·        Cycling efficiency was higher in the time trial when carbohydrate was consumed in the previous day’s exercise bout (18.6% in carbohydrate vs. 17.9% placebo).

·        Tyrosine and phenylalanine plasma concentrations significantly increased when the placebo drink had been consumed the day before but remained similar when carbohydrate had been consumed (indicating less muscle breakdown and reduced metabolic stress).

The researchers concluded by stating that ‘carbohydrate ingestion during exhaustive exercise reduced deterioration in next-day performance through reduced metabolic stress and development of fatigue, and also indicated less muscle protein degradation, which helps preserve muscle function.

Figure 2: Time trial times with and without prior-day in-exercise carbohydrate feeding

Practical implications for athletes

When fast recovery for next day performance is essential – for example, when competing in a multiday event – these findings demonstrate that in-exercise carbohydrate feeding is a useful strategy. This is particularly the case when athletes are undertaking a long and/or exhausting bout of exercise, where post-exercise carbohydrate feeding is unable to restore the lost muscle glycogen within the next 24 hours or so.

The reason why in-exercise feeding can help next-day performance is simple; by supplying the working muscles with an ingested source of carbohydrate during exercise, muscle stores of glycogen are spared, which means there’s less ‘topping up’ required to fully replenish glycogen levels. This is turn means that glycogen replenishment can be achieved sooner.

In-exercise carbohydrate feeding is not always good!

At this point, you might be wondering if consuming carbohydrate during ALL exercise bouts is a good strategy? The answer is an emphatic no, and the reason is related to training responses and adaptation. In simple terms, if muscles are always trained with ample carbohydrate to draw on, fat adaptation may not be maximized. In other words, the muscles will not become as efficient at fat burning as they could be because they’re not frequently trained in a carbohydrate-depleted state⁽¹⁵⁾. Although not an issue for shorter-duration events, sub-optimal fat adaptation does matter for longer events such as the marathon because at these distances, glycogen depletion can become a real problem, which means good fat burning becomes essential⁽¹⁶⁾.

Another reason for not always consuming carbohydrate drinks in every training session is to do with training adaptation. When muscle glycogen stores become somewhat depleted (ie when carbs are NOT consumed during a long training session), a muscle enzyme called ‘AMP-activated protein kinase’ becomes activated, which in turn stimulates a key signalling molecule called PGC-1α^(17,18).

Increased PGC-1α activity is associated with mitochondrial synthesis – ie switches on genes that manufacture new mitochondria⁽¹⁹⁾. That matters because mitochondria are the aerobic energy factories in cells; the more mitochondria per unit volume of muscle, the greater the aerobic energy producing capacity - a key hallmark of endurance training adaptation (increased aerobic fitness)⁽²⁰⁾. With the above in mind, we can summarize as follows:

·        If your goal is to recover as fast as possible for an event or important training session the next day, you should consume carbohydrate during today’s exercise bout/competition at the rate of around 1 gram per hour per kilo of your bodyweight. You should then follow up with carbohydrate-rich foods for the rest of the day and for breakfast the next morning.

·        The same is true if you are participating in a multiday endurance event.

·        If your goal is to maximize your fat burning capacity to extend endurance for a long event such as a marathon, you should complete at least 90 minutes of your training session without consuming carbohydrate, and only then switch to carbohydrate consumption. The same is true for athletes whose primary goal is weight loss.

·        If you are training infrequently (twice per week or less), there’s no need to use in-exercise carbohydrate unless you need it to help complete long workouts. There’s also no need to consume a particularly carbohydrate-rich diet in between workout as there’s ample time for muscle glycogen re-synthesis!

References

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