Peak Performance takes a look at some new research on how to potentially maximize interval training results by manipulating the nature of the rest periods in between each effort MORE
Maximising the anabolic response to training
Nick Tiller presents six evidence-driven but seldom practised methods by which athletes can promote the anabolic process to maximise training adaptation, promote recovery and improve athletic performance.
Anabolism is considered to be any state in which nitrogen is retained in lean body mass, and can occur via the stimulation of protein synthesis in the muscle and/or a reduction in the rate of protein breakdown. With respect to exercise training, a state of anabolism is essential if athletes are to optimally experience the muscular adaptations that underpin increases in muscle size, strength and/or endurance.
However, diligent training can often yield less-thanoptimal results and poor conversion to sports performance, if not accompanied by equally conscientious lifestyle choices that complement and positively influence training and recovery.
1. Maximise your sleep – growth hormone and muscle recovery
Your nutrition may be perfect, and your rest-days frequent and effective, but if you’re not obtaining sufficient levels of high-quality sleep, these other factors could be fairly inconsequential; sleep is, without a doubt, the most effective form of recovery we can afford our bodies. It is during our nightly sleep cycle that all non-essential body processes are temporarily relinquished, and our physical resources are devoted to regaining a state of metabolic homeostasis (balance).
The primary mechanism predicating this recovery is the central nervous system’s release of growth hormone (GH) via the hypothalamus (a small cone-shaped structure in the brain that plays a central role in controlling our nervous system). Growth hormone promotes muscle growth and repair by facilitating protein synthesis, attenuating carbohydrate breakdown, and promoting fat burning mechanisms in the body (1).
Although only small, episodic bursts of GH secretion occur during the day, larger concentrations arise in response to exercise and other stresses. However, the most profound daily increase in circulating GH occurs during sleep, at the onset of a deep “stage 3 or 4” sleep usually experienced within three hours after dropping off (2) (see the picture).
During this time, a large, prolonged increase in circulating GH is observed, and it’s quite likely that only sustained GH concentrations of this magnitude are sufficient to exert the GH-mediated effects on tissue growth and remodelling. For optimum recovery, approximately 7.5 hours sleep is recommended for adults, but exercising individuals may require closer to 8 or 9 hours.
Ideally, your sleep should be restful and uninterrupted, and therefore exhibiting high efficiency, i.e. high duration with a low number of “wake bouts” to avoid disrupting the important GH response.
Research also suggests that GH secretion is more sensitive in the early hours of the night, and it would appear that 8 hours sleep between 10pm and 6am is more beneficial than 8 hours between 12am and 8am.
2. Separate your strength and cardio sessions – understand cell signalling
Whether you’re a runner, jumper, thrower or puncher, if you take your sport seriously, your training should be anchored by a comprehensive and sports-specific strength and conditioning programme. This is an essential entity to correct muscle imbalances that predicate injury, build whole-body robustness allowing you to sustain periods of heavy training, and improve sports-specific strength, power or endurance.
Resistance training exerts its beneficial effects through activation of a cell signalling pathways in the body, abstractly referred to as mTORC1, which is responsible for many of the strength and muscle structure adaptations that underpin the response to weight training (3).
In addition to resistance training itself, there are a number of other ways to bring about the activation of mTORC1 and therefore improve strength training adaptations. These include supplementation with amino acids like Leucine, and the release of insulin and insulin-like growth factors (IGF-1) following training.
Conversely, participating in regular “cyclical” cardiovascular exercise like cycling, running, swimming, etc, stimulates improvements in aerobic fitness and endurance through activation of AMPKinase (AMPK), which mediates many of the physiological adaptations thought to be important for successful endurance performance. These include the breakdown of glucose, fatty acid oxidation and mitochondrial biogenesis (4).
However, AMPK has been shown to block the mTORC1 pathway that is largely responsible for the anabolic process, and thus inhibits protein and glycogen synthesis that is essential for the development of muscle mass and recovery.
There is a great deal of research suggesting that concurrent strength and endurance training results are in blunted strength adaptations. This is known as the “Interference Phenomenon” (5). The inhibitory effect of endurance training on the mTORC1 pathway is likely to be responsible.
Although strength and endurance are not necessarily mutually exclusive, in this context they can largely be considered to be the consequence of contradictory adaptive mechanisms.
In a paper published in Sports Medicine in 2000, Docherty and Sporer proposed a model to more comprehensively predict the training protocols that are likely to minimise or maximise the degree of interference. However, in order to maximise improvements in muscle strength resulting from your resistance sessions, it is recommended that you separate your resistance and cardio/endurance training by a minimum of a few hours.
3. Know your protein – presenting facts and dispelling myth
Dietary protein is an important macronutrient, made up of long-chain amino acids, essential for the replacement of both structural and functional proteins that are broken down during training.
Indeed, muscle hypertrophy occurs in the presence of a positive nitrogen balance, and net protein synthesis is a primary mechanism (when synthesis exceeds breakdown) (6).
A deficiency of dietary protein or amino acids has also been associated with an impaired immune function and an increased susceptibility of animals to infectious disease (7). This becomes more pertinent to the exercising individual who may be at further risk of compromised immune function with high stress physical activity, compared to moderate stress (8).
Although the Dietary Reference Intake (DRI) suggests that daily protein ingestion for all individuals aged 19 years and older should be approximately 0.8g protein per kilogram of bodyweight (9), there is a great deal of published literature that suggests those habitually performing heavy strength or endurance exercise require substantially greater protein intake than their sedentary counterparts (10). Further, the more significant the training stress in a given session, the greater the protein turnover will be during and following said session.
Therefore, protein intake of the athletic diet must reflect individual requirements.
Although the best sources of dietary protein come in animal forms (eggs, meat, fish), much of the commercially available protein supplements are whey extracts of some description, which are isolated from whey (a by-product of cheese production). They are usually digested and absorbed into the system fairly quickly, and enter the blood stream within 20-30 minutes.
However, depending on how much you consume in one serving, a large proportion of this protein will be oxidised by the liver before it even reaches the muscle, making much of what you consume an expensive waste!
There certainly exists a dose-response relationship in terms of serving size (i.e. more is better), but only up to a specific threshold, above which no further benefits will be afforded.
A 2009 study by Moore and colleagues (11) provided isolated egg protein to a group of healthy adult males (average bodymass 85kg) following resistance exercise in graded doses from 0g to 40g. The extent of protein synthesis within muscle tissue increased proportionally with the size of the ingested dose up to approximately 20g, but doubling the dose to 40g did not further facilitate the anabolic response.
Due to the fact it’s quickly absorbed, it is recommended you use whey protein during or immediately after training when your muscles need it most. Alternatively, consume your whey protein with sufficient quantities of complex carbohydrates or fat (for example, milk) to slow the rate of absorption, a practice which will yield further benefits to muscle recovery (see carbohydrates below).
For non-training periods, whey protein alone may be insufficient to boost your protein intake, and a source of more slowly absorbed protein in the form of casein may be more effective. Casein has been known to cause gastric problems so experiment with use.
Dietary protein is best sourced from whole foods like lean meat, chicken or turkey, fish, nuts, eggs, or dairy sources, and animal sources of dietary protein are generally preferred as they contain all essential amino acids (those that are not produced naturally in the body) (12). However, when these are not conveniently available, the aforementioned advice on supplements may be beneficial.
4. Manage your calories – promoting positive nitrogen balance and recovery
As previously discussed, consuming adequate quantities of dietary amino acids (from protein) is deemed essential in promoting net protein synthesis within the muscle following training (13).
However, in addition to maintaining relatively high (1.5 to 2 g/kg body weight) protein intake during periods of heavy training, optimising muscle recovery is predicated on maintaining a positive nitrogen balance which is paramount to the anabolic (muscle building) response. This can most effectively be achieved through maintaining dietary protein in addition to a positive calorie intake.
A review study by Lambert and colleagues published in Sports Medicine (14) suggests that for those aiming to increase muscle mass and strength, it is advantageous to maintain a positive energy balance (where energy intake exceeds energy output), and this is deemed necessary to ensure that sufficient energy is available to promote muscle anabolism.
Similarly, a second review article (15) summarised that sustained periods of negative energy balance will lead to the reduction of body mass resulting from a loss of whole-body fat and muscle protein.
It must be remembered that while low-body mass can be useful, and often crucial, in certain weight dependent sports, any athlete existing in a prolonged catabolic state predicated by insufficient energy intake will see reductions in muscle mass and strength which may lead to an increased risk of injury.
Further, failure to maintain a positive nitrogen balance through low energy intake can also lead to compromised immune-function (16). As such, when athletes compete in sports that necessitate more conservative body mass distance running, gymnastics, boxing), they should follow a carefully periodised training and nutrition programme to ensure they maintain lean muscle mass and healthy immune function, while also observing peaks in strength and endurance for important competitions.
5. Hydration, hydration, hydration – and yes, growth hormone!
Another relatively underestimated and ill-respected practice is the maintenance of hydration status, particularly during and immediately after training.
Participants of prolonged exercise tasks have long been advised to consume fluids during exercise, but athletes rarely ingest sufficient quantities during competition to completely offset dehydration, with as little as 2% loss of body mass causing unnecessary physiological strain and a reduced endurance performance (17).
When body fluid is decreased, feedback mechanisms to the hypothalamus result in the urge to consume fluids which then, in turn, offset sensations of thirst. However, it is important to note that these efferent pathways are activated in response to dehydration, i.e. the sensation of thirst kicks in when you are already substantially dehydrated, by which time you could be experiencing a decline in performance. The advice to athletes here is somewhat of a tautology.
Yet regardless of the direct performance implications of the need to maintain body fluid, there is mounting evidence that dehydration can negatively impact the exercise-induced growth hormone response. Research by Peyreigne and colleagues (18) studied the effect of dehydration on the growth hormone response during stationary cycling in a group of healthy male volunteers.
They found that a relatively modest drop in body fluid (500ml, equating to 0.5kg bodyweight) significantly attenuated growth hormone concentrations during exercise. The same GH that mediates carbohydrate and fat metabolism, and predicates muscle recovery through enhanced protein synthesis.
Another more detailed study (19) published in the Journal of Applied Physiology, found that dehydration significantly increased circulating cortisol (the stress hormone) which inhibits protein synthesis in the muscle, and significantly reduced circulating testosterone, the actions of which are largely synergistic with growth hormone.
Depending on the type and duration of exercise undertaken, up to 150ml to 250ml of fluid every 15 to 20 minutes during physical activity has been proposed in order to retard the likelihood of a drop in body fluid (20).
However, athletes are recommended to experiment with various strategies based on their own levels of tolerance and perceptions of thirst.
6. Post-exercise carbohydrate intake – carbs are your friend
Most athletes and coaches are aware of the need for post-exercise protein ingestion. In addition, a reasonably large intake of high glycaemic index (GI) carbohydrate (60g to 90g or 1.5g per kg bodyweight), combined with the recommended quantities of protein have been shown to induce a rapid and relatively sustained increase in plasma insulin concentration, resulting from insulin secretion from the pancreas.
Insulin positively influences protein synthesis by affecting the transport of two important growth factors – insulin-like growth factor (IGF-1) and growth hormone.
Insulin-like growth factor has an important influence on cell signalling pathways and is a natural stimulus for cell growth and multiplication. It also mediates concentrations of growth hormone, the anabolic effects of which have been discussed. Needless to say that the combined actions of IGF-1 and GH augment muscle, bone and connective tissue growth and remodelling.
A 1998 study published in the Journal of Applied Physiology (21) saw a group of resistance-trained men consume pre- and post-resistance-training carbohydrate/protein supplements, or a placebo. It was observed that supplementation resulted in elevated glucose and insulin concentrations, relative to placebo, in addition to higher IGF-1 and significantly elevated GH concentrations. It was concluded that protein-carbohydrate supplementation before and after training, alters the metabolic and hormonal responses to consecutive days of heavy resistance training.
A similar study by Chandler and Byrne (22) concluded that nutritional supplements consumed following weight-training can produce a hormonal environment during recovery that may be favourable to muscle growth. This may be attributed to elevated concentrations of insulin and growth hormone.
Insulin’s other functions are to facilitate glucose uptake into muscle and liver cells to replace depleted glycogen stores, promote free fatty acid (FFA) storage into adipose sites around the body, and mediate amino acid (AA) metabolism by promoting protein synthesis and reducing its breakdown (23).
The athlete should endeavour to stimulate these important hormonal pathways following exercise by appropriately manipulating pre- and post-exercise nutrition.
Given the time and effort we devote to training in pursuit of our athletic endeavours, it is prudent we take steps to optimise our recovery. Indeed, anything less than optimal may render our efforts somewhat ineffective.
The advice presented here is anchored in evidence-based research and, as such, has proven efficacy in the context of improved recovery. Although healthy eating and effective sports supplements can be costly, most of the above recommendations (fluid, training structure, sleep) are costless, easily performed lifestyle factors that require nothing more than a little research, planning and consideration.
Nick Tiller is a BASES accredited physiologist, specialising in respiratory physiology, middle- and ultra-distance sports performance. He has worked with Olympic performance programmes in London and the South East of the UK, and is a PhD researcher at Brunel University.
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