In the early years of a runner’s career, almost any reasonably sensible training plan with a gradual build-up of training load will produce improvement. However, once a runner has reached a plateau of performance, the challenge is to identify the type of training that offers the best chance of further improvement. Races ranging from 5K to marathon are run at paces in the vicinity of lactate threshold (LT). Race performance is largely determined by the fact that as pace rises above lactate threshold, acid accumulates in muscles and blood, eventually resulting in an enforced slow-down. Thus, one of the major goals of training is increasing pace at lactate threshold, as this will allow increased race pace. The principle of specificity of training suggests that the optimum training program will include a large amount of running near lactate threshold to enhance capacity to prevent accumulation of acid. Indeed, this is the approach adopted by many recreational runners.
However, the evidence from examination of the training logs of elite endurance athletes, reviewed comprehensively in a lecture by Stephen Seiler in Paris in 2013, indicates that many elites adopt a polarised approach that places emphasis on the two extremes of intensity. There is a large amount of low intensity training (comfortably below LT) and an appreciable minority of high intensity training (above LT). Polarised training does also include some training near lactate threshold, but the amount of threshold training is modest; typically the proportions are 80% low intensity, 10% threshold and 10% high intensity.
As reviewed in my previous post on the topic, several scientific comparisons of training programs have demonstrated that for well-trained athletes who have reached a plateau of performance, polarised training produces greater gains in fitness and performance, than other forms of training such as threshold training on the one hand, or high volume, low intensity training on the other.
The specificity principle
Nonetheless many coaches and athletes who advocate specific training paces to achieve the various required adaptations required for distance running, maintain a firml belief that threshold training is the best way to increase the pace at lactate threshold, and should form a substantial component of a distance runner’s training program. Jack Daniels, doyen among coaches advocating specific paces for specific adaptations, has argued that because stress level rises rapidly at paces exceeding threshold there is a sweet spot in the vicinity of lactate threshold that achieves sufficient stress to promote adaptation while avoiding the danger of excessive stress.
Evidence from laboratory studies of rats appears to provide some support for this view. While it is necessary to be cautious in using evidence from studies of rats to inform training of humans, the basic physiology of rat muscle is similar to that of human muscle. They share with us an aptitude for running at aerobic paces. The evidence from the well-controlled systematic studies that are feasible in rats is potentially useful in establishing principles that apply across species. Dudley’s studies in which he measured changes in aerobic enzymes produced by a variety of different training intensities and durations in rats (all training for 5 days per week for 8 weeks) demonstrated that running beyond a certain duration produced no further increase in aerobic enzymes. Furthermore, the duration of running beyond which there was no further improvement is shorter at higher training intensity. This suggests that at any given intensity, training runs beyond a certain duration will produce no further increase in aerobic capacity though there might of course be other gains, for example increase resilience of bones, muscles, ligaments, tendons and also the mind. But there is also likely to be an increase in overall stress. At very high intensity the duration limit is so short that the overall gain in aerobic fitness is less than can be achieved by longer session at lower intensity. The greatest overall increase in aerobic enzymes in muscles with predominantly red (aerobic) fibres, was achieved by an intensity that led to maximum gain at around 60 minutes. Thus in Dudley’s rats, there appeared to be a sweet spot in intensity for optimum development of aerobic capacity. Although Dudley did not measure lactate levels, it is plausible that this intensity corresponds roughly to lactate threshold in humans.
Hormones and training
However even if we accept that Dudley’s studies support Jack Daniel’s argument for a sweet spot, it is crucial to note that Dudley assessed the effects of training over a total duration of only eight weeks. The important issue for the athlete who has reached a plateau is the likely consequences of training over a longer time-scale than 8 weeks. It is probable that the crucial issue is the balance between catabolic and anabolic effects of training. During a training session, the catabolic hormones cortisol and noradrenaline are released into the blood stream to mobilise body resources, especially glucose, required to meet the demands of training. The release of catabolic hormones also triggers the subsequent release of anabolic hormones, such as growth hormone, that promote repair and strengthening of body tissues. As training intensity rises above lactate threshold the release of catabolic hormones and the associated release of anabolic hormones increases sharply (as illustrated by Wahl and colleagues). Thus the potential stimulus triggering the benefits of training rises sharply as intensity exceeds lactate threshold. The accumulation of cortisol also increases with increased duration of running. For example, Cook and colleagues report that salivary cortisol increases steadily during a marathon, typically achieving a fourfold increase at 30 minutes after completion of the race compared with the level prior to the start.
While a transient rise in cortisol tends to be beneficial, sustained elevation of cortisol is potentially harmful because cortisol promotes the breakdown of body tissues. Cortisol levels in hair samples provide an indication of cortisol level sustained over a period of weeks or months. Skoluda et al measured cortisol levels in hair in a group of distance runners over a season. They reported that these runners had abnormally high cortisol levels over a prolonged period, raising the possibility of adverse sustained catabolic effects, including suppression of the immune system. Skoluda concluded that repeated physical stress of intensive training and competitive races is associated with potentially harmful sustained elevation of cortisol. However, they did not explicitly compare different training programs.
There is no published evidence of differences in medium or long term catabolic/anabolic balance between polarised training and threshold training. Furthermore, because gradual increase in training load leads to a blunting of the sharp rise in catabolic hormones produced by training in the vicinity of LT, a fully informative study would need to take careful account of the structure of the training program over a sustained period. Nonetheless a study of high level distance runners by Balsalobre-Fernandez and colleagues does provide relevant information. They recorded training, performance and salivary cortisol level in 15 high-level middle and long-distance runners from the High Performance Sports Center, Madrid, throughout a period of 10 months. The group comprised 12 men and 3 women, mean age 26.4 years, with personal bests in 1500-metres between 3:38–3:58 (men) and 4:12–4:23 (women). They rated training in three zones: zone 1 included long-distance continuous training, or interval training with long sets (4–6 km), at relatively relaxed paces; zone 2 included of intervals with sets of 1–3 km at approximately 5 K pace , likely to be moderately above lactate threshold; zone 3 included short-distance and sprint interval training at paces ranging from around 1500m pace to full sprint. Thus zone 1 and 3 roughly correspond to low intensity and high intensity zones of a polarised program, while zone 2 sessions are a little more intense but less sustained than a typical threshold training session in the mid-zone of a typical polarised program.
During the winter months, the athletes did a substantial amount of low intensity (zone 1) training. The 25 weeks of spring and summer training was dominated by zone 2 training. For 15 weeks within this 25 week period, the average training zone was in the range 1.75-2.25, indicating a large proportion of zone 2 training; while for 3 weeks the average was above 2.25, indicating an appreciable amount of training in zone 3 in addition to zone 2.
In addition to recording race performance, Balsalobre-Fernandez and colleagues regularly assessed vertical counter-move jump height (CMJ) as a measure of neuromuscular performance. Averaged over the entire season, the runners with higher long-term cortisol levels has significantly lower CMJ scores, confirming that sustained elevation of cortisol is associated with poor neuromuscular performance. However, analysis of correlations between weekly average cortisol and CMJ values revealed that higher CMJ scores were recorded in weeks with higher cortisol levels, indicating that transient elevation of cortisol is associated with better neuromuscular performance. The weeks with higher CMJ performance were weeks with lower training volume but higher training intensity (i.e. more Zone 3 sessions). Finally, CMJ scores were significantly higher in the week before the season’s best competition performance
In summary, the evidence from the study by Balsalobre-Fernadez and colleagues confirms that sustained elevation of cortisol is harmful and favours a lower volume of higher intensity training rather than moderately large volume a little above lactate threshold. This might be a key to understanding why polarised training might be superior to threshold training. In my next post, I will examine the mechanisms by which the training adaptations required for distance running might be best achieved using a polarised approach. In particular I will discuss the ability of negative ions such as phosphate and bicarbonate in the blood to provide temporary buffering of the acidity associated with lactate production. This buffering might allow transient surges of lactate produced by brief high intensity exercise to produce beneficial enhancement of the transporter molecules that facilitate transport of lactate from type 2 to type 1 muscle fibres in which it can be used as fuel, and also the transport of lactate from muscles to liver and heart, without the potentially damaging effects of increased acid levels associated with sustained increase in level of lactate.