Archive for October, 2014

Getting maximum benefit from low intensity training

October 3, 2014

In my recent posts I have discussed the evidence suggesting that if one’s goal is year-on-year improvement in marathon performance, the best approach is a polarised program including a large volume of low intensity training and a small volume of high intensity training. Since at least 80% of the training time during a polarised program is devoted to low intensity runs, it is worth considering how to derive the greatest benefit for these sessions.

First, I should make it clear that I believe in a periodized approach that includes a base-building phase and a race-specific phase. Both phases should be polarised, each embracing both low intensity and high intensity training. In the base-building phase, the goal is to build all of the basic physiological capacities required for marathoning. In this phase, the low intensity sessions play a crucial role in developing several of these capacities, but high intensity sessions also play a key role. In the race-specific phase a small proportion of the sessions are devoted explicitly to developing the mental and physical strength required for racing. This post will deal mainly with the base-building phase. Nonetheless, even in the race-specific phase it is crucial to maintain the capacities developed during base-building, so many of the principles apply to planning training in both phases. I will address the specific requirements of race-specific phase in greater detail in a future post.

In my post of 20th September I listed the five physiological capacities that need to be trained in preparation for a good marathon:

  • VO2max – this measures the maximum rate at which oxygen can be delivered to tissues and hence the maximum rate at which muscles can generate energy.
  • Speed at VO2max.
  • Pace at lactate threshold as a proportion of pace at VO2max. For a well-trained marathoner, race pace is near to lactate threshold.
  • Ability to conserve glycogen so that glucose supply is not exhausted before 26.2 miles.
  • Resilience of leg muscles to sustain pounding for the duration of the marathon with only minimal loss of power.

Each of these five capacities can be enhanced by several different types of training stimulus, so full development each of the variables requires a complementary mix of low and high intensity training. The low intensity session play an especially important part in increasing three of the five capacities: VO2max; conservation of glycogen; and developing resilience of leg muscles, so we should consider each of these in turn.

Enhancing VO2max

The two major ways in which low intensity training enhances VO2 max are by increasing the aerobic enzymes in mitochondria; and by enhancing the capillaries that deliver blood to muscle fibres. These physiological processes can be examined in muscle biopsies from athletes, but more detailed information can be obtained from the study of animals. Despite the large scale anatomical differences between the human and rodent musculo-skeletal systems, at the level of individual fibres the structure and functional of muscles are similar across the species so studies of the ways rodent muscle fibres respond to training are likely to be informative about the ways in which human fibres respond.

One of the major questions in planning a training schedule is whether it matters whether the training is done in multiple short session or fewer long sessions. The long slow run has been regarded as a core feature of marathon training for years, though the data for study of animals suggest that with regard to enhancing aerobic enzymes and capillaries, multiple short runs might be just as beneficial.

In a recent study. Malek and colleagues trained mice on a treadmill on 5 days a week for 8 weeks. One group of mice trained for 30 minutes continuously on each training day, while another group of mice trained for 3 periods of 10 minutes separated by a 2 hour rest. The intensity of training was equal.  The animals started at the rather slow pace of 7.5 metres per minute, and over the 8 weeks, increased the rate of working up to 60% of maximum power output. A control group of mice were placed on the treadmill but did no training. Compared to the untrained controls, both groups of trained mice exhibited similar major improvements in both speed and distance covered during an incremental treadmill tests administered at the beginning and end of the training period. The untrained controls exhibited a 1% increase in the distance covered in the incremental test after 8 weeks, while the group who trained continuously for 30 minutes exhibited an increase of 107% and the group who trained for 3×10 minutes exhibited an increase of 117%. . Furthermore, after training, the capillary density and the number of capillaries per muscle fibre in quadriceps muscle were approximately twice as great in the two training groups compared with the untrained controls. Similarly the amount of the aerobic enzyme, citrate synthase, in the plantaris muscle in both of the trained groups was about twice as great as in the controls. Thus, running performance, muscle capillary density and aerobic enzymes showed large, but similar, increases in both trained groups. This suggests that with regard to improving VO2max , three 10 minute training sessions produce very similar enhancement to one 30 minute training session.

On the other hand, Dudley’s well known studies, in which he trained rats at several different speeds for varying lengths of time per day showed that very long sessions did not produce greater enhancement of aerobic session that medium length sessions. The greatest gain in cytochrome C (a complex of aerobic enzymes) occurred in rats trained at a pace of 30 metres/min. Thirty metres/min is a medium pace for a rat; typically a rat can maintain 60 metres/min for about 10-15 minutes whereas it can sustain 30 metres/min for an hour or so with little difficulty. The rats that trained at 30 m/min showed a steady increase in enhancement of cytochrome C in red soleus muscle with increasing daily run time up to 60 minutes, but the there was only a slight further training effect in the group who trained for 90 minutes, suggesting no benefit with regard to aerobic enzymes beyond 90 minutes..

It is important to note that Dudley’s rats did not have much opportunity to adapt to the training load.   After an initial five day introductory period of running 5-10 minutes daily at approximately 30 m/min, they were allocated to the designated training and the training load was ramped up at the rate of 12 additional minutes each day, ensuring that the animals allocated to train for 90 minutes per day were training at full load by the end of the second week. It is possible that the rats allocated to 90 minutes per day at a pace of 30 m/min were not given adequate time to adapt to the training load. Inadequate adaption to the load would be expected to result in excessive release of cortisol which has a damaging catabolic effect on muscle.

Taken together, the findings from Malek’s study of mice and Dudley’s study of rats, indicate that there is little difference in the training benefit derived from a single continuous session of 30 minutes compared with three session of 10 minutes, while the benefits of increasing the length of sessions beyond 60 minutes are small in the absence of an adequate period to adapt to the training load. It is speculative, but I consider quite plausible that provided long run duration is built up gradually, that additional benefit will accrue beyond 90 minutes. Nonetheless, with regard to enhancing erobic capacity, the evidence suggests that multiple short runs are likely to be at least as effective as a similar total duration of long runs. This would suggest that for VO2max development, doubles might be at least as effective, and perhaps more effective in terms of time spent and stress sustained than single daily sessions. However, enhancing VO2max is not the only goal of training.

Enhancing conservation of glycogen.

Endurance training produces an increase in the proportion of energy derived from fat, across a wide range of intensity of exercise. Although it is well established that in both trained and untrained individuals, the proportion of energy derived for fat is less at paces above lactate threshold than at paces below threshold, nonetheless, even above threshold, trained athletes derive a larger proportion of total energy from fat than untrained individuals. [See the opinion piece by Coggan.]

While many studies have demonstrated that trained individuals derive a greater proportion of the energy required during exercise from fat, compared with untrained individuals, there have been only a few longitudinal studies that have demonstrated the efficacy of a specific endurance training schedule for enhancing fat metabolism. One particularly informative study was done by Henriksson. He subjected 6 cyclists to a training program in which only one leg was trained for 45 min/day at 70% of VO2max (estimated for one leg) for an average of three days per week for a period of 8 weeks.

Before and after the training period, a muscle biopsy was taken from quadriceps for determination the activity of the aerobic enzyme, succinate dehydrogenase. The subjects were also tested on different submaximal and maximal one-legged and two-legged workloads. Catheters were inserted into the femoral arteries and veins at the groin in both legs to allow measurement of blood oxygen and carbon dioxide levels. In the submaximal test, participants performed two-legged exercise for 1 hour at 67% of VO2 max.  In the trained leg, there was a substantial greater capacity of muscle to extract oxygen from blood, demonstrated by increased arterio-venous difference. The respiratory exchange ratio (RER) was 0.91 throughout the 1 hour in the trained leg. Respiratory exchange ratio is the ratio of the amount of CO2 produced to O2 consumed. It has a value of 1 when carbohydrate is the sole fuel and a value less than 1 if fat is included in the fuel mixture. Thus the value of 0.91 indicates that a substantial proportion of energy was obtained from fat. In contrast, in the untrained leg, RER after 10 minutes was 0.96 indicating that the majority of the energy was obtained from carbohydrate metabolism and even after 50 minutes, the RER in the untrained leg was 0.94. Thus the proportion of energy derived from fat had increased as might be expected if glycogen stores were being exhausted, but nonetheless even after 50 minutes the proportion of energy derived from fat in the untrained leg was less than in the trained leg.

Henriksson estimated that in the trained leg, 42% of energy was obtained from glycogen while in the untrained leg, 62% of energy was derived from glycogen. Thus, the increased utilization of fat in the trained leg resulted in appreciable conservation of glycogen. Furthermore, rate of lactate release in the untrained leg was between 2.5 and 3 mmol/min in the period from 10 to 30 minutes yet remained below 0.5 mmol/min in the trained leg, confirming the expectation arising from the fact the fat metabolism does not generate lactate.

It was also of interest to note that measurement of free fatty acids in the blood demonstrated that the increase fat metabolism came largely for increased consumption of triglycerides stored within muscle. The mechanism of this increase was not clear. The activity of aerobic enzyme succinate dehydrogenase increased in the trained leg. This increase in aerobic enzymes would lead to faster fat metabolism. However it is probable that an increase in enzymes involved directly in fat metabolism and also an increase in ability to transport fats into mitochondria played a part

In summary, the study by Henriksson established that moderate intensity exercise (70% VO2max) for 45 minutes 3 days per week produced a substantial enhancement of fat metabolism, thereby conserving glycogen and reducing the production of lactate.   He did not address the question of whether or not a greater benefit would have been obtained from longer duration of exercise. However the observation that even in the untrained leg the proportion of energy derived from fat increased appreciably by 50 minutes confirms the expectation that a long duration low intensity session would be more effective for enhancing fat metabolism than multiple short duration sessions.

Thus, it is likely that long runs lasting an hour or more are the most effective for increasing fat metabolism, but it is necessary to bear in mind that unless long run duration is increased gradually, there is a risk of increased release of cortisol. Similarly, training in a fasted stated would be expected to produce greater enhancement of fat metabolism but care should be taken to avoid excessive stress. As I suggested in my previous discussion of training in the fasted state, I suspect that the inconsistent results reported by different studies of training in the fasted state reflect differences in the degree to which there was adequate adaptation to training in a fasted state.

Resilience of leg muscles

Eccentric contraction at foot strike causes microscopic tearing of muscle fibres. This is likely to be the major factor in the production of Delayed Onset Muscle Soreness (DOMS). However, as virtually every athlete knows from direct experience, after DOMS, the muscle adapts rapidly to prevent subsequent damage if the same exercise is repeated.

Although many recreational athletes preparing for a marathon experience some DOMS early in the program, they quickly develop sufficient resilience to prevent serious DOMS in subsequent weeks. However, the observation that many experience a recurrence of severe DOMS in the aftermath of the race itself, indicates that they failed to develop adequate resilience to cope with the sustained pounding of the marathon.   While a few days of DOMS after the event might be of little consequence, the effect of microscopic damage during the event is potentially of much greater importance. Muscle damage during the marathon appears to be one of the major causes of slowing down in the second half of the race. Therefore, development of adequate resilience is a high priority.

During the race itself it is the combination of the duration of the stress and the intensity of stress that does the damage. It is therefore likely that a multi-facetted approach, involving both long duration sessions and some more intense running is required to build the required resilience. An approach that relies too heavily on extending the duration of intense exercise would be risky. Although complete recovery from DOMS is usual provided there is adequate subsequent opportunity for recovery, if there inadequate opportunity for recovery, the muscle might eventually lose its capacity to recover. It appears likely that the relatively rare Fatigued Athlete Myopathic Syndrome (FAMS) is the end stage of repeated microscopic muscle trauma without adequate opportunity for recovery. In cases of FAMS the athlete exhibits marked disruptions of muscle microstructure and suffers loss of the ability to tolerate further training.  On the other hand, repeated exposure to a small stress can protect against future larger stresses, so long slow runs are the safest way to establish the foundation for the resilience required to withstand the repeated pounding at marathon pace

Conclusions

The evidence provides very strong grounds for arguing that a substantial volume of low intensity training is an effective complement to a small volume of more intense training during marathon preparation. In particular, the low intensity training is a safe way of enhancing VO2 max; promoting the ability to conserve glycogen (and incidentally reducing the production of lactic acid); and lays the foundation for the muscle resilience required to avoid slowing in the later stages of the race.

This evidence also provides guidance regarding how best to schedule this training. The first point to note is that multiple short session are likely to effective in enhancing VO2max in a safe manner. However, at least some longer duration sessions are also required to optimise the ability to conserve glycogen via utilization of fat, and to develop the required resilience.

The traditional answer to these requirements is to incorporate a weekly long run of gradually increasing length in the training schedule. This traditional answer certainly has merit. However, it is possible that this strategy relies too heavily on the weekly long run. For example, building up the long run length from less than 10 miles to more than 20 miles within the course of a 12-16 week program might not provide adequate opportunity to adapt adequately to the demands of the long run. This has two consequences. First, the long run itself might leave the runner tired and aching, limiting the quality of training on subsequent days. Secondly, there is a substantial risk that one long run per week will prove inadequate for developing the resilience required to maintain pace for the full 26.2 miles.

An alternative to placing so much of the emphasis on a single weekly long run is to add small increments to the duration of several runs each week, thereby creating a more uniform build-up of training load throughout the week and avoiding the disruptive influence of a single long run. This is the approach pioneered with great success by Ed Whitlock. He gradually built the capacity to cope with three or four 3 hour slow runs each week, in preparation for his phenomenal 2:54:48 in the Toronto Waterfront marathon at age 73. Ed acknowledges that although this worked so well for him, such an approach might not work so well for others. However, in my view the evidence we have considered in this post provides reasonable grounds for expecting that Ed’s approach might work well for others.   The evidence that capillaries and aerobic enzymes can be developed effectively in multiple relatively short sessions and that appreciable improvement in fat metabolism can be achieved with session of 45 minutes duration, while on the other hand, long sessions without adequate foundation create risk of excessive release of damaging catabolic hormones, suggests that gradual build-up of the duration of multiple longish runs each week might be effective.

It is important to note that the two crucial features of Ed’s approach are the multiplicity of long runs each week and the gradual increase in length of these long runs. While it is true that by age 73 most of his long runs were of 3 hours duration, he had built up to that duration over 6 years. When he first set a single age world record for the marathon at age 68, the majority of his long runs were only two hours in duration. He did not measure the distance of these runs, but as far as I can estimate from his own description of these easy long runs, it is unlikely that in 2 hours he ran more than 14 miles. I think that the evidence we have considered above suggests that the important feature is the consistency throughout the week rather that the focus on a single very long run each week.

There is one respect in which I am inclined to recommend a difference from Ed’s approach. His high intensity sessions took the form of frequent races over shorter distances, and occasional fartlek sessions, but no specific preparation for maintaining marathon pace throughout the race. I think that in the final 12-16 weeks of preparation for a marathon, one of the weekly long runs should be replaced by a race-specific training session aimed at developing the required mental and physical strength for racing. However I will defer detailed discussion of ways of implementing this to a future post.

I am at present working on gradually increasing the duration of four runs each week.   I started with four 65 minute easy runs in the first week of this program, and after 6 weeks have increased the duration of these four longish runs to 105 minutes each. I am also doing at least one high intensity session per week and one or two other short sessions. I am carefully monitoring the rate of increase in duration of these four runs to ensure that there is no cumulative tiredness. It is still far too early to deliver judgment on this strategy. However I have now built up to a weekly volume that is almost as high as the highest I have achieved at any time in the past few years. Last year and also the year before, I had found that after a few weeks at this volume of training I was showing signs of accumulating exhaustion and therefore was obliged to cut back the volume of training. If I continue to make small advances in run duration without accumulation of tiredness over the next few weeks I will have the first indications that this strategy is working.