Transfer of the benefits of elliptical cross-training to running

As usual, Ewen raises the important question about my post yesterday about improvements in aerobic efficiency during 3 months of elliptical cross training.  He asks whether or not the observed improvement would be expected to result in a lower heart rate in the vicinity of lactate threshold when running.  Implied in this question is the more general question: will the observed improvement in aerobic fitness lead to improved performance when running.  I do not know.

 

The definitive proof of the pudding will come when I test myself in a race.  However, many factors affect race performance. In my case, my tendency towards asthma places me at the mercy of my only partially controllable bronchi, so a particular race might be more influenced by daily fluctuations in the irritability of my bronchi than by overall change in aerobic fitness.  Therefore I need a test that is relatively unaffected by variable outside air temperature and humidity, and the muddiness of the terrain; and furthermore, produces little DOMS so it can be applied fairly frequently, allowing averaging to minimize the effect of daily fluctuations.  That is why I developed this elliptical test for aerobic fitness.  The dilemma is that I can only speculate on the likelihood that the gains in aerobic fitness on the elliptical will transfer to fitness for running.  I am still evaluating the relevant evidence, but here are my currents thoughts.

 

The goals of aerobic conditioning for running are:

1)      Increasing the number of mitochondria in muscle fibres. The mitochondria contain the enzymes that carry out oxidative metabolism; that is the combining of glucose with oxygen to generate relatively large amount of energy.  Increasing mitochondria should increase the ability to generate energy efficiently, provide enough oxygen and glucose can be delivered to the muscles.

2)      Increasing the efficiency of the heart as a pump.

3)      Promoting development of new capillaries in muscle so that blood (and hence oxygen and glucose) can be delivered to muscle fibres at a higher rate.

4)      Increasing the ability to metabolise lactate.  When the rate of supply of oxygen is insufficient, energy is produced by anaerobic metabolism  in which glucose is converted to lactate.  Although  this process is the dominant process once the ‘anaerobic threshold’ is exceeded, in fact this threshold is not an all-or-nothing threshold.  In the upper part of the aerobic zone, when oxygen delivery is not quite adequate, a certain amount of lactate is produced.  Build up of lactic acid leads to eventual transition into the anaerobic zone that can only be sustained for a limited time before rising acidity impairs muscle function.  This build up might be delayed if the ability of muscles and perhaps other tissues to remove lactate, is increased. In fact, lactate is also oxidized in mitochondria, so enhanced mitochondrial function should help delay the build up of lactate.

5)      Improving neuromuscular efficiency – the ability of the central nervous system to recruit muscles in the most efficient manner.

6)      Re-modelling of tendons, ligaments and bones to withstand the stresses of running

7)      Hypertrophy of muscle fibres.  During aerobic conditioning, I believe that the main mechanism of increase in the strength of muscle is likely to be the increase in mitochondria and capillaries listed above; during anaerobic resistance training, hypertrophy is due to incorporation of additional protein into muscles.  It is nonetheless probable that some strengthening of contractile proteins occurs during aerobic conditioning.  The skinny legs of many elite distance runners suggests this strengthening makes only a minor contribution to fitness for distance running, but even a distance runner needs to be able to exert  at least a moderaltey powerful downwards push at the end of stance because elastic recoil is far from 100% efficient and therefore elastic recoil is unable to supply an adequate push to propel the body along the required trajectory in the airborne phase. 

 

So which of these processes is likely to be enhanced by elliptical cross training, which are likely to be unaffected and which might actually be harmed?

 

Development of the heart as a pump is likely to be similar for a similar work elliptical work load as for running.  Development of mitochondria and capillaries is also likely to be similar, though  there is a possibility that the development will be a little more focused on fast twitch fibres, because the concentric contractions characteristic of the elliptical training are a little to likely to recruit fast twitch fibres. The development of ability to metabolise lactate is likely to be similar for the two types of training.

 

Elliptical training is unlikely to be effective in fine tuning of neuromuscular coordination for running.  The ability to capture the gravitational energy associated with the vertical oscillations of running, in the from of elastic energy that can be recovered at lift-off, is a crucial factor in efficient running.  The elliptical does not develop the exquisite neuromuscular coordination required for this.  Similarly, elliptical cross training does not provide much stress on tendons, ligaments  and bones, and hence will not be very effective in remodeling these structures to withstand the stress of running.  On the other hand, as I discussed in my post about reactive oxygen on February 5th,  the benefits of running might be offset by permanent damage to muscle fibres.  Such permanent damage appears to be less likely with elliptical training on account of the lesser amount of eccentric contraction.

 

Finally, I suspect that elliptical training might actually produce greater hypertrophy of muscle due to incorporation of protein in the contractile machinery with the muscle fibres, than running.  Because there is minimal elastic recoil, the elliptical demands a stronger downwards push by the leg muscles. I suspect that this will be more effective in producing hypertrophy of fast twitch fibres.  Too much hypertrophy of fast twitch fibres might be harmful, though at least for oldies like myself, in whom deterioration of fast twitch fibres is likely to play a major part in the shortened stride that makes us slow, I think a moderate amount of development of fast twitch fibres is probably beneficial.

 

Summary

So in summary, elliptical cross-training is likely to increase the pumping capacity of the heart, increase mitochondria and capillaries in muscle and increase the capacity to metabolise lactate.

 

It is unlikely to do much to strengthen tendons, ligament ad bones, but on the other hand, is also much less likely to cause permanent damage to either these connective tissues or to muscles.  It will not refine the exquisite neuromuscular control required to capture gravitational energy as elastic energy, and to recover via recoil at lift-off when running.

 

It might promote a slightly greater degree of hypertophy of fast twitch fibres than an equivalent amount of running.  I am inclined to think that on balance this might be beneficial, especially for older runners.

 

As Ewen suggests, it might be useful to replace the training session the day before a high quality running session with an elliptical session to help ensure that the muscle are in good shape for the high quality session.  However, in the warm up for the quality session, it is probably all the more important to include some brief bursts of running at the quality training pace, so as to recover optimal neuromuscular coordination for running at that pace.

 

Most of this is speculation.  I hope that when the spring arrives my bronchi will allow me to assess the fruits of my elliptical sessions, in a 10K race.

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One Response to “Transfer of the benefits of elliptical cross-training to running”

  1. Ewen Says:

    Fascinating reading once again. Even though you say your conclusions are speculation, they do seem logical.

    It’s particularly interesting about neuromuscular coordination being different on the elliptical trainer. I was thinking about that. I’m presuming the tempo (number of ‘strides’ per minute) is much slower than for running, as well as there being no ‘recoil’ from the foot landing on the ground as in running.

    With training, could it be possible for the brain to efficiently ‘switch’ between the neuromuscular requirements of the two forms of exercise? What makes me think that it’s possible, is my own experience with short sprints, or short steep hills. Even though I only do them once per week (or less), there is no deterioration (and sometimes improvement) in my ability to do them. The short sprints have a different neuromuscular requirement to slow easy aerobic running.

    The hypertophy of fast twitch fibres is also interesting, and as you say, of particular benefit to older runners. How well can these fibres be recruited aerobically? Or do they mainly provide ‘support’ for slow twitch fibres?

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