Intervals again, and some thoughts about cross-training

Today I resumed moderate intensity running sessions after a period of lower intensity training due to a respiratory infection and its aftermath. I did a 4x1Km interval session on the riverside path, aiming for mean HR 142 (around 90% of HR maximum for an old-timer like me). On the first repetition, the breeze was behind me and I went too fast (4:13 per Km, with mean HR 145) but then settled down well to achieve mean HR 142 on the subsequent three repetitions, giving an overall mean HR of 143 and mean pace of 4:20 /Km. This is similar to my performance a week before I was smitten with a respiratory tract infection in early December, when I achieved a mean pace of 4:21 /Km at mean HR 142 in a 6x1Km session. Today’s session felt a little harder – probably because I had started too fast – but overall, I am pleased that I have not suffered any appreciable loss of fitness during my period of illness and convalescence. In fact I hope that my aerobic base fitness might actually have improved a little as a result of the relatively large volume slow running over the holiday season.

During my convalescence I have also done an increased amount of cross training on the elliptical cross trainer. The elliptical cross trainer is probably an excellent mode of exercise for non-athletes who wish to maintain a moderate level of aerobic fitness with minimal risk of injury. However, it is not clear how useful it is for runners. The available evidence is sparse. One study from the Human Performance Lab at Appalachian State University indicates that performance in a 3Km time trial deteriorated by 48 seconds during 5 weeks of elliptical training that included one lactate threshold interval session, one sprint session and 3 or 4 easier sessions per week, but no actual running. A comparison group who did ‘off season’ running training during the 5 weeks actually improved their 3K run time by a small amount (9 seconds – not a statistically significant improvement, but certainly not a deterioration). So it is unlikely that the elliptical alone is much use for preparing for a race (Honea and Dumke, http://www.osr.appstate.edu/present/documents/Honea-student_research_poster.ppt).

However, my own preliminary observations led me to wonder whether or not the elliptical might have a useful role. I found that I reached ventilatory threshold at a lower heart rate (and greater perceived effort) on the elliptical compared with running. My first impression was that this merely confirms that elliptical cross-training is a less enjoyable way of getting out of breath. This conflicts with the claims of the manufacturers who emphasize that perceived effort is less on the elliptical, but I think those claims mainly apply to non-runners working at a level well below lactate threshold, where the smoothness of the ‘ride’ is indeed quite relaxing.

But I was intrigued to understand why the ventilatory threshold appears to occur at a lower heart rate. This suggests that more lactate is produced at a given heart rate, implying that anaerobic metabolism of glucose kicks in at a lower heart rate.

To investigate this further I searched the sport medicine literature and found a recent study by Garlatz and colleagues from Western Washington University (The FASEB Journal. 2008;22:1175.2). In a group of trained distance runners they found that at 90% of Working Heart Rate Range, perceived effort was higher but oxygen consumption lower on the elliptical cross-trainer compared with the treadmill. This confirms my own observation, and strongly supports the hypothesis that there is a higher proportion of anaerobic glucose metabolism at this heart rate on the elliptical.

In retrospect this is easy to understand. The action of the elliptical involves a strong push, especially by quadriceps which are active though most of the gait cycle, whereas the quads are only active for a small part of the gait cycle when running.  However when running the quads suffer a lot of stress because they work hardest when being stretched at footfall – and this generates the micro-tears that might cause DOMS the next day. In other words, on the elliptical, the quads do more work but it is different in nature and potentially less damaging in comparison with running. It is likely that the additional work recruits a higher proportion of fast twitch fibres which tend to metabolise glucose anaerobically. Thus elliptical cross training might be a very good way to improve the body’s capacity to handle lactate with relative little damage to muscles.

If you want to run a fast 3K, you really need to train your muscles to cope with large eccentric loading. The elliptical is probably not much use for this but may nonetheless have a useful role to play in improving the capacity to metabolise lactate with minimal damage to muscles.

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One Response to “Intervals again, and some thoughts about cross-training”

  1. Ewen Says:

    That was very interesting reading. Could it be that most runners’ quads are not aerobically conditioned? I know that when riding the bike (which I don’t do much) the perceived exertion is high, yet the HR is low (around 70%). The relatively weak quads are doing most of the work.

    It looks like the elliptical trainer would be as good (or better) than cycling for cross-training, but easy running might be better ‘cross-training’.

    The large volume slow running that you’ve done is also interesting. My theory is that it doesn’t matter how slow the running is, as a means of strengthening the cardio-vascular system. For specificity though there needs to be some running at, above and below race-pace.

    What do you think of the following method of comparing general aerobic runs:
    If the total number of heart-beats in the session above ‘standing HR’ are the same, then the runs have the same value. In other words, a run of 60 minutes @ AHR 80% might be equivalent to a slow run of 75 minutes @ AHR 70%?

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