Mitochondria

In other words, a rat training at about 70 to 75% VO2max could upgrade cytochrome c by expanding workout duration from 30 to 60 minutes - but not by increasing workouts from 60 to 90 minutes. This was true at all intensities studied by Dudley - and also with all three muscle fibre types. Progressing beyond about 60 minutes per workout simply didn't have much value when it came to the mitochondria.The faster you train, the betterHowever, Dudley's most interesting findings were those related to intensity of training. The Syracuse researcher was able to show that in fast-twitch muscle fibres, just 10 minutes of fast running (at close to 100% VO2max) per day was enough to roughly triple cytochrome c concentrations over an eight-week period. In contrast, running for 27 minutes at 85% VO2max daily only hoisted cytochrome c by 80 per cent, while 60 to 90 minutes at 70 to 75% VO2max nudged cytochrome c upward by just 74 per cent. So much for the theory that intense exercise can hurt mitochondria.In intermediate muscle cells (those which are roughly half-way between fast twitch and slow twitch), a similar potency of intensity was detected. For example, just 10 minutes of fast running per day fattened cytochrome c as much as 27 minutes daily at 85% VO2max or 60 to 90 minutes at 70 to 75% VO2max. One can only think that a slightly greater amount of fast running would have given speed a definite mitochondrial edge over longer-duration exertions.When it came to the slow twitch cells, however, the results were a bit different. As mentioned, running more than 60 minutes per workout had no positive effect at all on cytochrome c expansion. The best strategy for slow-twitch, cytochrome-c uplifting turned out to be running about 60 minutes per workout at 70 to 75% VO2max (or around 80 to 84 per cent of max heart rate), which hoisted cytochrome c by approximately 40 per cent. Gamboling along for 27 minutes at 85% VO2max was not far behind, producing a 28-per cent upturn. Fast running at close to 100% VO2max lifted slow twitch cytochrome c by around 10 per cent, a comparatively small gain but one that is not too surprising, given the fact that slow twitch fibres tend to be relied on less heavily than fast twitch cells during fast running. Not to belabour the point, but a 10-per cent increase is not consistent with the idea that fast training is 'hard' on the mitochondria in slow twitch muscles.And, let's face it, a 10-per cent gain in the slow twitch fibres for 10 minutes of fast running represents an improvement of about 1 per cent per minute. In comparison, running at 85% VO2max lifted cytochrome c in slow-twitch fibres by the same 1-per cent per minute rate, and chugging along at 70 to 75% improved the mitochondria by just 40/60 or 2/3 of a per cent per minute. Again, one has to think that larger amounts of fast running would have pushed the mitochondrial gains toward those observed with slower running.So what's the bottom line? As Dudley and his colleagues put it, an increase in the intensity of training brings about the greatest adaptive response in the mitochondria. Expressing the crucial importance of intensity another way, Dudley and co-workers said, 'For the same adaptive response, the length of daily exercise necessary to bring about the change becomes less as the intensity of exercise is increased.' In other words, 10 to 15 minutes of running at 5-K pace in a workout can do much more for you than running for 60 to 90 minutes at slower intensities.Realistically, of course, it's difficult to train fast every day, so almost every athlete ends up with a balance of training, with some days hard and some easy. It's nice to know, however, that to significantly upgrade your muscle-cells' mitochondria, and therefore your VO2max and average racing and training speeds, you don't have to spend hour after hour trudging along. Upswings in your training speed are generally more productive than big upturns in total mileage. Gradual increases in your training intensity - even adding just a few minutes of faster working each day - can pay off with big muscle adaptations and excellent new PBs for you!