High-strung gnus

We stopped to let a herd of wildebeest cross the road in front of us. Wildebeest are skittish creatures. They were crossing for a while before we came along, but a few began to hesitate when they saw us. Others kept crossing, and eventually the warier individuals figured that we were unlikely to harm them and stepped on to the road.

There was a ditch on either side of the road. The gnus would tumble down one, halt, and then slowly amble across the road. As they came to the other ditch, they would spring across it. Muscles in humans, and other mammals, come in two types: slow-twitch, also called type I, and fast-twitch, called type II. A springing action requires fast-twitch muscles. At the time that I started trying to lose weight, I learnt that some type II muscles must be exercised to use up glycogen stored by your liver, and type I muscles must be used a lot to burn fats that your body has stored. That’s the difference, my trainer explained, between aerobic exercise and intense short duration exercise.

These leaping gnus were using their fast-twitch muscles. I was fascinated, and snapped off a long series of shots. You can see that their hind legs are nearly stationary as their forequarters go into motion: that’s why the back legs are in focus even as the front of the body is blurred by motion. Blue wildebeest weigh between 250 and 300 kilos, so these muscles must be fantastically powerful. I came across a study of muscle chemistry in the related black wildebeest (Connochaetes gnou) which found that their fast-twitch muscles have highly efficient structures able to do anaerobic exercise much better. That explains these leaps.

Once they are spurred into action, the gnus don’t stop running. I’d seen that earlier during their river crossing, and now I saw a minor stampede again. The survival tactics behind this is clear, but is it really good for the animal in the long run? The Family and I had been talking about the stress hormones that must be flooding into a gnu’s body all the time, and asking ourselves whether they shorten its life. It probably does, because gnus seem to live twice as long in zoos as the oldest ones seen in the wild. But still, this kind of extended running requires very efficient type I muscles, and that is exactly what this paper reported. I was right in paying so much attention to wildebeest, they may look like jokers, and behave like them, but they are champions. Raj Kapoor would have understood this.