|Wildebeest wrestling - the ultimate fitness regime? Selous GR, June 2010.|
Lions certainly can get fat - zoo keepers have to be careful to maintain the weight of captive lions within normal bounds by restricting their access to food and trying to get them to be more active through 'environmental enrichment' activities. So it's not as though they are somehow immune to such fitness concerns. So what's special about lions that helps them through this? The answer, of course, is that they do sufficient exercise: although they are pretty inactive most of the time, the effort it takes to actually catch and kill an animal is huge, even if the action only occurs for a few short seconds. During those seconds they're giving it everything they have. And if there's anything similar about their metabolism to ours, these short but extremely intense bursts of exercise are more than enough to keep a lion - or us - in good shape. In fact, the paper I read (it's free to view here) is a review of numerous studies of different fitness training regimes, focusing on comparing 'High-intensity Interval Training' (HIT) to more traditional fitness regimes. In essence, Gibala and colleagues conclude that HIT - involving just a few minutes of absolute 100% capacity exercise per week - offers comparable fitness and health benefits to much more time intensive traditional fitness regimes that raise metabolic rates (or at least Oxygen consumption) to 60 - 75% of maximum. In other words, chasing down and wrestling a wildebeest to the ground for a minute or two each day, can give you the same fitness benefit as doing an hour or so of moderate exercise each day.
|Lions do sleep. A lot!|
In fact for the lion and other large carnivores it's well known that it's not an easy life at all - obviously lions in the wild don't worry about keeping fit, they worry about meeting their energy requirements. And there's another paper that explores some of the energetic consequences of carnivory that's really rather interesting too (free to view here). This is a theoretical study exploring body size relationships and energetic costs among carnivores. This is interesting, because not only do energetic requirements scale with body size in a non-linear way (if you're bigger you need more energy than small animals, but proportionately you need less: a doubling of body mass corresponds, more or less, to an increase in energy requirements of only 1.7 times), but there's also a distinct and very, very important difference between big and small carnivores (we'll define big as anything over 20kg). Small carnivores like wild cats tend to eat lots of small things - mice, invertebrates, birds, etc - that tend to be smaller in body mass than the carnivore. But above about 20kg carnivores switch dramatically, preferring to prey on animals that are as big, or bigger than themselves. Hunting small and common things is relatively cheap - you can walk along and then do a sudden leap. Hunting bigger things is a whole lot harder - they run and you've got to catch them, then bring them to the ground and deal with a struggling animal. That is going to cost a lot more energy than hunting several small things, so if you are going for this strategy it obviously makes sense (a) to only attack if you think you've a reasonable chance of success (which is why most hunts are called off well before anything interesting happens), and (b) to target something that's going to give a really good return on your investment. In other words, once you start hunting largeish prey, it's worth going for the biggest you can possibly handle.
|Carnivore Body Mass and Energy Expenditure. Step occurs at 14.5kg. |
From Carbone et al, 2007
|They do hunt sometimes, and when they do they look mean!|
And so we come full circle: lions sleep all the time, not because they're lazy, but because hunting is such a high energy activity, that they can't afford to waste energy any other way. They don't get fat, because actually they're close to their energetic limits. It's tough being a big carnivore. (Though I still think I'd prefer it to being a wildebeest always on the look out for big carnivores!) It's interesting though - we're certainly in the large carnivore body size step, but our DEE is about 8500kJ/day in normal weight people, well below the line. We're obviously not carnivores! Though what it would be like for, say, the Hadzabe, I'm not sure - my guess is it will still be well below the line. Which isn't, to say, of course, that we can't learn from the lion's exercise regime and forget endurance-training, in favour of wildebeest wrestling. Who's first?!
Gibala, M., Little, J., MacDonald, M., & Hawley, J. (2012). Physiological adaptations to low-volume, high-intensity interval training in health and disease The Journal of Physiology DOI: 10.1113/jphysiol.2011.224725
Carbone, C., Teacher, A., & Rowcliffe, J. (2007). The Costs of Carnivory PLoS Biology, 5 (2) DOI: 10.1371/journal.pbio.0050022