Exercise and addiction
Fun run
People, it seems, have evolved to be addicted to exercise
Apr 14th 2012 | from the print edition
AS THE legions of gym bunnies and jogging enthusiasts who race out into the spring sunshine every year clearly demonstrate, running can be fun. More specifically, running triggers the release of brain chemicals called endocannabinoids that create a potent feeling of pleasure. As their name suggests, these endocannabinoids work in the same way as the active ingredient of marijuana.
From an evolutionary standpoint this surge of endocannabinoids, and the “runner’s high” it creates, make sense. For ancient humans, remaining fit enough to run after game and away from predators and enemies was vital for survival. Yet whether other mammals are also driven to exercise by endocannabinoids has remained a mystery. Now a study led by David Raichlen of the University of Arizona has revealed that the runner’s high does exist in other species, but not in all.
Dr Raichlen hypothesised that endocannabinoid-driven exercise highs would be found in those mammals that gain an evolutionary benefit from being fast on their feet: antelopes, horses and wolves, for example. However, he also thought that they would not be present in those which are known for being quick and agile, but not for running, like ferrets. To test these ideas, he and a team of colleagues devised an experiment that monitored the endocannabinoid levels of different species after they had been walking or running on a treadmill.
The experimental animals in question were ten people, eight dogs and eight ferrets. Dr Raichlen had them run or walk on the treadmill for 30 minutes. Since running and walking speeds differ from species to species, the speed at which the treadmill moved was varied so that it raised the heart rates of the different participants to the same level. Running speeds were thus set at 2.5 metres a second for people, 1.83 for dogs and 0.84 for ferrets. Walking speeds were set at 1.25 metres a second for people and 1.1 for dogs. The ferrets proved too easily distracted to walk consistently on the treadmills and were thus left to sit quietly in their cages for this part of the study. Each participating animal ran for one session and walked for one other, and did so on separate days, to avoid exhaustion. Before and after each session, blood was drawn from each and the endocannabinoid levels in it were measured.
The researchers report in the Journal of Experimental Biology that, after 30 minutes of walking (or sitting in a cage), participants’ endocannabinoid levels did not rise. After running, however, the average human’s endocannabinoid levels rose from 2.4 picomoles per millilitre (pmol/ml) to 6.1. Dogs showed a similar trend, with levels rising from 2.4 pmol/ml to 8.0. Ferrets were different. Although they did show an increase, from 3.0 to 3.9 pmol/ml, this was not a statistically significant rise. These findings suggest that dogs experience a “runner’s high” but ferrets do not.
Dr Raichlen argues that it makes sense for ferrets not to have systems that reward cardiovascular activity, since such exercise consumes a lot of energy, may cause injury, and is not crucial to the stealthy hunting technique of sneaking down burrows and killing rabbits in their sleep. What is not clear is whether the endocannabinoid reward is an ancient mechanism that has been lost on branches of the mammalian tree that do not need it, or is something that evolves quickly in species which become active. Given that humanity’s arboreal simian ancestors would presumably have had little need to run, it is probably the latter. But to be sure Dr Raichlen will need to put animals far less co-operative than ferrets on the treadmill.
17 de abril de 2012
2 de abril de 2012
Time to be honest
..“IS SIN original?” That is the question addressed by Shaul Shalvi, a psychologist at the University of Amsterdam, in a paper just published in Psychological Science. Dr Shalvi and his colleagues, Ori Eldar and Yoella Bereby-Meyer of Ben-Gurion University in Israel, wanted to know if the impulse to cheat is something that grows or diminishes when the potential cheater has time for reflection on his actions. Is cheating, in other words, instinctive or calculating?
Appropriately, the researchers’ apparatus for their experiment was that icon of sinful activity, the gambling die. They wanted to find out whether people were more likely to lie about the result of a die roll when asked that result immediately, or when given time to think.
To carry out their experiment, Dr Shalvi, Dr Eldar and Dr Bereby-Meyer gave each of 76 volunteers a six-sided die and a cup. Participants were told that a number of them, chosen at random, would earn ten shekels (about $2.50) for each pip of the numeral they rolled on the die. They were then instructed to shake their cups, check the outcome of the rolled die and remember this roll. Next, they were asked to roll the die two more times, to satisfy themselves that it was not loaded, and, that done, to enter the result of the first roll on a computer terminal. Half of the participants were told to complete this procedure within 20 seconds while the others were given no time limit.
The researchers had no way of knowing what numbers participants actually rolled, of course. But they knew, statistically, that the average roll, if people reported honestly, should have been 3.5. This gave them a baseline from which to calculate participants’ honesty. Those forced to enter their results within 20 seconds, the researchers found, reported a mean roll of 4.6. Those who were not under any time pressure reported a mean roll of 3.9. Both groups lied, then. But those who had had more time for reflection lied less.
A second experiment confirmed this result. A different bunch of volunteers were asked to roll the die just once. Again, half were put under time pressure and, since there were no additional rolls to make, the restriction was changed from 20 seconds to eight. The others were allowed to consider the matter for as long as they wished.
In this case the first half reported an average roll of 4.4. Those given no time limit reported an average of 3.4. The second lot, in other words, actually told the truth.
The conclusion, therefore, at least in the matter of cheating at dice, is that sin is indeed original. Without time for reflection, people will default to the mode labelled “cheat”. Given such time, however, they will often do the right thing. If you want someone to be honest, then, do not press him too hard for an immediate decision.
Appropriately, the researchers’ apparatus for their experiment was that icon of sinful activity, the gambling die. They wanted to find out whether people were more likely to lie about the result of a die roll when asked that result immediately, or when given time to think.
To carry out their experiment, Dr Shalvi, Dr Eldar and Dr Bereby-Meyer gave each of 76 volunteers a six-sided die and a cup. Participants were told that a number of them, chosen at random, would earn ten shekels (about $2.50) for each pip of the numeral they rolled on the die. They were then instructed to shake their cups, check the outcome of the rolled die and remember this roll. Next, they were asked to roll the die two more times, to satisfy themselves that it was not loaded, and, that done, to enter the result of the first roll on a computer terminal. Half of the participants were told to complete this procedure within 20 seconds while the others were given no time limit.
The researchers had no way of knowing what numbers participants actually rolled, of course. But they knew, statistically, that the average roll, if people reported honestly, should have been 3.5. This gave them a baseline from which to calculate participants’ honesty. Those forced to enter their results within 20 seconds, the researchers found, reported a mean roll of 4.6. Those who were not under any time pressure reported a mean roll of 3.9. Both groups lied, then. But those who had had more time for reflection lied less.
A second experiment confirmed this result. A different bunch of volunteers were asked to roll the die just once. Again, half were put under time pressure and, since there were no additional rolls to make, the restriction was changed from 20 seconds to eight. The others were allowed to consider the matter for as long as they wished.
In this case the first half reported an average roll of 4.4. Those given no time limit reported an average of 3.4. The second lot, in other words, actually told the truth.
The conclusion, therefore, at least in the matter of cheating at dice, is that sin is indeed original. Without time for reflection, people will default to the mode labelled “cheat”. Given such time, however, they will often do the right thing. If you want someone to be honest, then, do not press him too hard for an immediate decision.
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