Twice at the weekend I went out running. I ran at the same time on both days and for the same distance. I slept well the night before both runs, ate similar meals, drank the same amount of liquid and felt generally fine on both days. On the first day I bounced along, running as well as I would expect. On the second day it felt like I was running through treacle; I was lethargic and it was dreadfully hard work. I haven鈥檛 subsequently gone down with any illness, so why did this happen?
鈥� I row at school, and know exactly how your correspondent feels on his runs.
What he is experiencing is the result of his previous exertions. When someone runs, rows, or does any other kind of endurance activity, lactic acid builds up in the muscles due to incomplete respiration resulting from the body鈥檚 inability to get enough oxygen to the muscles. If an individual does not warm down properly after exercise then the is not removed, leading to weakness in the muscles the following day.
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Felix Chapman, Salisbury, Wiltshire, UK
鈥� Establishing proper controls for a biology experiment is not as easy as it looks. Even using the same organism is not enough, because yesterday鈥檚 guinea pig is not today鈥檚 guinea pig, and yesterday鈥檚 runner is not today鈥檚.
For example, yesterday the runner did not have a day鈥檚 run behind him. While the body鈥檚 feedback to exercise is poorly understood, the problem does not sound like lactic acid or any obvious physiological damage. Instead, it is more probably a mental defence against unnecessary exertion.
Jon Richfield, Somerset West, South Africa
鈥� As an enthusiastic swimmer, I have kept records of the time it takes me to swim 2.5 kilometres on almost 500 occasions over the past three years. On almost all occasions I felt like I was pushing myself to within 5 per cent of my maximum ability, and a majority of the times would be within 20 seconds or so of each other. Every so often, however, maintaining the usual pace would be completely out of the question and I would end up with a time substantially slower than usual, without any obvious explanation such as poor sleeping, eating or the onset of an illness.
I noticed that there appeared to be a roughly monthly cycle, and that the poorest result often occurred a few days after a very good one. When I charted all the results together, I found that more than half of my best monthly times fell within three days of a 30-day cycle, and most of my worst monthly times fell shortly afterwards. A graph of the three years shows a repeating pattern of gradual improvement followed by a 鈥渃rash鈥� of almost 30 seconds in my time over a period of about five days. Having only noticed this pattern after most of the data had been collected, I believe I can discount any psychological effect.
鈥淭here seems to be a monthly cycle with the poorest results occurring a few days after good ones鈥�
Since discovering this I have searched unsuccessfully for an explanation, which I would anticipate is related to some fluctuation in hormones or other biorhythm. Indeed, I haven鈥檛 even been able to find an acknowledgement that this is a known effect in athletes, but I know that if I was competing at an elite level, it would be pointless to enter a competition that coincides with the worst days of my 30-day cycle. Is anyone aware of a study that examines this effect?
Ian Bradford, Flemington, Victoria, Australia