For over ten years I have used a little known technique called buffering to improve my race times. Buffering relieves the pain of lactic acid in my muscles during the last fifty of the 200 breaststroke and butterfly events. The reason why your arms and legs burn and fail to respond properly is that your blood pH gets too acidic, this due to anaerobic swimming during the race. The day of your race you should never consume acidic drinks such as colas, orange juice, etc., that when absorbed would lower the blood pH.
I then use flavored TUMS to not only calm my upset stomach, but to buffer the acid formed in my muscles during my races. Many studies have been made on runners, swimmers, and cyclists using sodium bicarbonate to buffer the blood. All the studies have come to the same conclusions that improvements in performance occur between 30 seconds to three minutes. This happens to fall in the range of my 50, 100, and 200 Breaststroke races. Unfortunately the sodium bicarbonate sometimes causes severe gastric distress, from belching to stomach bloating. The East Germans used this for their swimmers who could tolerate it.
I have found that TUMS (calcium carbonate) works almost as well, without the gastric problems. I start taking the first of the 40 TUMS about 90 minutes before important 200 Breast races, finishing up the last ones 20 minutes before the race. Of course I drink lots of water to hydrate myself while taking the tums. When I use TUMS, at the end of the race my arms and legs do not have the pain from lactic acid nearly as much. There is usually at least one to two seconds' improvements in my race times. This is consistent with the values in the research studies.
I would recommend taking three TUMS 25-35 minutes before a race to see how your body responds, then working upwards from there. The studies recommend 180mg of calcium carbonate per pound of body weight. Each TUMS contains 500mg of carbonate. Therefore a 100 pound woman should take 36 TUMS and a 150 pound man would take 54 TUMS. I weigh 190 pounds and found 40 TUMS works for me. You can start at a mid level and work up from there. After a hard workout that produces a lot of lactic acid (either weights or swimming), take 1-3 TUMS and you will be not as sore the next day. In addition each TUMS contains 200mg of Calcium, something both men and women need as we get older to prevent osteoporosis.