Lactic acid is a by product of muscle contractions and in excess can cause soreness. Muscle cramps are from involuntary muscle contractions. I asked earlier if magnesium was in your sport drink because magnesium is a muscle relaxer and calcium is a muscle contractor. Sweating and excessive urinating can deplete your magnesium and you store very little, unlike calcium which you have great stores in bone. Magnesium can also be leached from your body by coffee, caffeine, sugar, alcohol. The best way to absorb it is with a 2:1 ratio of calcium to magnesium, that why they added the calcium to the sport drink. Sources of magnesium are raw almonds and green leafy veggies to name a few. Take a magnesium supplement in the form that is chelated to amino acids so it can ride piggyback on the amino acid and get across the cell membrane efficiently. It works great for cramps and relaxes your body for better sleep too.