Lactate or lactic acid is a compound that is produced from pyruvate in a reaction that releases energy. It is also produced by bacteria and yeasts in a process called fermentation. When lactate production exceeds lactate clearance during heavy exercise, the plasma levels rise. This rise is known as the lactate threshold and is used as a measure of aerobic energy production capacity. Lactate levels can rise 10 to 20 fold during such bouts, but the increase does not cause acidification (acidosis) or the "burn." Neither does it cause the delayed onset muscle soreness that often follows such efforts.
The pH changes that accompany intense exercise are due to H ions released from ATP hydrolysis. ATP is an energy storing intermediate. The acidosis causes discomfort but it also allows easier oxygen transfer from the blood.
Lactic acid is found in many fermented (or sour) milk products such as yoghurt, kefir, and cottage cheeses. It is also found in wheat beers. It is often used as an anti-oxidant and preservative. Lactic acid can be used as fuel by muscle cells and the liver uses it as a substrate for gluconeogenesis or glucose production.
Delayed onset muscle soreness (DOMS), which occurs 24 to 72 hours after exercise is not caused by lactic acid and any lactic acid buildup quickly dissipates within minutes. The exact cause of DOMS is not known but it occurs frequently after extensive concentric contractions. It may be caused by inflammation and DOMS is often accompanied by some stiffness, swelling, and heat. Concentric contractions are contractions that shorten muscle length. It may be one of the reasons why stretching (or excentric movement) is recommended. Elongated muscle has more power and some claim stretching increases power. This is nonsense as the elongation subsides as soon as the first contraction takes place. There is no lasting elongation benefit due to stretching.
Furthermore, studies have shown that stretching has no effect on the emergence or duration of soreness. Some studies even showed that excessive stretching may cause DOMS. There is also little evidence to support the claim that DOMS promotes muscle hypertrophy as is often rumored in body building circles.
Muscle hypertrophy is most likely caused by increased glycogen storage in type IIx fibers. Since glycogen is stored inside cells with an equivalent amount of water, even small excess amounts can contribute significant bulk. Sprinters and others engaged in anaerobic activity often sport bulky muscles. The athletes may note that after extensive efforts their muscles appear somewhat "deflated."
Muscle definition is most apparent in those with little or no skin fat. That is why women almost always lack good definition, especially in their extremities. Another enhancer is dehydration and body builders often used diuretics to promote dehydration before competition.
Endurance athletes tend to be very lean and have low muscle mass. While more muscle means more power, it comes (literally) at a heavy price. The trade-off only makes sense in short events such as 100 and 200m dashes, and many swim competitions where excess weight is not an issue.
Endurance exercise on land is primarily limited by cardiac output, and excess muscle mass has a negative effect on performance. That is why weight lifting is not recommended. The increases in strength are easily offset by the excess weight. Even a little bit of extra upper body muscle can nullify a cyclist's chances at winning an event like the Tour de France, where climbing plays a significant role. Runners especially need to be very light if they are to have any likelihood of winning distance events.
Resupply (and massages)
It is often stated that endurance athletes need to resupply their bodies immediately after exercise. It is recommended that they ingest carbohydrates and protein as soon as possible to promote recovery. It has even been documented that muscle cells are more likely to pick up and store glucose in the forty minutes following intense exercise. All of this has led to many preparations and potions known as recovery drinks, recovery bars, and recovery supplements.
The reality is quite a bit different. Unless more exercise is planned in the next eight hours, there is no evidence that immediate refueling confers any advantage. It does not lead to more glycogen storage, stronger muscle, or to better and faster recovery. It does not promote faster healing if such healing is necessary (in almost all cases there is little healing to be done).
There is really no reason to expedite water or food intake. Doing so is likely to lead to excess intake in any case, as the body takes time to adjust. It is actually preferable to watch one's carbohydrate intake as it is easy to ingest 1,000 calories of carbs after intense exercise. That is way more carbohydrate than is needed. It is therefore much better to start eating normal foods as soon as possible.
There is absolutely no need for special drinks, bars or powders, even after intense long-duration exercise. Nor is there any evidence showing that such concoctions have any advantage over normal foods whatsoever.
Best is to drink some water, eat some fruit and get some rest. And a nice shower too. As for massage, be my guest. Once again there is no evidence massage promotes recovery or prevents DOMS. If excessive soreness or inflammation is present it is better to avoid massage as it may do more harm than good. Ice is the better choice in those cases.
Massages are a feel-good hug whose effect is primarily if not exclusively psychological. A gentle rub tends to alleviate pain and soreness, but has little or no effect on healing or recovery. Feel free to indulge, but don't expect any wonders here. But then again, placebo is a very strong potion so you never know!