Glucose is the stored energy in your muscles. When training with a high intensity, your body works too hard to rely on oxygen. Glucose converts into pyruvate. Pyruvate then converts into lactate, a form of lactic acid, which produces energy but raises the acidity of the muscles.
Think of the burn you feel as you perform rep after rep. This burn interferes with tension, the main stimulus for more size and strength. Lactate forces you to stop when the contractions become too severe for your body to handle. The oxygen pathway can then take over again to produce energy that requires time at rest.
The burn you feel, and how your body adapts to it, has more to do with endurance than strength. It may feel satisfying to fight through the burn. We know though that tension is the most important factor leading to more muscle.
Lactic Acid Limits Tension
Lactic acid builds up the most during tough sets lasting 1-3 minutes. Since high rep ranges build up more lactate, low reps would seem ideal for strength and size. Low reps rely more on the ATP-CP system that generates fewer by-products of fatigue. You should fail a set because your muscle lacks the squeeze and not because they burn.
Methods that prolong a set instead of focusing on heavy weight create more lactate but fail to create much tension. This calls into question using advanced techniques to build muscle.
Some lactic acid may help though. It may boost hormones and inflammation to encourage a better rebuilding that allows more growth from the tension you do create. Some argue more lactate leads to sarcoplasmic hypertrophy but this is speculative.
For lifting, I still suggest your sets last a minute or less. Instead, address lactic acid with intervals. These raise the heart rate more so than lifting and also include the right timeframes to build up some lactate. They serve a unique purpose.
Avoid Too Much Lactic Acid
If a problem is fixable, if a situation is such that you can do something about it, then there is no need to worry. If it’s not fixable, then there is no help in worrying. There is no benefit in worrying whatsoever.
– Dalai Lama XIV
If lactic acid has a role in building muscle, you may get enough of it with intervals or through some warm-up sets and a working set of enough reps. I suggest not going too highly though and instead focusing on tension.
Consider its effect by analyzing your results. Whatever approach, either high or low reps, that allows you to add weight consistently in the long run will turn out to work best for both size and strength.
Simplify things by ignoring lactic acid and focusing on progress.