So we've all heard the painful stories behind the so-called 'lactic acid build up' after a tough workout. But how true is that statement? To be honest, lactic acid does not cause muscle soreness and it’s not the sole reason behind the burning in your muscles either. Lactic is a real thing but it doesn’t stick around long once your body gets enough oxygen again to do its thang... Meaning the build up doesn’t last for days and it’s not the reason your muscles are sore the following day after a workout.
Soreness is due to molecular energy break down (creating an acidic environment) and small tears in the muscle fibers. If the body cannot recover well, get rid of the byproducts from the energy breakdown, and repair the muscle tears, then the soreness and muscle pain lasts longer.
Lemme break this down... During anaerobic activities (think weight lifting or HIIT training) when oxygen demand becomes higher than actual oxygen supply, our bodies have to supply us energy WITHOUT sufficient amounts of oxygen.
Without oxygen, glucose molecules end up being converted into lactic acid instead of traveling down its preferred energy pathway (usually glucose would ultimately provide us with energy as ATP when oxygen is present, which is called aerobic metabolism). Lactic acid can 'build up' in the blood causing you to experience muscle soreness and burning, nausea and rapid breathing (because the body wants oxygen to rid the lactate build up) think about how you feel after one intense HIIT interval... gassed right? But as I said earlier, it doesn't stick around long enough to blame it for your muscle soreness.
The picture below illustrates how glucose (our main energy substrate) is released from the liver into the blood where its taken to the muscle during a workout. Glucose can be used immediately or stored glycogen (stored energy) can be released from the muscles for energy use.
Without enough oxygen, the final substrate in the energy production pathway, pyruvic acid, is converted into lactic acid. It can hang around in the muscles which is why people can experience muscle pain.
SO HOW DO WE GET RID OF THIS? Well... TIME! Lactate is usually cleared from the body in 30-60 minutes, it does not 'build up.' It's quickly released into the blood, taken up by the liver and recycled and reused to make pyruvic acid and glucose again. This process is part of the gluconeogenic pathway which creates new glucose from non-carbohydrate substrates to provide the body and muscles with energy. This process is actually 'inefficient' meaning it uses more energy than it creates, but it's a necessary process to get rid of the lactate and provide the body with its primary form of fuel, glucose. After your workout, the body gets back enough oxygen and is in an aerobic/oxygen rich state again. The new glucose produced from lactic acid can be converted into usable energy! Yay fuel!
Takeaway message: Tell all your friends that 'lactic acid build up' is technically a myth!
Post workout recovery is still good to do for general muscle soreness and a quality post-workout meal, one balanced in protein, carbs and little fat, can also be beneficial for recovery. The more you know, the more empowered you can feel!