What causes the burning sensation in muscles during strenuous activity?

The burning sensation in muscles during strenuous activity is caused by the build-up of lactic acid.

During strenuous activity, your muscles require more energy than they can produce through aerobic respiration alone. To meet this increased demand, your muscles switch to a process called anaerobic respiration, which can produce energy without the need for oxygen. However, this process also produces a by-product known as lactic acid.

Lactic acid is a compound that your body can't use and needs to get rid of. When it builds up in your muscles, it can cause a burning sensation. This is because lactic acid is an acid, and like all acids, it can donate a hydrogen ion (H+) to other molecules. When lactic acid donates a hydrogen ion, it can disrupt the normal pH balance in your muscles, making them more acidic. This increase in acidity can irritate nerve endings in your muscles, leading to the sensation of burning.

Furthermore, the build-up of lactic acid can also interfere with the normal functioning of your muscles. This is because the increased acidity can affect the enzymes that are involved in muscle contraction, making it harder for your muscles to contract and relax as they normally would. This can lead to muscle fatigue and a decrease in performance.

In summary, the burning sensation you feel in your muscles during strenuous activity is a result of the build-up of lactic acid. This build-up can disrupt the normal pH balance in your muscles, irritate nerve endings, and interfere with muscle function.