Feel the burn

Feel the burn is an exhortation relating to physical exercise, popularized by actress Jane Fonda in her highly successful aerobic exercise videotapes. The phrase refers to the sensation arising in a muscle being intensely exercised, which may involve a local increase in temperature but is probably due chiefly to the accumulation of metabolic products as the muscle becomes increasingly fatigued. An underlying idea is that the sensation itself provides evidence of the effectiveness of the exercise being performed. (cf. "No pain, no gain"). It probably originated with twentieth century bodybuilders, but now its use is general in exercise and sporting activities.