Isoload vs isokinetic eccentric exercise: a direct comparison of exercise-induced muscle damage and repeated bout effect

摘要

Unaccustomed eccentric exercise is well-known to induce muscle damage [1-5]. The increase of muscle proteins in serum/blood, the strength decrement and muscle soreness are main indirect markers commonly used to evaluate muscle damage time-course [6]. It has been shown that exercise-induced muscle damage (EIMD) is greater after fast-velocity exercises [5] and it is dose-dependent [7]. Furthermore, EIMD is greater in young compared to old people [8] and it is higher on arms compared to legs [9]. However, a first bout of eccentric exercise confers protection against a subsequent bout of eccentric exercise, i.e., the repeated bout effect (RBE) [1, 2, 10, 11]. RBE is characterized by a faster strength recovery, a lower amount of muscle proteins in the serum and a decreased rate of soreness and swelling [12, 13]. It has been also shown that such protection lasts up to 6 months [14], and it starts after few days [15]. Interestingly, few lengthening contractions performed in the first bout are able to protect muscle from subsequent eccentric bout, in which number of repetitions is higher [7]. Even if a greater initial damage does not necessarily infers an higher protection [16, 17], when the intensity of first bout is increased, a greater adaptation occurred [11].