Myofibrillar disruption following acute concentric and eccentric resistance exercise in strength-trained men

We have previously quantified the extent of myofibrillar disruption which o ccurs following an acute bout of resistance exercise in untrained men, howe ver the response of well-trained subjects is not known. We therefore recrui ted six strength-trained men, who ceased training for 5 days and then perfo rmed 8 sets of 8 uni-lateral repetitions, using a load equivalent to 80% of their concentric (Con) 1-repetition maximum. One arm performed only Con ac tions by lifting the weight and the other arm performed only eccentric acti ons (Ecc) by lowering it. Needle biopsy samples were obtained from biceps b rachii of each arm similar to 21 h following exercise, and at baseline (i.e ., after 5 days without training), and subsequently analyzed using electron microscopy to quantify myofibrillar disruption. A greater (P less than or equal to 0.05) proportion of disrupted fibres was found in the Ecc arm (45 +/- 11%) compared with baseline values (4 +/- 2%), whereas fibre disruption in the Con arm (27 +/- 4%) was not different (P > 0.05) from baseline valu es. The proportion of disrupted fibres and the magnitude of disruption (qua ntified by sarcomere counting) was considerably less severe than previously observed in untrained subjects after an identical exercise bout. Mixed mus cle protein synthesis, assessed from similar to 21-29 h post-exercise, was not different between the Con- and Ecc-exercised arms. We conclude that the Ecc phase of resistance exercise is most disruptive to skeletal muscle and that training attenuates the severity of this effect. Moreover, it appears that fibre disruption induced by habitual weightlifting exercise is essent ially repaired after 5 days of inactivity in trained men.