Strenuous eccentric exercise has been shown to cause a decrease in maximum voluntary contraction (MVC) that persists for several days after exercise, and is more pronounced when measurements are performed at short muscle lengths (Saxton & Donnelly, 1996). A previous paper by Jones et al. (1989) reported that a decrease in force may also occur after maximal isometric exercise when the contracting muscles are fixed at a long muscle length. The purpose of the present study was twofold: (1) to examine whether a protocol of repeated maximal isometric contractions at long muscle length causes long-term decreases in MVC, and (2) to observe whether the magnitude of decrease in MVC following this type of exercise is dependent on muscle length.

Seven male volunteers (age 26.6 ± 2.2 years, height 174.7 ± 1.8 cm, mass 74.3 ± 4.3 kg, means ± S.E.M.) participated in the study that had been approved by the University Committee. Following familiarization, the MVC of the elbow flexors was measured at five different elbow angles: 50, 70, 90, 140 and 160 deg. Three days after the preliminary force measurements, each subject performed 50 maximal voluntary isometric muscle contractions (10 s contraction-20 s rest) of the elbow flexors with the shoulder hyper-extended at 45 deg and the elbow joint fixed at 140 deg. This position was chosen to make the elbow flexors to contract from a lengthened position. Following the exercise protocol the MVC at the above five elbow angles, range of motion (ROM), muscle soreness and plasma creatine kinase activity were measured at 24 h intervals for 4 days. Statistical analyses were performed using a two-way analysis of variance.

The greatest decrease (about 40 %) in MVC, 24 h after isometric exercise, was observed at the more acute elbow angles (50 and 70 deg, P < 0.01, Fig. 1). On the same day, smaller decreases of 26 and 16 % in MVC were found at the elbow angles of 90 and 140 deg (P < 0.01), while no significant decrease in MVC was evident at the elbow angle of 160 deg (Fig. 1). MVC restoration was a function of the elbow angle, with force recovery being less at the smaller angles throughout the 4-day observation period (Fig. 1). This pattern of angle-specific MVC decline may be attributed either to sarcomere overstretching, which caused a subtle increase in muscle length and therefore a shift in the force-length relationship, or to a differential activation of the contracting muscles.