Skeletal muscle force generating capacity following recovery from bouts of high intensity endurance training

INTRODUCTION The literature concerning recovery from endurance training and its effects on performance of isotonic and isokinetic contractions is limited. It has been demonstrated that maximal isokinetic torque is reduced following a cross country skiing race (3). A reduction in maximal isometric and concentric force has also been shown following performance of a submaximal bicycle test to exhaustion (5). Further, reductions in maximal voluntary contraction following exhaustive dynamic exercise have been demonstrated (5). It has also been reported that strength enhancement is related to the amount of tension that can be developed in the contracting muscle during resistance training (1). Therefore, performance of bouts of strength training without subsequent recovery from endurance training may have a detrimental effect on strength development. The purpose of this study was to quantify the ability of skeletal muscle to generate maximal force following a bout of high intensity cycling exercise and subsequent recovery. In an effort to mimic training conditions encountered by cyclists, both submaximal and supramaximal cycling was incorporated into the endurance training session. METHODS Fourteen males, aged 18-30 years, who had a minimum of 12 months cycling experience participated as subjects. Each subject was assessed for maximal oxygen consumption (VO2max) during a continuous incremental cycle test to exhaustion on a cycle ergometer (Monark, Sweden). Lower limb muscle strength and power tests were administered before as well as 6, 24 and 48 hours after a session of high intensity cycle exercise. Strength and power of the lower limbs were measured by (i) maximal isokinetic leg extensions performed at slow (60deg/s), medium (120deg/s) and fast (180deg/s) speeds on a Cybex II ergometer, and (ii) concentric isoinertial squat jumps using a plyometric power system (Plyopower Technologies, Lismore, Australia) in which maximum force and rate of force development (RFD) were determined. The high intensity exercise involved each subject cycling for 30 minutes at a workload corresponding to their lactate threshold which was determined by the Dmax method (2). Following 10 minutes of recovery, subjects performed 4 bouts of supramaximal cycling for 1 minute, with 1 minute rest, at a workload corresponding to 120% of VO2max. Following this exercise, subjects were re-tested for strength and power after a period of passive rest of either 6, 24 or 48 hours. Each subject was tested in all of designated recovery periods so that the cycling exercise followed by the strength testing session were performed on three separate days. RESULTS A significant (p\u3c0.05) reduction was found for maximal isokinetic peak torque performed at the slow speed contraction following 6 hours of recovery from the cycling exercise (Mean+/-SD, 225+/-34 vs 199+/-27 Nm). A nominal reduction in peak torque was also found for contractions performed at medium (178+/-23 vs 173+/-23 Nm) and fast (151+/-27 vs 145+/-25 Nm) fast speeds, however, these were not significant (p\u3e0.05). No significant (p\u3e0.05) differences were found for fast, medium or slow isokinetic contractions performed prior to the cycle exercise and at 24 or 48 hours of recovery. Although, there was a trend for maximum force (1381+/-172 vs 1313+/-214 N/s) and RFD (9116+/-2342 vs 8632+/-2540 N/s) during the concentric squat jumps to be reduced at 6 hours of recovery, these were not significant. No significant differences were found at 24 or 48 hours of recovery for maximum force and RFD during the concentric squats jumps. DISCUSSION AND CONCLUSION The results of this study have shown that strength and power performance of the lower limbs are reduced following the cycle endurance exercise. At 6 hours post exercise there was a reduction in isokinetic and isoinertial force generating capacity. However, by 24 hours these reductions had returned to the resting levels. These results support earlier research concerning recovery of maximal voluntary contractions following exhaustive dynamic exercise (4). The reduction in force generating capacity shown in this study also highlights the potential for strength gains to be inhibited if resistance training is performed without sufficient recovery from endurance exercise. These results have practical applications for athletes who are combining both resistance and endurance elements in their overall training regime. REFERENCES (1) Atha J. (1981). Exer. Sport Sci. Rev. 9: 1-74. (2) Cheng B., Kuipers H., Snyder A.C., Keizer H.A., Jeukendrup A. & Hesselink M. (1992). Int. J. Sports Med. 13: 518-522. (3) Frosberg A., Tesch P. & Karlsson J. (1978). In Biomechanics VI-A, Asmussen E. & Jorgensen K.(ed.). (4) Kroon G.W. & Naeije M. (1988). Eur. J. Appl. Physiol. 58: 228-232. (5) Sahlin K. & Seger J.Y. (1995). Eur. J. Appl. Physiol. 71: 180-186