Physiological consequences of strenuous concentric and eccentric isokinetic exercises

Eccentric exercises are increasingly prescribed in the assessment and rehabilitation of musculo-skeletal injuries and disorders [1,2]. Under experimental conditions, researchers have also used isokinetic tools for investigating delayed onset muscle soreness (DOMS) induced by repeated eccentric bouts of contraction [3]. A better knowledge of the cardiovascular and metabolic response to maximal isokinetic exercise may be useful for an adequate and safe prescription of eccentric protocols. This study aimed to compare the fatigue pattern and some physiological consequences of strenuous concentric (CON) versus eccentric (ECC) isokinetic exercises. Twelve healthy male subjects (24 ± 3 years old; 70 ± 5 kg; 180 ± 6 cm) not especially trained volunteered to participate in the experimental protocol. At two different sessions separated by two weeks, subjects performed, in a randomly assigned order, either CON or ECC isokinetic contractions on a Cybex Norm dynamometer. The protocol consisted of 3 sets (separated by 30 s intervals) of 12 maximal repetitions of knee flexion (H) and extension (Q) of the dominant leg at 60◦/s. Data analysis focused in particular on the total work parameter. Metabolic (ventilation, oxygen consumption, blood lactate concentration) and cardiovascular (heart rate, mean arterial blood pressure) parameters were recorded before, throughout and after the exercise session. The total work developed during the exercise was significantly higher for the ECC compared to the CON mode. A third series / first series CON work ratio showed values of 0.72 and 0.77 respectively for the Q and H groups. The ECC fatigue ratio remained higher than 0.85, yet both muscle groups behaved differently: the ratio reached 0.95 in Q (nonsignificant decrease between third and first series) versus 0.86 in H (significant decrease between third and first series, p < 0.001). The specific fatigue pattern observed in the flexors could be hypothesized as representing a risk factor of hamstring injury. Main findings related to the physiological response consisted of (1) significantly higher heart rate after the first set of repetition in CON (176 ± 20 versus 158 ± 9 bouts in ECC), (2) two minutes after the isokinetic intervention, oxygen consumption and blood lactate concentration were significantly higher in CON. Metabolic and cardiovascular variables (ventilation, oxygen consumption, lactate and heart rate) normalized by the isokinetic total work appeared higher in CON. This study highlighted higher metabolic and cardiovascular solicitations during CON exercise compared to the ECC response. This finding should be taken into consideration when designing a strenuous isokinetic protocol.