In the concentric exercise form, there was a mean contraction rate of 40·min-1 and in the eccentric mode of 17·min-1 for the knee, 67·min-1, and 40·min-1 for the ankle joint, respectively. Due to the higher maximum work in the eccentric mode (384 J/repetition vs 156 J/repetition), there was no difference in total work during an exercise time of 1 min between concentric (6240 J) and eccentric forms (6528 J) of exercise for the knee (NS). For the ankle joint, the work per repetition was 48 J and 93 J in concentric and eccentric mode; no difference occurred in total work (3216 J and 3720 J, NS).
The FI showed clearly lower values in concentric exercise compared with eccentric exercise in both joints (P < 0.001;Fig. 3). There was no difference between flexion and extension in the knee (NS); in the ankle, the FI for dorsiflexion was 26% below that of plantarflexion (P < 0.01). In the eccentric mode, the greatest fatigue was seen in dorsiflexion. The least concentric fatigue was found in plantarflexion, which means that the FI for concentric and eccentric differs least (quotient eccentric/concentric 1.47 ± 0.48). The greatest difference was found in dorsiflexion (2.32 ± 0.98), followed by knee extensors and flexors with 1.83 ± 0.48 and 1.65 ± 0.40.
With age, the FI in the concentric forms of exercise in the knee joint showed a slight increase (lower fatigue) between 8 and 16%, in eccentric forms between 2 and 8%. In the ankle musculature, pronounced fatigue between 13 and 30% was seen in the concentric mode, and between 0 and 10% in the eccentric mode.
The metabolic reaction for lactate in the individual muscle groups is shown in Figure 4 as the difference from baseline to maximum value. The lactate concentrations increased in all exercises to a highly significant degree above the resting value. At the same time, the increase was significantly higher in all concentric exercises than in the eccentric exercises. The thigh musculature in the concentric mode reached more than the four-fold; the ankle musculature tripled the values compared with the eccentric mode.
Starting with a resting value of 2.0–2.2 mmol·L-1, the increase in the concentric for the knee joint reached nearly double that of the ankle, in the eccentric the low increases were of the same magnitude. The maximum increases after concentric exercise occurred in the knee joint in 39% of the subjects after 3 min and in 56% after 5 min. In the ankle, the distribution is 70% to 23%. After eccentric exercise, the maxima for both joints were found in 33% immediately, 3 min, and 5 min after the end of exercise.
The correlations between lactate differences and the FI showed a significant relationship only for the knee. For flexion in the concentric mode (r = −0.41, P < 0.001), no significant relationships were observed for any other forms of exercise.
The behavior of the ammonia concentrations before and after exercise were comparable to the lactate concentrations (Fig. 5). For the knee extension in concentric mode, there was a correlation to the FI of r = −0.29 (P < 0.05), for the knee flexion of r = −0.35 (P < 0.01). There was no significant relationship for the eccentric forms of exercise in the knee or any ankle exercises.
Between lactate and ammonia values in the concentric mode, there was a correlation of r = 0.58 for the knee and r = 0.55 for the ankle (P < 0.001). In the eccentric mode, the values were not significant.
In many sports disciplines general and sport-specific strength training or strength-endurance training plays an important role. The effect of training depends in part from the tension attained and the number of times the stress is repeated. From this point of view, eccentric forms of exercise are interesting, because usually greater strength and tension values are attained than in concentric or isometric forms. It is unclear whether this is accompanied by elevated metabolic stress to the exercised musculature.
To investigate this, the total work performed in concentric and eccentric exercise mode were kept comparable by selecting a higher angular velocity for the concentric mode. This did increase the difference in average torque between the eccentric and concentric exercise somewhat, but the main difference is most likely due to an elementary characteristic, seen as variable visco-elastic properties of the muscle fiber (11). This assumption is supported by evidence of lower neuromuscular activity in spite of greater strength development in the eccentric mode than in concentric forms of exercise (14,25). The findings reported by Aratow et al. (1) in the musculus soleus and musculus tibialis anterior may also be interpreted in this way, in which further eccentric tension development was demonstrated in spite of maximum nerve innervation. This difference can be seen in this study in both the knee joint and ankle, even though the difference in the knee was somewhat lower than in the ankle. Apparently, the thigh musculature attains a somewhat higher proportion of maximum strength than the calf musculature at the selected angular velocity in the concentric mode (180°·s-1).
The known decrease in maximum strength was observed during concentric endurance exercise over 1 min (4,13,16,20,21,22). The values for extension are somewhat higher and of the same magnitude for flexion (9). Although greater fatigue is found in isometric and concentric exercise in endurance exercise, the higher the maximum applicable strength is (7), the lower fatigue is as described by Gray and Chandler (10) and by Verdonck et al. (24) in eccentric than in concentric endurance exercise. This agrees with the data we recorded, which demonstrated lower fatigue (higher FI) in eccentric forms of exercise.
The metabolic reaction findings support the assumption that the factors which result in muscular fatigue in concentric exercise play a lesser role in eccentric endurance exercise (22). Considerably greater increases are observed in both lactate production and ammonium production in the concentric mode than in the eccentric mode. The behavior of the metabolic reaction is joint-independent and differs only in the absolute values due to lower muscle mass used in the ankle. The mean contraction rate in the concentric mode of about 40 movements·min-1 for the knee and 67 for the ankle is about twice as great as in the eccentric mode (17·min-1 and 40·min-1), but the strengths and tensions attained in the eccentric mode are much higher and should theoretically lead to greater metabolic answer of lactate and ammonia than the concentric exercise.
Our results thus agree with the findings of Bonde-Petersen et al. (3) and Knuttgen (14), who also demonstrated very low lactate values after eccentric stress compared with concentric forms of exercise. Earlier studies did not find this difference, but no comparative methodology was applied (15).
The ammonia reaction was qualitatively comparable to lactate. Because the purine-nuclide cycle is greater in FT fibers than in ST fibers (6,12,23), and thus affected by higher strength and tension stresses, this may be taken as further evidence that there is a basically different form of stress between concentric and eccentric exercise (17,18). This is also supported by a correlation between the increases in the metabolites lactate and ammonia to fatigue which can only be established in concentric forms of exercise, a finding that agrees with the report by Douris (5).
The present study thus generally supports the assumption that the elevated strength and tension values at comparable work level in the eccentric mode result in lower metabolic stress than in the concentric mode. This agrees with the supposition that these greater strengths and tensions are located in the actin-myosin structure via additive, passive elastic strengths at the molecular level. It remains uncertain whether the lower metabolic stress might be useful during the training process. A greater scope of training and increased number of training stimuli might be applied in primarily eccentric forms of exercise. Additional training studies are needed for substantiation of this hypothesis relevant for training practice.
Address for correspondence: PD Dr. med. Thomas Horstmann, Medical Clinic and Policlinic, University of Tübingen, Department of Sports Medicine, Hoelderlinstr. 11, D- 72074 Tübingen, Germany; E-mail: email@example.com.
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Keywords:© 2001 Lippincott Williams & Wilkins, Inc.
LACTATE,; AMMONIA,; MUSCULAR FATIGUE