Anaerobic Performance Capacity in Athletes

Anaerobic performance characteristics of the whole body and at muscle tissue level were studied in 89 athletes and 31 reference subjects. The main parameters were vertical velocity during running up the stairs, maximal isometric force of leg extensor muscles, blood lactate concentration after maximal treadmill running test, percentage of fast twitch muscle fibers (% FT fibers), lactate dehydrogenase (LDH) and creatine phosphokinase (CPK) activity in vastus lateralis muscle. These parameters tended to divide the athletes and their sport events into neuromuscular, anaerobic and aerobic types. The specific needs of the different sport events might have masked the expected characteristics of energy and power utilization. However, a high percentage of FT fibers might be a prerequisite for a successful athlete in certain neuromuscular-anaerobic type events (“power events”). The main parameters describing the anaerobic performance capacity of the whole body (vertical velocity, leg force, blood lactate) were found to be related to muscle fiber composition (% FT fibers). The running velocity rather than muscle strength seemed to be more influenced by activity of enzymes LDH and CPK.     

Nonsteroidal anti-estrogens inhibit the functional differentiation of human monocyte-derived dendritic cells

Dendritic cells (DC) are professional antigen-presenting cells with a unique capacity to initiate and regulate immune responses. Immature CD1a(+) DC can be cultured from CD14(+) monocytes in the presence of interleukin (IL)-4 and granulocyte macrophage colony-stimulating factor in vitro. Results of this study show that the nonsteroidal anti-estrogens toremifene and tamoxifen inhibit this differentiation. In the presence of anti-estrogens the cells lose CD14 expression, but remain CD1a(-) and clearly have less dendritic processes than immature DC. Functionally, anti-estrogen-treated cells are inferior to immature DC in inducing proliferation of allogeneic T cells and in producing IL-12 p70 protein after CD40 ligation. The expression of the costimulatory molecules CD80 and CD86 is differentially regulated by anti-estrogens during DC differentiation. Furthermore, anti-estrogens are also able to inhibit the terminal maturation of DC. By inhibiting the functional differentiation of DC, anti-estrogens may have a role in the treatment and prevention of autoimmune diseases. (Blood. 2000;95:2875-2882)     

Leg stiffness modulation during exhaustive stretch-shortening cycle exercise

The present study examined the effects of muscle activity modulation on leg stiffness during an exhaustive stretch-shortening cycle (SSC) exercise in eight male subjects. Reaction force, electromyography (EMG) of the soleus (Sol), gastrocnemius (Ga) and vastus lateralis (VL) muscles and sledge seat position were recorded during the SSC exercise, consisting of 100 maximal intermittent drop jumps followed by a continuous submaximal jumping until exhaustion, on a sledge apparatus. Metabolic loading was determined by measuring blood lactate (La). No change was found in leg stiffness during the maximal jumps, whereas the subsequent submaximal jumping induced a significant reduction by 27+/-12% (P<0.05). Leg stiffness was closely related to the EMG ratio between the braking and push-off phases in Sol (r=0.81, P<0.05) and particularly in Ga (r=0.98, P<0.001) (but not in VL, r=0.64, NS) at the end of the submaximal jumping. Furthermore, the post-exercise La was significantly associated with the EMG ratio at the end of the submaximal jumping in Sol (r=-0.88, P<0.01) and Ga (r=-0.98, P<0.001). These results indicate that activity modulation between the braking and push-off phases in the triceps surae muscle, particularly in Ga, plays an important role in leg stiffness adjustments during fatiguing SSC exercise. It is suggested that efficient activity modulation (i.e. high EMG ratio) of the triceps surae muscle during an intensive fatiguing SSC exercise may postpone the exhaustion and development of metabolic fatigue.     

Medial gastrocnemius muscle behavior during human running and walking

Utilization of elastic energy in the tendinous tissues (TT) of the human skeletal muscle may be task dependent. The present study was designed to investigate this problem by comparing the fascicle-TT interaction of the medial gastrocnemius muscle (MG) during ground contact of running and walking. Seven subjects ran and walked with a natural cadence. Ankle and knee joint angular data were recorded by electrogoniometers for estimating the entire MG muscle-tendon unit (MTU) length, together with the ground reaction forces. The MG fascicle length was measured by using the high-speed ultrasound image scanning during movements. The results showed that in running, after the rapid early fascicle stretching (0-10% of the contact period), the fascicles shortened throughout the ground contact while TT was stretched prior to shortening. In walking, the fascicles shortened initially (0-15% of the contact period) due to sudden plantar-flexion. Thereafter, the fascicles and TT lengthened slowly until the end of single support (15-70% of the contact period.). The fascicles then shorted during the push-off phase (70-100% of the contact period). These results demonstrate that the MG fascicles behaved differently between running and walking and did not follow the length change pattern of the MTU during the ground contact period. The estimated working range of active muscle fibers in force-length relationship could shift more to an ascending limb (shorter length) phase in running than in walking. These results suggest that MG fascicles can work within the optimal working range of the sarcomeres in the force-length relation but are responsible for the effective utilization of the TT elasticity during human running.     

Excitability of the soleus reflex arc during intensive stretch–shortening cycle exercise in two power-trained athlete groups

In several explosive types of sport events the leg extensor muscles are subjected to very high impact loads. Thus, extreme requirements exist for the neuromuscular system to develop sufficient muscle stiffness in the lower extremities in order to tolerate these high impact loads. Therefore, it would be challenging to measure reflex modulation during high impact activities, and with different athlete populations. In the present experiment, H-reflex and short latency reflex (M1) sensitivity was measured during drop jump exercises among high jumpers and sprinters. The changes in both reflex peak-to-peak amplitudes showed a significant (P < 0.05) reduction towards the end of the exercise for the sprinters. In addition, the same subject group showed a remarkable increase in serum creatine kinase (CK) activity 2 h after the jumps. Similar changes could not be observed for the high jumpers. These results clearly indicate different neural adaptation strategies for the two athlete groups. Reduction in H-reflex sensitivity and an increase in CK-activity in sprinters were taken as evidence for presynaptic inhibition, probably induced by substances related to muscle damage. Since high jump training includes more high impact loading, it was assumed that it could lead to some structural adaptation and, thus, prevents exercise induced reflex modification to a certain extent.     

Maximal force during eccentric and isometric actions at different elbow angles

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80° or 110° and ending at 140° elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10° of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80° and in 110° starting position at all three velocities (1, 2, and 4 rad s⁻¹). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10° of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.     

Effects of exhaustive stretch-shortening cycle exercise on muscle blood flow during exercise

Aim: The influence of exhaustive stretch‐shortening cycle exercise (SSC) on skeletal muscle blood flow (BF) during exercise is currently unknown. Methods: Quadriceps femoris (QF) BF was measured in eight healthy men using positron emission tomography before and 3 days after exhaustive SSC exercise. The SSC protocol consisted of maximal and submaximal drop jumps with one leg. Needle biopsies of the vastus lateralis muscles were taken immediately and 2 days after SSC for muscle endothelial nitric oxide synthase (eNOS) and interleukin‐1‐beta (IL‐1β) mRNA level determinations. Results: All subjects reported subjective muscle soreness after SSC (P < 0.001), which was well in line with a decrease in maximal isometric contraction force (MVC) and increase in serum creatine kinase activity (CK) (P = 0.018). After SSC muscle BF was 25% higher in entire QF (P = 0.043) and in its deep and superficial muscle regions, whereas oxygen uptake remained unchanged (P = 0.893). Muscle biopsies revealed increased IL‐1β (30 min: 152 ± 75%, P = 0.012 and 2 days: 108 ± 203%, P = 0.036) but decreased or unchanged eNOS (30 min; ?21 ± 57%, P = 0.050 and 2 days: +101 ± 204%, P = 0.779) mRNA levels after SSC. Conclusion: It was concluded that fatiguing SSC exercise induces increased muscle BF during exercise, which is likely to be associated with pro‐inflammatory processes in the exercised muscle.     

Surgical hypothermia in a patient with a cold agglutinin. Management by plasma exchange

Cold agglutinins are a potential danger to patients who must be subjected to hypothermia. A patient with a cold agglutinin of moderate titer but broad thermal amplitude was to undergo hypothermia during aortic valve replacement. He was managed preoperatively with an eight- liter plasma exchange by continuous-flow centrifugation to remove the cold agglutinin. There were no adverse effects during or after hypothermia.