Albumin clearance from human skeletal muscle during prolonged steady-state running.

This study was designed to find out if the lymph flow, indicated as albumin clearance, from active skeletal muscle is maintained constant during a prolonged steady-state exercise. 99mTc-labelled albumin was injected bilaterally into the vastus lateralis muscles of eight endurance-trained men. The radioactivity at the injection site was monitored by a gamma-camera before, frequently during, and after a 2 h run at a controlled steady intensity of 69 +/- 4% of the maximal heart rate. The fractional clearance rate of albumin was calculated for each monitoring interval, and was expressed as percentage clearance per minute (% min(-1)). During the first 15 min of exercise the clearance rate was five times higher than at rest before the exercise (0.29 +/- 0.12 vs. 0.06 +/- 0.05% min(-1), P = 0.001). During the next 25 min of running the clearance rate fell to 0.19 +/- 0.08% min(-1) (P = 0.02), from which level it was further attenuated, being 0.12 +/- 0.04% min(-1) at the end of the exercise. After the exercise the clearance rate fell rapidly to the level of 0.04 +/- 0.03% min(-1). The results showed that the albumin clearance from working muscles is not constant during steady-state exercise, suggesting that lymph flow from exercising skeletal muscle may not be constant despite lymphatic pumping being assumed to be unchanged during the course of exercise (i.e. constant exercise intensity and running speed).

Lymph flow dynamics in exercising human skeletal muscle as detected by scintography.

1. The effects of dynamic and isometric muscle contractions on the lymph flow dynamics in human skeletal muscle were studied with a scintographic method. 2. Radioactively labelled human serum albumin (99mTc-HSA) was injected bilaterally into the vastus lateralis muscles of eight men (n = 16), four of whom had had an endurance training background. The subjects performed 100 submaximal contractions in 10 min as (i) dynamic knee extensions (CONS), (ii) isometric contractions with the knees at full extension (IMExt), or (iii) isometric contractions with knees fixed at 90 deg angle flexion (IMFlex). The exercises were separated by 65 min periods in supine rest. The level of radioactivity at the injection site was monitored by a gamma-camera, and the clearance rate of radioactivity (CR) was calculated as the fractional decrease during the periods of interest (CR unit = % min-1). 3. The clearance rate was low during the rest periods (0.04 +/- 0.05% min-1), though higher in the trained than in the sedentary subjects (0.06 +/- 0.05 vs. 0.03 +/- 0.03% min-1; P = 0.008). Exercise increased the clearance rate three- to sixfold, to 0.16 +/- 0.16% min-1 during CONS, 0.20 +/- 0.15% min-1 during IMExt and 0.09 +/- 0.11% min-1 during IMFlex. There were no differences between the subject subgroups. 4. The higher clearance rate during IMExt than during IMFlex (P = 0.02) demonstrates the importance of muscle deformations on lymph propulsion and experimentally confirms the current concepts of lymph formation and propulsion in voluntarily active skeletal muscle. It is suggested that lymph propulsion by working muscle is most efficient when the muscle is able to shorten close to its minimum length.

Exercise-induced increase in serum creatine kinase is modified by subsequent bed rest.

This study was designed to find out if bed rest, which is known to markedly reduce peripheral lymph flow, immediately after strenuous exercise could affect the behaviour of creatine kinase activity (CK) in serum. Eleven endurance athletes performed an 18 km cross-country run, after which six of the subjects were placed in bed rest group (BR) for 23 hours, while a group of five control subjects maintained their normal habitual activity (C). After the bed rest all subjects performed a light jogging bout for 45 min. Seven hours after the exercise serum CK was increased threefold (p < 0.05) in both groups. During the next 16 hours serum CK increased further 30% in C (p < 0.05) but decreased (p < 0.05) in a similar magnitude in BR. Light jogging elicited a transient CK increase of 16% (p < 0.05) in C, but there was no change in BR. The fact that serum CK increased similarly in both groups during the first hours after the exercise shows that the transport of CK from muscles into circulation can be maintained for some hours despite absence of muscular activity. However, the later post-exercise serum CK response may be diminished by bed rest (effect of posture and/or lack of muscle function). The reduced response is also seen in the CK response to a repeated exercise. These observations suggest that a short-term physical inactivity (bed rest) may reduce both the lymphatic transport of CK and the release of enzyme from muscle fibres.

Orienteering performance and ingestion of glucose and glucose polymers.

The benefit of glucose polymer ingestion in addition to 2.5 per cent glucose before and during a prolonged orienteering competition was studied. The final time in the competition in the group ingesting 2.5 per cent glucose (group G, n = 10) was 113 min 37 s +/- 8 min 11 s, and in the group which had additionally ingested glucose polymer (group G + GP, n = 8) 107 min 18s +/- 4 min 41 s (NS). One fifth (21 per cent) of the time difference between the two groups was due to difference in orienteering errors. Group G + GP orienteered the last third of the competition faster than group G (p less than 0.05). The time ratio between the last third of the competition and the first third of the competition was lower in group G + GP than in group G (p less than 0.05). After the competition, there was statistically insignificant tendency to higher serum glucose and lower serum free fatty acid concentrations in group G + GP, and serum insulin concentration was higher in group G + GP than in group G (p less than 0.05). Three subjects reported that they exhausted during the competition. These same three subjects had the lowest serum glucose concentrations after the competition (2.9 mmol.1(-1), 2.9 mmol.1(-1), 3.5 mmol.1(-1] and all of them were from group G. It is concluded that glucose polymer syrup ingestion is beneficial for prolonged psychophysical performance.

Mechanical jumping power in young athletes.

Mechanical jumping power was determined for 286 young male athletes representing six sports events and ranging in calendar and skeletal ages from 8.8 to 17.1 and from 7.8 to 18.1 years, respectively. The subjects performed successive maximal vertical jumps on a contact mat for 30 s. The number of jumps and their cumulative flight time after 15 and 30 s were used for calculations of mechanical power. The jumping performances of the young athletes were found to be reproducible from the age of 10-12 years in respect to the angular displacement of the knee and duration of contact. Absolute mechanical power, as well as power related to body weight, increased with calendar and skeletal ages. Of the anthropometric characteristics, the circumference of the thigh and body weight showed the highest correlation with mechanical power; subjects with the greatest thigh circumference and body weight having the lowest mechanical power. The subjects were divided into 'power' (track and field, gymnastics) and 'endurance' (skiing, orienteering) groups. The former reached higher mechanical power values than the latter. Mechanical power for the second 15-s jumping period was on average 4.7% lower than for the first. The events did not differ from each other in respect of the decrease in power.