Albumin clearance from human skeletal muscle during prolonged steady-staterunning

This study was designed to find out if the lymph flow, indicated as albumin clearance, from active skeletal muscle is maintained constant during a pro longed steady-state exercise. Tc-99m-labelled albumin was injected bilatera lly into the vastus lateralis muscles of eight endurance-trained men. The r adioactivity 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 album in was calculated for each monitoring interval, and was expressed as percen tage 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 mi n 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 rapidl y to the level of 0.04 +/- 0.03% min(-1). The results showed that the album in clearance from working muscles is not constant during steady-state exerc ise, 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).