AHMF: 98 Conference: Scroop

Normal Aerobic Capacity and Lactate Threshold During Incremental Exercise in Patients with CFS

G.C. Scroop, R.B. Burnet, B. Yeap, J.D. Buckley, S.S Lim and T. Ho.

Exercise Physiology Research Unit, Department of Physiology, University of Adelaide, SA 5005.

The metabolic responses during incremental exercise to exhaustion in 5 patients with Chronic Fatigue Syndrome (CFS) were compared with 5 healthy sedentary controls matched for gender (3 female, 2 male), age (CFS, 34.80 ± 4.73; controls, 35.20 ± 4.59, yr), height (CFS, 170.40 ± 4.39; controls, 171.70 ± 5.00, cm) and mass (CFS, 72.12 ± 9.58; controls, 76.58 ± 9.80, kg).

Control subjects exercised for longer (CFS, 18.80 ± 0.58; controls, 23.66 ± 1.01, min, p &LT; 0.006), reached a higher peak work load (CFS, 125.00 ± 7.91; controls, 165.00 ± 12.75, watts, p &LT; 0.04), and consequently did more work (CFS, 67.20 ± 8.78; controls, 114.45 ± 16.58, kJ, p &LT; 0.05).

Peak VO2 (VO2peak) at exhaustion was not significantly different between these 2 subject groups (CFS, 28.01 ± 1.93; controls, 35.23 ± 3.54; ml·kg-1·min-1, NS) or from their predicted VO2max determined during an earlier submaximal cycling test (CFS, 29.87 ± 1.36; controls, 33.34 ± 3.76; ml·kg-1·min-1; NS).

VO2peak was achieved at peak heart rates (HRpeak) which were not significantly different from each other (CFS, 177 ± 5; controls, 180 ± 6; beats·min-1) or from their age-predicted maximum heart rates (HRmax: CFS, 185 ± 5; controls, 185 ± 5; beats·min-1; NS).

The lactate threshold (LT, determined from a log-log plot of absolute VO2 versus blood lactate concentration) occurred at VO2 levels which were not significantly different between the 2 groups whether expressed in relative (CFS, 14.53 ± 1.26 ml·kg-1·min-1; controls 14.16 ± 2.05 ml·kg-1·min-1) or percentage (CFS, 52.2 ± 3.4; controls, 41.9 ± 7.8; % VO2peak) terms.

Despite doing less work the blood lactate concentration (CFS, 4.54 ± 0.84; controls, 6.38 ± 0.36; mmol·l-1) and VO2 at exhaustion in patients with CFS were not different from controls.

It is concluded that while the work capacity of patients with CFS is significantly less than sedentary controls, aerobic capacity and the LT are not, suggesting that factors other than so-called "deconditioning" are responsible for the earlier fatigue during exercise.