Purpose: Increased blood lactate concentration has been suggested as a primary stimulus for the exercise-induced growth hormone response (EIGR). Patients with McArdle’s disease are unable to produce lactate in response to exercise and thus offer a unique model to assess the role of lactate in the EIGR. Accordingly, McArdle’s patients were exercised to test the hypothesis that lactate is a major stimulus of the EIGR.
Methods. Eleven patients with McArdle’s disease (3 male, 8 female; age: 35.5 ± 13.9 years, height: 166 ± 8 cm, body mass: 75.2 ± 13.1 kg) were recruited for the study. The patients walked initially at 0.42 m/s, increasing by 0.14 m/s per 3 min stage. Exercise was terminated when participants completed 3-minutes at 1.80 m/s or when a Borg CR10 pain scale rating of “4” was reached. Stages were separated by 60 s for capillary blood sampling for analysis of hGH and blood lactate concentration.
Results. McArdle’s patients’ blood lactate levels remained at resting levels (0.3 – 1.2 mM) as exercise intensity increased. Nine out of eleven participants failed to demonstrate an EIGR obtaining hGH values below the clinical definition of a response (>3 µg/L).
Conclusion. The absence of an EIGR in nine out of eleven participants suggests that lactate could play a major role in the EIGR in humans.
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