Reliability of exhaled acetone and isoprene in healthy active adult responses to sub-maximal treadmill exercise: a pilot study

This study investigates the test–retest reliability of exhaled acetone and isoprene as potential biomarkers for monitoring exercise-induced physiological changes. Ten healthy active males (age 22.7 ± 3.7 years, height 182.4 ± 6.8 cm, body mass 80.12 ± 8.5 kg, body mass index 24.0 ± 1.4 kg/m², VO_2peak 55 ± 4 mL/kg/min, physical activity 322 min/week) provided baseline measures before undergoing a VO_2peak test and two treadmill exercise trials, interspersed by 7-days’ rest. Treadmill exercise consisted of 20 min at 80% of VO_2peak speed. Breath samples were collected before exercise, 10 min, and 24 h after exercise, using glass containers and solid-phase microextraction fibres, and analysed by gas-chromatography mass-spectrometry. Exhaled acetone exhibited poor internal consistency (Cronbach’s α = − 0.184) and agreement (ICC = − 0.096 [− 0.836–0.607], P = 0.592) with a high technical error (TE = 2.38 × 10⁶) and coefficient of variation (CV = 90%). In contrast, exhaled isoprene provided satisfactory internal consistency (Cronbach’s α 0.817) and good agreement (ICC = 0.699, P = 0.009), with a lower technical error (TE = 1.24 × 10⁶) and coefficient of variation (CV = 28%). Quadratic regression showed a decrease in isoprene 10 min after exercise during trial 1 (P < 0.01) and trial 2 (P < 0.05) and returned to baseline levels after 24 h. While acetone’s reliability was questionable, isoprene levels following 20 min of submaximal treadmill exercise are notably reproducible among healthy active males.