Reliability of the first ventilatory threshold assessment in people with neuromuscular diseases: Impact on exercise prescription and evaluation.

OBJECTIVE: To determine the inter-rater and test-retest reliability of the first ventilatory threshold (VT1) assessment in people with neuromuscular diseases (NMD), and its impact on exercise prescription and evaluation. DESIGN: Reliability study. SETTING: Academic hospital. PARTICIPANTS: Fifty-one ambulatory adults (mean±SD age: 63.2±10.3) with Charcot-Marie-Tooth disease (n=20), chronic idiopathic axonal polyneuropathy (n=12), post-polio syndrome (n=11), muscular dystrophy (n=6), or other NMD (n=2). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Oxygen uptake, heart rate, and workload at VT1 were assessed independently by two raters from two submaximal incremental exercise tests on a cycle ergometer, one week apart. VT1 was determined using the V-slope and ventilatory equivalents methods. Reliability was determined using intraclass correlation coefficients (ICCs) and paired t-test for systematic differences. Measurement error was expressed as standard error of measurement (SEM) or coefficient of variation (CV), and limits of agreement (LoA). RESULTS: ICCs were good to excellent for inter-rater reliability (95% confidence intervals (95%CI)=0.80-0.98), and moderate to excellent for test-retest reliability (95%CI=0.73-0.95). Inter-rater and test-retest SEM and CV ranged between 4.9% and 12.6%, with LoA ranging from 14% to 31%. CONCLUSIONS: ICCs indicated moderate to excellent reliability of VT1 assessments. Measurement errors were low at group level, with small SEM values, but higher at individual level, with wide LoA. Considering these results, VT1 can be used to detect changes in aerobic capacity in NMD at group level, but not at individual level. If VT1 is used to guide personalized exercise prescription, clinicians should anticipate that target intensity zones may be over- or underestimated in some cases, requiring close monitoring.