Test-Retest Reliability of Critical Power, Critical Heart Rate, Time to Exhaustion, and Average Heart Rate during Cycle Ergometry

Succi PJ, Dinyer TK, Byrd MT, Soucie EP, Voskuil CC, Bergstrom HC. Test-Retest Reliability of Critical Power, Critical Heart Rate, Time to Exhaustion, and Average Heart Rate during Cycle Ergometry. JEPonline 2021;24(2):33-51. This study examined the test-retest reliability of the determination of critical power (CP), critical heart rate (CHR), time to exhaustion (T_Lim), and average heart rate (HR_avg). Ten moderately trained subjects (mean ± SD, age 22.8 ± 3.5 yrs) completed a graded exercise test to exhaustion to determine VO_2peak and the power output associated with VO_2peak (pVO_2peak). The CP and CHR were determined from two individual sets of 4 trials to exhaustion at 85%, 90%, 95%, 100% pVO_2peak (P₁-P₄) with TLim and HRavg recorded. Separate one-way repeated-measures ANOVAs (P<0.05) were used to compare the means between the tests and the reliability was examined using the intraclass correlation coefficient (ICC_2,1), standard error of the measure (SEM), coefficient of variation (CoV), and minimal difference (MD) for each variable. There were no differences in CP, CHR, HR_avg, or TLim except P₄ T_Lim. The CP (ICC = 0.901, SEM = 11.7 watts, CoV = 6.13%, MD = 32.4 watts), CHR (ICC = 0.705, SEM 8.3 beats.min^-1, CoV = 5.13%, MD = 23.1 beats.min^-1), and P1-P4 HRavg (ICC = 0.757-0.935, SEM = 2.53-5.65 beats.min^-1, CoV = 1.59-3.56%, MD = 7.00-15.66 beats.min^-1) that demonstrated strong to moderate reliability, while P₁-P₄ TLim (ICC = 0.035-0.813, SEM = 0.32-1.75 min, CoV = 7.95-22.95%, MD = 0.90-4.85 beats.min^-1) demonstrated moderate to poor reliability. Fatigue thresholds such as CP and CHR may provide a more reliable and sensitive method of evaluating a change in exercise performance than a single performance measure.