The reliability of responses to repeated laboratory assessment: the evaluation of a preload-performance protocol in runners

A number of protocols associated with endurance performance have been presented in the literature where participants have had to endure a ‘preload’ phase (at a fixed relative intensity) followed by a ‘performance’ self paced phase. These protocols potentially could be used to assess athletic ability, to track changes in training status, and to assess the effect of ergogenic supplementation on performance. Identifying the reliability of this type of exercise protocol enables researchers to contextualise the responses observed with the random variation of measurement. Therefore the aim of this study was to assess the reliability of physiological responses prior to, during and post a preload endurance protocol, and assess the reliability of subsequent performance.

Twelve recreational endurance runners (8 Male, 4 Female, Age 40.2 ± 6.4 years, Height 1.73 ± 0.09m, Mass 71.0 ± 13.8kg) completed five visits to the laboratory. During the initial visit VO2max was assessed, the remaining four trials consisted of a 90 minute run at 65% VO2max (preload phase), which was then immediately followed by a 5 km time trial (performance phase) where participants could only view distance completed. Pre and post the preload phase, body mass (kg), haemoglobin (g.dL-1), haematocrit (%), core temperature (OC), urine specific gravity and blood lactate concentration (mMol.L-1) were recorded. At 30 minute intervals during the preload phase, running economy (kcal.km-1) estimated through indirect calorimetry, and blood lactate concentrations were assessed. Heart rate (beats.min-1) was measured throughout the preload phase at 5 s intervals. The reliability of all of these measures and time to complete the time trial phase of the protocol were then assessed.

The Coefficient of variation (CV) and 95% confidence limits were calculated across the four trials. The reliability coefficients of pre and post measures are shown in table 1. During trial measures for running economy, blood lactate concentration and heart rate derived CV’s of 2.67% (2.15-3.51%) and 25.08% (20.23-33.01) 2.69% (2.17-3.54) respectively. A CV of 4.28% (3.45-5.63%) was calculated for the time (s) to complete the 5km time trial.

Table 1. The coefficient of variation of measures pre and post the preload phase.
Parameter Pre trial Post trial
Nude Body Mass 0.69% (0.56-0.91%) 0.74% (0.60-0.97%)
Kitted Body Mass 0.57% (0.46-0.75%) 0.61% (0.49-0.80%)
Haemoglobin 5.19% (4.19-6.83%) 6.66% (5.37-8.77%)
Haematocrit 4.92% (3.97-6.48%) 3.67% (2.96-4.83%)
Core temperature 0.67% (0.54-0.88%) 0.80% (0.65-1.05%)
Urine Specific Gravity 0.30% (0.24-0.39%) 0.32% (0.26-0.42%)
Blood Lactate 19.45% (15.69-25.60) 33.73% (27.21-44.40)

Overall these data indicate the reliability of some key measurements used in the assessment of athletes in the laboratory. These data can be used to inform sample size estimations for future studies, and for the calculation of reference intervals for analysing and interpreting single case client data for scientific support.