Reproducibility of Blood Lactate Concentration Rate under Isokinetic Force Loads.

(1) Background: Maximum isokinetic force loads show strongly increased post-load lactate concentrations and an increase in the maximum blood lactate concentration rate ( V ˙ La), depending on load duration. The reproducibility of V ˙ La must be known to be able to better assess training-related adjustments of anaerobic performance using isokinetic force tests. (2) Methods: 32 subjects were assigned to two groups and completed two unilateral isokinetic force tests (210° s, Range of Motion 90°) within seven days. Group 1 (n = 16; age 24.0 ± 2.8 years, BMI 23.5 ± 2.6 kg m, training duration: 4.5 ± 2.4 h week) completed eight repetitions and group 2 (n = 16; age 23.7 ± 1.9 years, BMI 24.6 ± 2.4 kg m, training duration: 5.5 ± 2.1 h week) completed 16 repetitions. To determine V ˙ La, capillary blood (20 µL) was taken before and immediately after loading, and up to the 9th minute post-load. Reproducibility and variability was determined using Pearson and Spearman correlation analyses, and variability were determined using within-subject standard deviation (S) and Limits of Agreement (LoA) using Bland Altman plots. (3) Results: The correlation of V ˙ La in group 1 was r = 0.721, and in group 2 r = 0.677. The S of V ˙ La was 0.04 mmol L s in both groups. In group 1, V ˙ La showed a systematic bias due to measurement repetition of 0.02 mmol L s in an interval (LoA) of ±0.11 mmol L s. In group 2, a systematic bias of -0.008 mmol L s at an interval (LoA) of ±0.11 mmol L s was observed for repeated measurements of V ˙ La. (4) Conclusions: Based on the existing variability, a reliable calculation of V ˙ La seems to be possible with both short and longer isokinetic force loads. Changes in V ˙ La above 0.11 mmol L s due to training can be described as a non-random increase or decrease in V ˙ La.