Profiling the Aerobic Window of Horses in Response to Training by Means of a Modified Lactate Minimum Speed Test: Flatten the Curve

There is a great need for objective external training load prescription and performance capacity evaluation in equestrian disciplines. Therefore, reliable standardised exercise tests (SETs) are needed. Classic SETs require maximum intensities with associated risks to deduce training loads from pre-described cut-off values. The lactate minimum speed (LMS) test could be a valuable alternative. Our aim was to compare new performance parameters of a modified LMS-test with those of an incremental SET, to assess the effect of training on LMS-test parameters and curve-shape, and to identify the optimal mathematical approach for LMS-curve parameters. Six untrained standardbred mares (3–4 years) performed a SET and LMS-test at the start and end of the 8-week harness training. The SET-protocol contains 5 increments (4 km/h; 3 min/step). The LMS-test started with a 3-min trot at 36–40 km/h [until blood lactate (BL) > 5 mmol/L] followed by 8 incremental steps (2 km/h; 3 min/step). The maximum lactate steady state estimation (MLSS) entailed >10 km run at the LMS and 110% LMS. The GPS, heartrate (Polar^®), and blood lactate (BL) were monitored and plotted. Curve-parameters (R core team, 3.6.0) were (SET) VLa₁._5/2/4 and (LMS-test) area under the curve (AUC_>/<LMS), LMS and Aerobic Window (AW) via angular vs. threshold method. Statistics for comparison: a paired t-test was applied, except for LMS: paired Wilcoxon test; (p < 0.05). The Pearson correlation (r > 0.80), Bland-Altman method, and ordinary least products (OLP) regression analyses were determined for test-correlation and concordance. Training induced a significant increase in VLa₁._5/2/4. The width of the AW increased significantly while the AUC_</>LMS and LMS decreased post-training (flattening U-curve). The LMS BL steady-state is reached earlier and maintained longer after training. BL_max was significantly lower for LMS vs. SET. The 40° angular method is the optimal approach. The correlation between LMS and V_MLSS was significantly better compared to the SET. The VLa₄ is unreliable for equine aerobic capacity assessment. The LMS-test allows more reliable individual performance capacity assessment at lower speed and BL compared to SETs. The LMS-test protocol can be further adapted, especially post-training; however, inducing modest hyperlactatemia prior to the incremental LMS-stages and omitting inclusion of a per-test recovery contributes to its robustness. This LMS-test is a promising tool for the development of tailored training programmes based on the AW, respecting animal welfare.

A modified D-max method to estimate heart rate at a ventilatory threshold during an incremental exercise test

The purpose of this study was to design a modified D-max method to determine heart rate at a ventilatory threshold (HRVT) and to investigate whether this method would be valid during incremental exercise tests. The HRVT was estimated from a new parameter defined as HR at the maximal difference point between linearly- and quadratically approximated HR trends (modified D-max method). HR and ventilatory gas data for 105 subjects (53 males and 52 females; 38.26 ± 12.06 years; 166.62 ± 8.21 cm; 65.31 ± 11.10 kg) were simultaneously collected during an incremental treadmill test to evaluate the validity of the modified D-max method. Reference HRVTs were manually identified from the ventilatory gas data by an experienced sports physiologist and compared with those estimated by the HR parameter. A strong positive correlation (r = 0.71, p <; 0.01) and a low HR difference of 9.94 ± 7.10 bpm between the reference and estimated HRVTs were obtained. The results indicate that the modified D-max method outperforms the conventional D-max method (r = 0.53, p <; 0.01), the three-piece linear regression lines method (r = 0.42, p <; 0.01), and the parallel straight line slope method (r = 0.57, p <; 0.01). Furthermore, the modified D-max method improves the predictive accuracy of HRVTs by combining its result with subject's age. The combined parameters have a strong positive correlation with the reference HRVTs (r = 0.74, p <; 0.01) and a lower HR difference of 9.40 ± 6.91 bpm. The results suggest that the modified D-max method is highly applicable to predicting HRVTs during incremental exercise tests and also improves HRVT detection accuracy by combining its result with the subject's age.