(12) PREDICTION OF ONE REPETITION-MAXIMUM BASED ON THE LOAD-VELOCITY RELATIONSHIP: MULTIPOINT AND TWO-POINT APPROACHES

Since the load-velocity relationship displays strong linearity (R2 usually ≥ 0.9) in response to several multiarticular exercises, it has been argued that one-repetition maximum (1RM) can be predicted using this method. However, all past studies examining the predictive value of the load-velocity relationship in determining 1RM implemented its direct determination to enable testing movement velocity within a predetermined set of relative loads (e.g., 50, 60, 70, 80, 90% 1RM). Whether the two-point approach enables accurate predictions of 1RM without requiring its previous determination remains largely unknown. PURPOSE: To determine whether different approaches of establishing the load-velocity profile affect the accuracy of estimating 1RM.

Methods: We studied 26 young healthy male, physical education students, on no medications. All participants were well accustomed to resistance training, including the back-squat exercise. Predictions based on a novel two-point approach (no pre-determination of 1RM) were compared to those obtained with the conventional multipoint and two-point approach (with pre-determination of 1RM). After profiling the load-velocity relationship with each approach, 1RM was estimated relying on the general minimum-velocity threshold (MVT: 0.3 m.s-1). Analyses were conducted separately for the Smith-machine concentric back squat and free-weight eccentric-concentric back squat (n=13 Smith machine [23.3 ± 3.8 years]), n=13 free-weight [22.9 ± 3.2 years]). Differences in the load-velocity profiles obtained with each approach were assessed using slopes and y intercepts. The accuracy of 1RM prediction was determined by contrasting the actual with predicted 1RM and via Bland-Altman plots.

Results: Individual MVT did not differ from the general 0.3 m.s-1 value (0.27 ±  0.11 and 0.31 ± 0.08 m.s-1 , for Smith Machine and free-weight, respectively). The slopes (Smith Machine: -107 to -100.3; free-weight: -101.7 to -98.1 kg/ m.s-1 ) and y intercepts (Smith Machine: 133.3 to 137.4 kg; free-weight: 137.7 to 141.2 kg) were similar between approaches. For the Smith-machine, 1RM estimated with MVT did not differ from actual 1RM (103.5 ± 23.4 kg) with either approach (conventional multipoint: 103.2 ± 26.6 kg; conventional two-point: 103.4 ± 25.8 kg; novel two-point: 105.3 ± 24.7 kg; mean misestimate: -1.83-0.02 kg). However, the limits of agreement were high (~12 kg) and the absolute percent error was larger than zero with all approaches. Estimations of 1RM for the free-weight back squat were poor (conventional multipoint: 108.2 ± 11.1 kg; conventional two-point: 110.6 ± 11.9 kg; novel two-point: 110.7 ± 11.6 kg; mean overestimation of ~6-8 kg) and significantly different from actual 1RM (102.3 ± 10.5 kg; p< 0.05, except with multipoint).

Conclusions: For the Smith-machine concentric back squat, the combination of all profiling approaches with the use of a general MVT value enables accurate 1RM group estimations. For free-weight exercise, group estimations should be based on the multipoint approach. Yet, the wide limits of agreement preclude the use of these approaches for estimating 1RM accurately on an individual basis. PRACTICAL APPLICATION: Coaches and athletes can extract the load-velocity relationship without directly determining the 1RM. However, for accurate 1RM individual assessments, coaches and athletes should not rely on estimations based on the load-velocity relationship.

Acknowledgements: None