Author(s): YEH, K., CHENG, H., LIU, H., Institution: NATIONAL TAIWAN NORMAL UNIVERSITY, Country: TAIWAN, Abstract-ID: 221

INTRODUCTION:
The load–velocity profile (LVP) is widely used in velocity-based training (VBT) to prescribe load based on concentric velocity at different percentages of one-repetition maximum (1RM). However, concentric velocity is influenced by eccentric phase execution. Variations in eccentric velocity modify muscle mechanics, affecting stretch–shortening cycle (SSC) expression and neuromuscular responses, potentially altering the load–velocity relationship structure. The extent to which eccentric velocity systematic manipulation influences LVP characteristics remains unclear. This study examined how three eccentric tempo conditions (4-second [4s], voluntary [VOL], and explosive [EXP]) affect concentric velocity and power output in parallel squat.
METHODS:
Twelve resistance-trained males (age: 24.0 ± 1.9 years; height: 1.75 ± 0.05 m; body mass: 76.9 ± 10.0 kg; 1RM: 140.6 ± 12.3 kg) performed parallel back squats under three eccentric tempo conditions across loads ranging from 20, 40, 60, 65, 70, 75, 80, and 90%1RM. Mean velocity (MV), mean propulsive velocity (MPV), mean power (MP), and mean propulsive power (MPP) were recorded using a linear position transducer. Data were analyzed using linear mixed-effects models with random effects and heterogeneous variance structures.
RESULTS:
Significant eccentric tempo × load interactions were observed for MV and MPV (p < 0.001), with EXP and VOL showing steeper negative load–velocity slopes than 4s condition. Across 20–90%1RM, VOL and EXP produced higher MV and MPV than 4s, whereas EXP exceeded VOL only at ≤70%1RM, with differences diminishing at ≥75% 1RM. These patterns were reflected in higher estimated loads at 1.0 m/s, with MV-based V1 values of 36.4, 49.0, and 51.8% 1RM and MPV-based V1 values of 45.1, 56.5, and 58.8% 1RM for 4s, VOL, and EXP, respectively. MP and MPP exhibited significant linear and quadratic load effects and main effects of condition (p < 0.001), with faster eccentric execution shifted the power–load curves upward, increased curve convexity, and resulted in higher peak MP and MPP (4s < VOL < EXP) (MP: 716.7, 815.4, 860.7 W; MPP: 761.9, 888.7, 942.8 W).
CONCLUSION:
Eccentric tempo significantly modified the LVP by altering both velocity magnitude and load–velocity structure. 4s condition resulted in flatter load–velocity slopes and reduced estimated loads at 1.0 m/s, indicating constrained velocity expression in the low-load region. In contrast, VOL and EXP produced steeper negative slopes and higher velocities at lighter loads, with differences diminishing as load increased. Eccentric tempo also influenced the power–load relationship, as faster conditions yielded higher and more convex curves with elevated peak power, whereas the 4s condition consistently showed lower MP and MPP. These findings demonstrate that eccentric execution systematically alters velocity–load and power–load characteristics, particularly at lighter loads, highlighting the need to standardize eccentric tempo when applying LVP for load prescription in VBT.