Muñoz de la Cruz 2023 — Daily VBT load adjustment beats fixed loads on every outcome

Muñoz de la Cruz and colleagues took two groups of experienced sprinters through six weeks of identical resistance training, with one variable changed: how loads were prescribed each day. The control group used fixed loads (typical % 1RM prescription). The intervention group used VBT to adjust each day’s loads based on bar speed. Across every outcome measured — strength, jumps, sprint — the VBT-adjusted group came out ahead.

How to read this chart

Five outcome categories across the bottom: squat 1RM, countermovement jump, squat jump, 30 m sprint, and 30 m flying sprint. Teal bars are the fixed-load group, signal-lime bars are the VBT-adjusted group. Y-axis is percentage change in performance from baseline.

The biggest absolute gap is on squat weight (14.5 % vs 9.0 %) — VBT prescription gained ~60 % more strength than fixed loads. The 30 m sprint outcome is small but worth noticing: the fixed-load group went backwards (-0.5 %) while the adjusted group held even (+0.2 %). Sprinters can’t afford to lose top-end speed during a strength block; this chart says daily auto-regulation prevents that.

When to use this evidence

• Justifying VBT in sport-specific contexts. This study used experienced sprinters, not bodybuilders or recreational lifters. The transfer to field tests (sprint, jump) is what matters for athletic populations.
• Defending daily auto-regulation. Same exercises, same volume, same exercise order — only the day-by-day load adjustment differed. The chart isolates the auto-regulation effect.
• Programming during competition / in-season blocks. Daily readiness varies more in-season than off-season. VBT-adjusted prescription holds the relative load constant against that variability.

Why fixed loads under-perform

Fixed-load prescription assumes the athlete’s 1RM is stable across the week. It isn’t (see the daily 1RM fluctuation chart). On bad days, fixed loads land too heavy and fatigue compounds; on good days, they land too light and the stimulus is wasted. Across six weeks, those mis-prescriptions accumulate. VBT-adjusted prescription corrects for daily readiness in real time — every working set lands at the intended relative intensity regardless of how today’s nominal max would feel.

Pitfalls

• Population-specific. Experienced sprinters carry different recovery profiles, training history, and competing demands than recreational lifters or strength-sport athletes. The effect direction generalises; the magnitude likely shrinks in less-elite cohorts.
• Six-week intervention. Effect sizes this large in six weeks would partially regress over longer blocks as both groups approach physiological ceilings. The direction is robust; the size shrinks with longer studies.
• VBT requires hardware + skill. “Daily VBT-adjusted prescription” sounds clean in print but requires a measurement device, set-up time, and an athlete who knows their working velocities. Adoption cost matters; this chart shows the payoff once that cost is paid.

Where to go next

For the conceptual case underneath this finding, see the daily 1RM fluctuation chart — the day-to-day variation that fixed-load prescription can’t see. The companion comparison in trained males (not sport athletes) is the VBT vs %-based training chart (Vasiljevic 2024). For the practical “how to set up VBT-adjusted loads” guide, 1RM and VBT — a complete guide walks through the protocol.