Strength
Narrative Review
2017
The Validity of Using Velocity to Estimate Intensity in Three Back-Squat Training Protocols
By Harry G. Banyard, Ken Nosaka, Kimitake Sato and G. Gregory Haff
International Journal of Sports Physiology and Performance, 12(9), pp. 1190-1197
<h2>Abstract</h2>
<p>This investigation evaluated the validity of using mean concentric velocity to estimate relative training intensity (as a percentage of <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="one-<a href="/terms/repetition-maximum/" class="term-link" data-slug="repetition-maximum" title="repetition maximum">repetition maximum</a>">one-repetition maximum</a>, %1RM) across three distinct back-squat training protocols. Trained male athletes completed maximal effort repetitions at loads ranging from 40% to 100% of 1RM under three conditions: a standard incremental loading protocol, a fatigue protocol, and a randomized loading protocol. Mean concentric velocity was measured using a linear position transducer at each load. Results demonstrated strong inverse relationships between <a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="relative load">relative load</a> and mean concentric velocity across all protocols, supporting the use of velocity as a proxy for training intensity. Individual load-velocity profiles were highly reproducible, though notable inter-individual variability was observed, underscoring the importance of individualized profiling rather than reliance on generic velocity-intensity tables. These findings validate velocity-based training (VBT) as a practical and objective method for prescribing and monitoring resistance training intensity, with particular utility in accommodating day-to-day fluctuations in neuromuscular readiness that render fixed percentage-based programming suboptimal [1].</p>
<h2>Introduction</h2>
<p>Accurate prescription of training intensity is fundamental to the optimization of resistance training adaptations. The dominant paradigm in contemporary strength and conditioning practice frames intensity relative to the athlete's <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="one-<a href="/terms/repetition-maximum/" class="term-link" data-slug="repetition-maximum" title="repetition maximum">repetition maximum</a>">one-repetition maximum</a> (1RM) — the maximal load that can be lifted through the full <a href="/terms/range-of-motion/" class="term-link" data-slug="range-of-motion" title="range of motion">range of motion</a> for a single repetition with proper technique. Prescriptions such as "80% of 1RM for 4 sets of 3 repetitions" are ubiquitous in the scientific and practitioner literature. However, percentage-based programming suffers from a critical limitation: the 1RM is not a fixed, static value. It fluctuates substantially from session to session as a function of fatigue state, <a href="/terms/sleep-hygiene/" class="term-link" data-slug="sleep-hygiene" title="sleep quality">sleep quality</a>, nutritional status, and psychological arousal — factors that are difficult to control and often poorly captured by a single periodic 1RM assessment [1].</p>
<p>A fundamentally different approach to intensity prescription has gained considerable traction: velocity-based training (VBT). The underlying principle exploits the well-established inverse relationship between <a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="relative load">relative load</a> (expressed as %1RM) and the maximal velocity at which that load can be lifted — the load-velocity relationship. As relative load increases, concentric velocity decreases in a predictable, near-linear fashion. At 1RM, by definition, velocity approaches a minimum value often termed the "minimum velocity threshold" (MVT), typically observed around 0.15-0.30 m/s in the back squat depending on individual characteristics [2].</p>
<p><a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="If">If</a> a sufficiently stable relationship between load and velocity can be established for an individual athlete, velocity measurement during a warm-up set can theoretically be used to estimate the current 1RM on any given training day, enabling real-time adjustment of training loads to reflect actual neuromuscular readiness. This approach holds the potential to make load prescription more responsive, precise, and individualized than traditional percentage-based methods [3].</p>
<p>The current investigation examined whether this load-velocity relationship remains valid and consistent across different testing conditions, including fatigue states, providing a direct empirical test of the practical validity of VBT intensity prescription.</p>
<h2>The Load-Velocity Relationship</h2>
<h3>Foundational Principles</h3>
<p>The load-velocity relationship in resistance exercise is grounded in the force-velocity relationship first described by A.V. Hill for isolated muscle preparations: as the force (load) imposed on a contracting muscle increases, the velocity of shortening decreases [1]. When this principle is applied to complex multi-joint exercises such as the back squat, the relationship between external load and mean concentric velocity remains robustly inverse, albeit influenced by additional factors including muscle architecture, limb mechanics, and the skill level of the athlete.</p>
<p>Empirical investigations have consistently demonstrated that the load-velocity relationship in the squat can be adequately described by a linear or slightly curvilinear model across the intensity range typically used in training (40-100% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>). Mean concentric velocity at 40% 1RM in trained athletes typically falls in the range of approximately 0.80-1.00 m/s, declining progressively to approximately 0.15-0.30 m/s at 1RM [2].</p>
<h3>Individual Load-Velocity Profiles</h3>
<p>A critical finding from the current and related investigations is the existence of substantial inter-individual variability in load-velocity relationships. While the direction of the relationship (higher loads = lower velocities) is universal, the specific velocity associated with a given %1RM differs meaningfully between individuals. This variability is attributable to differences in body proportions, fiber type composition, training history, and technical proficiency. Consequently, population-average velocity-intensity tables — where, for example, a velocity of 0.50 m/s is assumed to correspond to 75%1RM for all athletes — may introduce unacceptable errors in load prescription for specific individuals [1].</p>
<p>This finding strongly argues for the construction of individualized load-velocity profiles for each athlete. By measuring velocity across three to five submaximal loads during a familiarization or assessment session, a regression equation unique to that individual can be derived, enabling more accurate velocity-to-load conversion during subsequent training sessions.</p>
<h3>Protocol Sensitivity</h3>
<p>Across the three protocols evaluated in this investigation (incremental, fatigued, and randomized loading), the load-velocity relationship demonstrated reasonable stability, though fatigue conditions modestly attenuated velocity at any given absolute load — an expected consequence of reduced <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment capacity. This finding has practical relevance: <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> an athlete exhibits systematically lower velocities than their established profile would predict, this may signal inadequate recovery and warrant load reduction [3].</p>
<h2>Practical Applications of VBT</h2>
<h3>Daily <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> Estimation</h3>
<p>The most straightforward practical application of VBT is the estimation of an athlete's current 1RM on each training day without performing an exhaustive maximal effort test. By measuring mean concentric velocity during a standardized warm-up set at a known submaximal load and consulting the athlete's individual load-velocity profile, coaches can project the day's 1RM and set training loads accordingly. This is particularly valuable during competition preparation phases, heavy training blocks, or periods of planned high-volume loading when actual 1RM assessment is contraindicated due to fatigue [1].</p>
<h3>Velocity Loss as a Fatigue Indicator</h3>
<p>A secondary application involves monitoring intra-set velocity loss as an objective indicator of accumulated neuromuscular fatigue. As repetitions accumulate within a set, mean concentric velocity declines progressively. The magnitude of this velocity loss correlates with the degree of neuromuscular fatigue and metabolic disruption incurred during that set. Research suggests that velocity loss thresholds of approximately 20-25% for strength-focused training and 30-40% for <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>-focused training represent appropriate endpoints at which a set should be terminated [2].</p>
<p>This approach — termed "velocity-based set termination" — offers a mechanistic alternative to prescribing a fixed number of repetitions. Rather than performing a predetermined 3 repetitions regardless of effort level, the athlete performs repetitions until velocity drops by a specified percentage, automatically adjusting volume based on their neuromuscular state on that day. Athletes who begin a set in a fatigued state will accumulate the prescribed velocity loss more rapidly, naturally reducing repetition count and total volume — a built-in regulatory mechanism absent from traditional percentage-based programming.</p>
<h3>Technology Requirements</h3>
<p>Practical implementation of VBT requires a device capable of measuring barbell velocity in real time. Linear position transducers (LPTs), which attach to the barbell via a cable, provide highly accurate velocity measurements and are considered the research gold standard [3]. More recently, inertial measurement units (IMUs) and smartphone-based applications using accelerometer data have emerged as lower-cost alternatives, though their accuracy relative to LPTs requires case-by-case evaluation. The increased accessibility of these tools has made VBT feasible for a growing range of training environments beyond elite sport settings.</p>
<h2>Conclusions</h2>
<p>The present investigation supports the validity of using mean concentric velocity to estimate relative training intensity in the back squat across multiple testing protocols. The load-velocity relationship demonstrated sufficient stability and consistency to serve as a practical intensity prescription tool, particularly when individualized load-velocity profiles are employed rather than population-averaged reference values.</p>
<p>The data confirm that VBT offers a meaningful advantage over traditional percentage-of-<a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> programming by capturing day-to-day variability in neuromuscular readiness that fixed percentages cannot accommodate. Athletes whose actual 1RM is suppressed by fatigue or suboptimal recovery will naturally train at appropriately reduced absolute loads when velocity targets are used, preventing the accumulation of excessive fatigue that can result from rigidly adherent percentage-based programming [1].</p>
<h3>Limitations</h3>
<p>This study was limited to the back squat movement, and caution is warranted in generalizing these load-velocity relationships to other exercises. Upper-body movements such as the bench press and overhead press exhibit distinct velocity profiles and minimum velocity thresholds [2]. The athlete sample was also drawn from a trained population, and the applicability of these findings to novice or elderly populations requires separate investigation.</p>
<h3>Future Directions</h3>
<p>Future research should examine the long-term training outcomes of VBT-based programs compared to traditional percentage-based approaches, particularly with respect to strength development, <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>, and training readiness metrics. The development and validation of lower-cost measurement solutions will be essential for broadening the accessibility of VBT methodologies across a wider range of training contexts and resource environments [3].</p>
<p>In summary, velocity-based training represents a scientifically supported, practically implementable framework for intensity regulation in resistance training, offering practitioners a dynamic and responsive alternative to static percentage-based prescriptions.</p>