REF-1162 · Varovic et al., 2025 · Applied Physiology, Nutrition, and Metabolism · Paper · PubMed

Can isometric holds replace full-range lifting for quad size?

In 23 trained lifters over 6 weeks, long-length isometric knee extension grew the front thigh about as much as full-range reps (difference -0.20 cm, uncertain).

B+moderate evidenceMeasured on trained athletes

Varovic, Zganjer, Wolf, Androulakis-Korakakis, Schoenfeld and Mikulic compared isometric knee extension held at long quadriceps length (ISOM) with full-range-of-motion isotonic knee extension (ISOT) in 23 resistance-trained men and women. Each person trained one leg each way, twice a week for six weeks.

Muscle thickness was measured by ultrasound at proximal, middle and distal sites of the front and side of the thigh. The between-condition estimate for summed anterior thigh thickness was -0.20 cm (95% high-density interval -0.54 to 0.16), with an 87% probability that the true difference favours ISOM and 75% of the posterior outside the region of practical equivalence.

The proximal anterior thigh showed the biggest lean toward ISOM (-0.11 cm, 95% HDI -0.24 to 0.02). The side of the thigh barely changed in either condition. The authors conclude the two methods produced similar quadriceps hypertrophy, with a possible proximal advantage for long-length holds that needs confirming.

Protocol

Participants: 23 healthy resistance-trained men and women (split, age and training history not in the abstract).
Design: within-subject; legs randomised to unilateral ISOM or ISOT knee extension; 2 sessions a week for 6 weeks.
Kind of isometric: knee extension held at long quadriceps length (deep knee flexion). Whether the hold was pushing (overcoming) or holding (yielding), its intensity, hold time, sets and how volume was matched are not given in the abstract.
Comparator: full-range isotonic (lifting and lowering) knee extension.
Outcome: muscle thickness at proximal, middle and distal anterior thigh and lateral thigh, before and after; Bayesian linear mixed-effects models with a region of practical equivalence (ROPE).

Key Results

Outcome (ISOT minus ISOM; negative favours ISOM)Estimate95% HDIBayesian summary
Summed anterior thigh thickness-0.20 cm-0.54 to 0.1687% probability of direction; 75% of posterior outside the ROPE
Proximal anterior thigh-0.11 cm-0.24 to 0.0282% of posterior outside the ROPE; largest shift toward ISOM
Lateral thigh (summed and regional)minimal to negligible change in both conditionsnot given
n = 23 participants (46 legs).

Mechanisms

Authors' interpretation: long-length isometric training can match the hypertrophic stimulus of full-range lifting, possibly with a regional (proximal) advantage.
Inference: the result is consistent with the idea that tension at long muscle length is a strong growth stimulus (REF-680); the abstract gives no mechanistic measure.
Inference: a summed difference of -0.20 cm with a 95% interval from -0.54 to +0.16 cm cannot exclude a modest advantage for either method.

Practical Application

Can isometric holds replace full-range lifting for quad size? In 23 trained lifters over 6 weeks, long-length isometric knee extension grew the front thigh about as much as full-range reps (difference -0.20 cm, uncertain).
The estimate leaned toward the isometric leg, most at the proximal thigh, but the interval included no difference. Muscle thickness only in the abstract; no strength results reported there.
Use it when full range hurts or is unavailable. A knee that tolerates a held deep angle but not loaded movement can still be grown with long-length holds; that application is the base's, not a tested rehabilitation outcome.
Do not read it as "isometrics are better for hypertrophy". The authors themselves say uncertainty precludes a definitive conclusion; the same group's 2025 meta-analysis of dynamic training found no meaningful long-length advantage (see Limitations).
For an endurance athlete the base's default stays dynamic heavy lifting ([SYNTH-43], [SYNTH-44]); isometric holds are a tool when movement is limited or fatigue must be kept low.

Limitations

From the abstract: hold intensity, duration, sets, volume matching, the isometric type, sex split, dropouts and the exact knee angle are not reported there.
Short (6 weeks, 12 sessions), one exercise, one muscle group; ultrasound thickness, not volume; the abstract reports no strength or performance outcomes.
Within-subject unilateral designs can be affected by cross-education between legs, which would shrink any true difference.
The same first and senior authors also published (June 2025, before this trial's PubMed record) a Bayesian meta-analysis of 12 trials, mostly dynamic (REF-1168), that found training at longer mean muscle lengths gave trivial regional-hypertrophy differences (SMD 0.05-0.09).
Funding: Europe PMC lists STRCNG Incorporated (trading as Jeff Nippard Fitness), a commercial fitness-content company, as funder. Conflicts (PubMed record): Schoenfeld previously served on the scientific advisory board of Tonal Corporation, a fitness-equipment maker; the other authors declare none.
How this entry was checked and changed
Why this level

within-subject design with n=23 (counts like a crossover with ≥15); short (12 sessions), one exercise, muscle thickness by ultrasound only; from the abstract