One Big Session or Three Smaller Ones? New Research Tests How You Should Split Your Weekly Sets

If you coach clients on a two- or three-day-a-week split, you've made this call without much hard data behind it: is it better to hammer a muscle group with all its sets in one session, or spread the same total volume across the week? A study published this month in the Journal of Strength and Conditioning Research put that exact question to the test in trained lifters, and the answer is more interesting than "more frequency wins."

What the study found

Researchers from the State University of Campinas (UNICAMP) in Brazil recruited 18 resistance-trained men and split them into two groups for a six-week lower-body program built around the back squat, leg press, and leg extension. Both groups performed the same prescription on paper: three sets per exercise per week, at 80% of their one-rep max, taken to concentric failure. The only variable that changed was how those three sets were distributed:

• RT1 did all three weekly sets for each exercise in a single session.
• RT3 spread the same three weekly sets across three separate sessions (one set per session).

Everything else, load, proximity to failure, exercises, and weekly set count, was held constant. This is what researchers call an "equal-volume, different-distribution" design, and it's exactly the kind of comparison that cuts through noisy real-world programming where frequency, volume, and intensity often change all at once.

The data, explained in plain English

Three things were tracked over the six weeks: volume load (total weight lifted, sets × reps × load), maximal strength (1RM on each lift), and quadriceps muscle thickness (measured at the vastus lateralis and mid-thigh, a proxy for hypertrophy).

Volume load diverged sharply. The group training three times a week racked up substantially more total tonnage than the once-a-week group, 58% more on the back squat (p = 0.010) and 76% more on the leg press (p = 0.013), with a similar trend on leg extension that just missed statistical significance (p = 0.057). The mechanism here is straightforward: when you're fresh for each set instead of grinding out set two and three while already fatigued from set one, you simply move more weight for the same number of reps at the same relative intensity.

Strength went up in both groups, with a hint that more frequency helped more. Everyone got stronger across the six weeks (p < 0.001 for the effect of time on all three lifts), which isn't surprising given both groups trained hard and progressed. But the between-group comparison, did RT3's extra volume load translate into extra strength, only approached significance on the back squat (p = 0.074) and leg press (p = 0.071), with the numbers trending in RT3's favor. The leg extension showed no such pattern (p = 0.535). In plain terms: there's a suggestive signal that distributing volume across more sessions gave a strength edge, but it wasn't statistically decisive in six weeks with 18 people.

Muscle thickness didn't care how the sets were split. Both groups gained muscle thickness over time (p < 0.001 and p = 0.001 at the two measurement sites), but there was no meaningful difference between groups (p = 0.215 and p = 0.987). Despite RT3 lifting substantially more total weight, it didn't grow more muscle than RT1 in this window.

Why it matters for training and coaching

This study lands right in the middle of an ongoing debate in strength and conditioning about how much "frequency" actually matters once weekly volume (sets) is matched. The headline takeaway isn't "train each muscle three times a week instead of once," it's more nuanced, and more useful, than that:

1. Session distribution is a lever for volume load capacity, not automatically for muscle growth. If a client can only fit in one heavy leg day a week, don't assume they're leaving hypertrophy on the table just because of the schedule, at least not over a 6-week block. The muscle thickness data here says the stimulus was similar either way when weekly sets were matched.
2. But there's a real strength-training argument for more frequent, lower-per-session volume. Being fresher for every set at 80% 1RM let the three-times-a-week group move meaningfully more weight. Even though it didn't reach statistical significance for strength gains in this short study, the directional trend, plus the well-established relationship between volume load and long-term strength adaptation, is a reasonable argument for spreading heavy work across more sessions when a client's schedule allows it, particularly for clients chasing 1RM performance rather than pure aesthetics.
3. Six weeks is short. The authors are clear this was a short intervention. Hypertrophy differences from a volume-load gap of 50-75% might simply need longer than six weeks to show up in muscle thickness measurements, or the extra tonnage in RT3 might not represent additional effective stimulus once each set is already taken to failure. Either explanation is plausible, and it's a reason to treat this as one data point, not gospel, the sample size (n=18) and short duration mean it should inform your programming logic rather than dictate it outright.
4. "Failure" sets may cap the stimulus regardless of load. Because every set in both arms was taken to concentric failure, the fatigue and mechanical tension per set were arguably already maximal, which may be exactly why more total weight didn't produce more muscle. This lines up with existing hypertrophy literature suggesting that once you're training close to failure, additional volume load yields diminishing hypertrophic returns, even as it can still support strength and work capacity.

Actionable advice for coaches and lifters

• For hypertrophy-focused clients with limited time: don't feel obligated to chase higher frequency splits if a single well-executed session per muscle group per week is all that fits. Prioritize hitting the target weekly sets close to failure over how those sets are distributed.
• For strength- or performance-focused clients: if schedule allows, consider spreading heavy compound work (squats, presses, pulls) across more sessions per week at the same weekly set count. You may unlock more total volume load, a variable more consistently tied to long-term strength progression, without adding net weekly sets.
• Match distribution to the goal, not habit. Powerlifting- or performance-oriented blocks: lean toward more frequent, lower-per-session volume. Physique/hypertrophy blocks on a tight schedule: don't stress about consolidating volume into fewer sessions.
• Re-evaluate over longer blocks. Because this trial ran six weeks, treat any strength-side advantage for higher frequency as provisional. Track it in your own client data over 8-12+ week blocks before treating it as settled programming doctrine.
• Watch volume load, not just set count, as a training variable. This study is a good reminder that "three sets" isn't a fixed stimulus, how fresh a client is for each of those sets meaningfully changes how much weight they can actually lift, which matters for progressive overload tracking.

Sources and references

• Calzavara, J. & Barroso, R. (2026). "Effects of Weekly Set Distribution on Volume Load, Lower-Body Strength, and Quadriceps Muscle Thickness in Trained Men." Journal of Strength and Conditioning Research (published ahead of print, Sept 8, 2026). PubMed PMID: 42709978 · DOI: 10.1519/JSC.0000000000005665

Study design note: single-site trial, n = 18 trained men, 6-week duration, a small, short-term sample; treat strength-side trends (p = 0.07-0.08) as suggestive, not conclusive.