Blood Flow Restriction Raised Muscle Activation at Lower Power in 40-Man Trial

Forty men rode the same incremental cycling test twice, once with cuffs squeezing their thighs and once without, while six leg muscles were recorded. Muscle activation ran higher with the cuffs on, and it did so while the riders were producing less power.

Muscle activation during cycling with restricted blood flow was measured phase by phase in a randomized crossover trial published in Scientific Reports on September 28, 2026, and the pattern it found complicates a common assumption about why the method works.

The study came from Shahram Abbasi and Mehdi Khaleghi Tazji of the Department of Biomechanics and Sports Injuries at Kharazmi University in Tehran, Iran, with Ali Abbasi of the Department of Sport Sciences at Shiraz University. Forty recreationally active men completed incremental cycling sessions under two conditions: with blood flow restriction and as a control.

Surface electromyography recorded six muscles: rectus femoris, vastus medialis, vastus lateralis, biceps femoris, medial gastrocnemius and tibialis anterior. Crucially, the researchers separated each pedal revolution into its power phase and its recovery phase rather than averaging across the whole stroke.

That separation is the point of the paper. Most cycling electromyography reports a single number per muscle per stage, which can hide whether a change belongs to the driving half of the stroke, the returning half, or both.

More Muscle Activation, Less Power

The core result is a mismatch. Normalized muscle activation was higher in every recorded muscle, in both halves of the pedal stroke, with the cuffs inflated. Yet the riders stopped at a lower workload: 208.7 watts with a standard deviation of 11.0, against 225.0 watts with a standard deviation of 12.3 in the control condition.

Put plainly, the legs were working harder electrically to produce less mechanical output. That is the signature of a muscle operating under an oxygen supply constraint rather than one that has been given some extra training stimulus for free.

Two other whole-cycle descriptors moved the same way. Median frequency fell, and the threshold-defined activation duration lengthened, meaning each muscle spent a greater share of every revolution above its activation threshold.

What Phase-Resolved Muscle Activation Adds

Splitting the pedal stroke matters because the two halves do different jobs. The power phase drives the crank down and forward. The recovery phase mostly repositions the leg and, in most riders, contributes little propulsion.

If restriction only raised muscle activation in the power phase, the simplest reading would be that the driving muscles were compensating for reduced oxygen delivery. Muscle activation rose in both phases instead, which suggests the effect was not confined to the propulsive work.

The longer activation duration points the same way. A muscle that stays above threshold for more of each revolution has less of the brief unloading window that normally lets blood move through it between contractions.

The Co-Contraction Result Was Small

One of the more interesting questions the study asked was whether restriction changes how opposing muscles work against each other. Whole-cycle co-contraction between rectus femoris and biceps femoris showed only a small condition effect, reported at p equal to 0.035 with a partial eta squared of 0.109.

That is a statistically detectable but modest change. It suggests the coordination pattern between the front and back of the thigh survived the intervention largely intact, even as the amplitude of muscle activation rose across the board.

The authors are careful here. They note their data do not identify independent changes in coordination or joint stabilization, only that a co-contraction index computed from surface signals shifted slightly.

How the Muscle Activation Numbers Were Scaled

The amplitude figures in this trial are session-peak-normalized root mean square values. Each muscle signal is expressed as a share of the highest value that same muscle produced during that same session, rather than against a maximal voluntary contraction measured separately.

That choice carries a trade-off. It keeps the comparison internally consistent when electrode placement and skin conditions vary between visits, which suits a crossover design well. It also means the muscle activation figures describe relative behavior within a single ride, not an absolute share of what each muscle could produce at maximum.

Readers comparing these results against other restriction studies should check which scaling method was used. A muscle activation value reported against a maximal voluntary contraction and one reported against a session peak are not interchangeable, and quietly mixing the two is a common source of inflated claims.

Why the Amplitude Reading Is Easy to Overstate

Surface electromyography is often described in gym coverage as a measure of how much a muscle is being recruited. It is not. It records the summed electrical activity reaching the skin above a muscle, which is shaped by recruitment, by firing rate, by tissue between the electrode and the fiber, and by local blood flow itself.

Restricting blood flow changes several of those inputs at once. A higher muscle activation signal under a cuff therefore cannot be read as a clean count of extra motor units doing extra work, which is precisely why the authors framed their outcomes as functional myoelectric descriptors rather than neural ones.

This distinction has practical weight. Marketing around restriction training often leans on electromyography amplitude as evidence of superior muscle activation, and this trial shows the amplitude rising in a condition where measured performance fell.

How It Fits With Other Restriction Research

The training literature is more mixed than the mechanism stories suggest. A trial covered here on blood flow restriction added to remote bodyweight training found no extra benefit over the same program without cuffs, despite the mechanistic case for one.

Similar gaps appear elsewhere in performance testing. Work on lactate accumulation rate in cyclists and triathletes has shown how a physiological marker can track a performance variable closely without being the thing coaches should train directly.

The same caution applies in the weight room. Research on partial range of motion lifting and on cluster set structures in combat sport athletes both found acute physiological differences that did not translate into clearly superior outcomes over a full training block.

What Riders and Coaches Can Take From This

This was an acute study. It measured what happened during two sessions, not what happens after weeks of training, and it reported no strength, power or endurance outcomes at all. Acute changes in muscle activation are a starting point for a hypothesis, not a result a training plan can be built on.

With that framing, a few general points follow, none of them individualized advice:

• Higher muscle activation readings during a restricted session are not evidence that the session produced more adaptation.
• Expect lower peak power output when cuffs are applied, and plan session targets around that rather than against unrestricted numbers.
• Restriction work is usually prescribed at low loads or low intensities for a reason, and this trial reinforces that a ramp to exhaustion under a cuff is a different task from a ramp without one.
• Anyone with cardiovascular, clotting or circulatory conditions should treat cuff-based methods as a clinical question, not a training preference.

For most recreational riders, the practical reading is narrow. The cuffs change what the legs do during the ride. Whether that change is worth building a training block around is a separate question this study did not attempt to answer.

What the Next Study Needs to Show

The useful follow-up is a training trial, not another acute one. It would apply the same restriction protocol across several weeks, measure muscle activation alongside actual performance, and report whether the electrical changes seen here precede any measurable gain.

It would also help to test women and trained cyclists. A 40-man recreationally active sample answers a narrow question, and the phase-resolved method the authors introduced is worth applying to riders whose pedaling technique is already well established.