Dynamo Dresden ran 18 half-hour single-leg balance sessions with academy players. Forward-reach gap between legs: 9.2% to 4.1%. Landing gap between legs: not significantly changed. The test you pick decides the asymmetry you see.

Dynamo Dresden: focused beat mixed on the forward-reach gap

The Frontiers in Sports and Active Living trial at SG Dynamo Dresden was run inside a working academy, on academy-age players, during the competitive season — closer to a club coach’s working conditions than most asymmetry research, which has tended to use small samples, injured players, or older adults.

It also tested a question coaches argue about: is it better to drill the weak side with one focused method, or combine methods to cover more bases? Sixty-four male players from the U13, U15 and U17 squads were split three ways — single-leg balance training, balance plus jump training, or a stretching control. Sixty finished. Both training groups worked the non-kicking leg — the leg they stand on when they strike the ball — for nine weeks: twice a week, 30 minutes per session, on top of normal training and matches. Attendance was near-perfect across all three groups.

The balance-only group did four sets of 60–90 seconds on balance boards, spinning tops, BOSU balls and balance pads. Sessions got harder by lasting longer and by moving from solid ground to foam or wobbly surfaces.

The combined group split each session between two balance sets and single-leg jumps — squat jumps, countermovement jumps, broad jumps, drop jumps, box jumps and hurdle jumps. The control group stretched.

Three tests measured the result. The Y Balance Test has the player stand on one leg and reach as far as possible with the other in three directions: forward, back-and-in and back-and-out. For the single-leg drop-landing test, the player drops off a small box onto one leg and tries to stick the landing. The smaller EMG subgroup used skin sensors to read how hard a muscle was firing.

On the Y Balance forward reach, the balance-only group’s side-to-side gap dropped from 9.2% to 4.1% — a real, moderate-to-large improvement. The combined group barely shifted (5.3% to 5.1%). The control group barely shifted (6.0% to 5.7%).

The single-leg landing gap did not significantly change in any group. Calf-muscle activity differences between sides did get smaller in the 17-player sensor subgroup, but that change happened across all three groups, including the stretchers — so the balance work cannot take the credit.

Two things follow for a coach. First, on this one test — the forward reach — the focused group beat the mixed group, even though the mixed group was doing more types of work. Splitting the 30 minutes between balance and jumps watered down the balance dose enough that the forward-reach number did not move. That is one test, not a universal training rule, but it is a useful warning against assuming “more variety = more thorough.”

Second, the same nine-week block that improved the forward-reach gap did not significantly improve the landing gap. Same players, same training, same legs — different test, different answer. That is the case against running one screening test and calling it your asymmetry profile.

The trial does not show that this block lowers injury risk, or that it works the same way for senior players or female footballers.

“Asymmetry” is not one number

That second finding — same training, different test, different answer — is not a Dresden quirk. It is what the wider literature has been saying.

A 2026 Frontiers editorial on muscle asymmetry describes it as differences between sides in strength, power, muscle size or muscle activity — and then adds balance, flexibility, stiffness, range of motion and movement patterns on top.

The editorial also flags a problem with the tools. Two common ways of testing the muscle — one a strength machine, one a small electrical-pulse device — did not agree with each other. They are measuring different things, not the same thing through different windows.

For a club, the practical question is not “which is the bad leg?” It is which test exposes the gap, whether the same leg keeps showing up as the weaker one, and whether the training block actually targets the quality the test picked up.

Which leg is better can flip from test to test

Size of the gap is one thing. Which leg comes out on top is another, and it is the one most coaches skip.

A Journal of Human Kinetics study of 16 semiprofessional male players found no player kept the same “better leg” across every test. A player’s better side for ankle range could be the worse side in eccentric or iso-inertial strength work, and a different side again in a 180-degree turn. Which means a coach picking a side to load extra in the gym is picking one based on the test that happened to be run, not on a fixed property of the player.

How you do the math matters too. Bishop, Read, Lake, Chavda and Turner’s Strength & Conditioning Journal guide to calculating asymmetry walks through which formulas to use depending on whether the test uses both legs at once or one leg at a time. Switching formulas, changing which leg you use as the reference, or mixing the two can create movement on the spreadsheet that is not real change in the player.

The link to performance is real, but small

A 2023 PLOS ONE review pooled 11 studies and 283 adult athletes, all using single-leg jump tests to measure asymmetry.

Vertical jump performance had no meaningful link to asymmetry. Change-of-direction and sprint times had links that were statistically real but small. The authors rated the overall evidence as low to very low quality because the studies only watched what was already there — they can show a relationship, but they cannot prove that fixing asymmetry will improve sprinting or cutting. Injury risk would need separate prospective evidence.

That pattern fits football. Two-legged jumping lets the stronger leg cover for the weaker one. Sprinting and cutting do not — each leg has to handle force on its own at speed, so a gap is more likely to show up there. Even so, the link is weak, not automatic.

Use a battery, not a verdict

In the studies above, balance, single-leg strength, eccentric or iso-inertial strength work, landing, ankle range and change of direction each surfaced different information.

The tests you pick should follow the player — position, injury history, age and what you are currently training for — rather than a generic left-vs-right check.

The Dynamo Dresden trial gives one clean lesson: if the target is balance control in a forward reach for academy boys, focused single-leg balance work can move the number in-season without taking much time off the pitch. It also warns against assuming a mixed session beats a focused one — more variety can mean less of the dose the player actually needs.

For performance profiling, later assessments can add speed, eccentric braking work and direction changes, because those are closer to the moments when football makes one leg brake, push and reorient the body alone.

Before you load up a player’s weak side this week, check which test actually flagged it. If the gap only shows up once you average several tests together, the problem might be in the math — not the player.