Does muscle make you slower?

Speed comes from force per kilogram

In 2000, Peter Weyand's group tested 33 runners at top speed on a treadmill fitted with a force plate. Their top speeds ranged from 6.2 to 11.1 m/s. The fastest runners pushed down on the ground with about 1.26 times more force relative to bodyweight than the slowest, while the time it took to swing the leg forward for the next step did not differ between them. Faster runners got faster by hitting the ground harder for their size.

Weyand measured force divided by bodyweight because every kilogram you add has to be supported and driven on each step. Added mass helps your speed only if it brings more than its share of extra force.

A 2005 follow-up by Weyand and Davis looked at the world's 45 fastest men and women at each standard track distance from 100m to 10,000m between 1990 and 2003. One relationship between body mass, height and the ground force each event demands fit all of them. Sprinters were the relatively heavy, muscular group and distance runners the light one, because sprint speeds require the biggest forces.

Do stronger athletes sprint faster?

On average, yes. In 17 international soccer players, half-squat strength correlated strongly with 0–30m sprint times and with jump height. In 34 well-trained youth players, absolute squat strength had the strongest link with 5m times (r = −0.60), and strength relative to bodyweight had the strongest link with 20m times (r = −0.67). In that group, relative strength counted for more over 20m than over 5m.

Training studies show the link runs in the useful direction. A meta-analysis of 15 studies and 510 subjects found that gains in back-squat strength went with faster sprinting, with a mean sprint improvement of 3.11%. In that analysis, the average load used (as a percentage of one-rep max) and the length of the program did not change how much sprint times improved. A broader review of strength research concluded that stronger athletes jump, sprint and change direction better.

How elite sprinters are built

Miller and colleagues scanned the legs of elite sprinters (about 10.10s 100m equivalent), sub-elite sprinters (about 10.80s) and untrained men with MRI. Total lower-body muscle climbed with ability:

Where the muscle sat mattered most. The elite group's hip extensors were 32% larger than the sub-elite group's, and still 15% larger per kilogram of bodyweight. Gluteus maximus volume alone explained 34–44% of the spread in sprint times. The plantarflexors (calf muscles) were no bigger in the elite group, and isometric strength tests did not separate the two sprint groups or relate to their times.

Both sprint groups were stronger than the untrained men, so strength mattered for getting to a sub-elite level. Among trained sprinters, though, a bigger isometric number on its own did not mark the faster runner, while bigger hip muscles did. That suggests a sprinter who already lifts well has more to gain from turning strength into ground force, through sprinting and jumping, than from chasing a bigger max.

Sprinters are also lean and fairly uniform in build. A study of 86 world-class sprinters found lower body mass index than the general population, less variation in body mass, and no single best height. Tall and short runners both reach the top, within a range that leaves out the extremes. For how those builds turn into speed, see how fast a human can run.

When extra mass slows you down

By the logic of Weyand's force data, any kilogram that does not raise the force you put into the ground is a kilogram you have to carry, so gaining weight without gaining force lowers your force per kilogram. The MRI data add that the muscle separating faster sprinters from slower ones sits in particular places, with the hip extensors and gluteus maximus at the top of the list, so overall size makes a poor training target.

Training order can slow you down too. Heavy lifting before sprinting means your fast reps happen on tired legs. The Sprint University program puts the sprinting first and the lifting after.

Lifting that transfers to speed

The program adds two or three lifts to the hard track days, after the sprinting. Over six weeks the main barbell lift follows a triphasic wave of slow eccentrics, then isometric holds, then explosive concentrics. Sets stay short (about two quality reps at roughly 82–85% of max) so every rep is fast, and max-velocity sprinting never shares a day with heavy squats or deadlifts. The speed training guide shows where those days sit in a week.

Jumps carry the force into fast, elastic contacts. Bounds, hurdle hops and depth jumps are in plyometrics for sprinters, and the full plan for sprinting, lifting and jumping together is in how to run faster.

Common mistakes

Training for size alone

Elite sprinters' extra muscle sat in specific hip muscles. Choose lifts that drive force into the ground and keep the reps fast.

Chasing a number on the scale

Speed depends on force relative to bodyweight. Weight gained without strength gained works against you.

Lifting before sprinting

Sprint first on fresh legs, then lift.

Never checking the transfer

Retest a sprint after each block. If your lifts rise and your times don't, change the plan.