When it comes to sprinting, everyone loves to focus on stride frequency, ground contact time, arm swing and all the technical components that speed coaches love to throw around. But what people often forget is that sprinting performance, especially during the maximal velocity phase, is about how much force you can generate and a big part of that equation comes down to muscle size and specific muscle recruitment.

A research study done 2021 put a spotlight on the impact of individual hip extensor muscle size, particularly the semitendinosus (ST), and how it relates to sprint performance. I want to deep dive into how this plays into real-world training and why it’s crucial to target these specific muscles if your training goal is speed.

Muscle size of individual hip extensors in sprint runners: Its relation to spatiotemporal variables and sprint velocity during maximal velocity sprinting

Let’s start with the basics. The hip extensors are a group of muscles including the gluteus maximus and the hamstrings. When you sprint, these muscles play a role in generating horizontal force, driving your leg backward, and propelling your body forward. Sprinting isn’t just about how fast your legs can move through the air, it’s about how forcefully you can push into the ground, which directly impacts how fast you move forward. That backward push, known as hip extension, is powered by the glutes and hamstrings, specifically the semitendinosus.

This study showed that among the hip extensors, the “semitendinosus” was the standout muscle. Its volume (relative to body mass) had a clear relationship with sprinting speed, especially during the maximal velocity phase (50-60 meters into a sprint). The larger your ST muscle, the more ground you can cover with each stride, improving your overall sprint performance.

Here’s the interesting part, while increasing muscle size can generally help generate more force, not every muscle in the hip extensor group is equally important. The study found that other muscles like the gluteus maximus and other hamstring muscles, such as the biceps femoris, didn’t show the same relationship with sprint speed as the semitendinosus.

A targeted approach must be taken. Adding muscle mass could be detrimental, as increased body mass without the corresponding force/power could lead to slower sprint times. The takeaway from this research is that targeting specific muscles like the semitendinosus can lead to better sprint times without the addition of overall bulk.

The semitendinosus has longer muscle fibers compared to other hamstring muscles, which means it’s better suited for producing force at the high speeds during sprinting. It’s highly active during both phases of the sprint, particularly when you’re in the stance phase driving off the ground.

The goal when sprinting is to reduce ground contact time while maximizing the horizontal force you generate. The semitendinosus helps you achieve this by allowing for a long stance distance without wasting time on the ground.

The research supports this. The semitendinosus size was strongly correlated with both sprint speed and stance distance, meaning that the bigger and stronger your semitendinosus, the longer your stance phase can be – increased force production and improved efficiency in ground contact.

If your goal is to sprint faster, you need to focus on hypertrophying – we know this. General strength work  (GPP) will give you a base, but if you’re outcome requires speed, you need to be targeting movements that emphasize the hamstrings and more specifically the semitendinosus.

Movements like Nordic hamstring curls, Romanian deadlifts, and Bulgarian split squats target hip extension and knee flexion.  These exercises help build the semitendinosus and hamstring muscles in a way that directly translates to sprinting mechanics.

And while hypertrophy is always part of the picture, in Power Athlete and Johnnie Land, we never forget about neuromuscular training. The semitendinosus has to fire explosively during high velocity sprints, which means leaning heavy on plyometrics and speed drills that demand forceful hip extension.

Sprinting is about being strong in the right places. This study shows how important it is to focus on the semitendinosus for improving sprint performance. Not all muscles are created equal when it comes to speed so you need a plan.

Train smart by targeting the semitendinosus, and speed with better efficiency for longer distances at max velocity will be the outcome.