Identifying which strength training exercises are best for improving sprinting performance by asking experts is a very challenging task, as many of them disagree quite substantially with one another.
Fortunately, by looking at the factors that determine sprinting performance, we can identify the muscles that are used, and the types of strength that they need to display. Then we can work backwards from there to identify the best exercises.
What factors determine sprinting performance?
Comparing sprinters with non-sprinters, and higher-level sprinters with lower-level sprinters, reveals that athletes who can sprint faster have larger hamstrings, gluteus maximus, and hip flexor (psoas major and rectus femoris) muscles, while also displaying proportionally smaller quadriceps.
Studies using a range of other research methods have similarly shown that sprinting performance is determined primarily by the hip extensor muscles (hamstrings, adductor magnus, and gluteus maximus), hip flexor (psoas major and rectus femoris) muscles, and knee flexor muscles (hamstrings).
Let’s look at these muscles in groups, starting with the hip extensors.
#1. Hip extensors
During sprinting, the hip extensor muscles (hamstrings, adductor magnus, and gluteus maximus) produce the majority of their force while the foot is in contact with the ground.
The length of this period of ground contact time is extremely short (less than 150ms), and is much less than the time required for them to develop peak force. Additionally, this force is exerted while the leg is nearly straight, and the hip is extended, which means that the muscles need to produce force at joint angles corresponding to short fiber lengths.
Strength gains after training are very specific to both (1) the velocity, and (2) the joint angle used in training.
When we train using high-velocity exercises, like jump squats, we improve the ability to produce force at high velocities to a much greater extent than against very heavy loads, which require low velocities. This happens for a variety of reasons, including a very large increase in the rate of motor unit firing in the first 50ms of a contraction, and an improvement in the contractile ability of the muscle fibers which allows them to shorten more quickly.
In contrast, using heavy loads to improve maximum strength does not transfer as well to high-velocity force production as you might hope. Even though it produces increases in neural drive, it does not increase the rate of motor unit firing in the first 50ms of a contraction, and it reduces the contractile ability of the muscle fibers, and stops them contracting as fast.
When we train using partial range of motion exercises (or exercises that load the muscle most forcefully in the contracted position), we usually improve the ability to produce force in that range of motion to a much greater extent than in a similar, full range of motion exercise. This happens because contracting muscles at short lengths tends to produce strength gains predominantly by increases in neural drive that only apply to the trained joint angle, and not to other joint angles.
In contrast, using full range of motion exercises to improve strength at joint angles that correspond to partial ranges of motion is not quite as effective as you might hope. In the case of multi-joint lower body exercises, this happens mainly because the leverage of each of the working muscles changes with joint angle. So some muscles are trained to a greater extent at some joint angles than at others.
Overall, this means that we should train hip extension for sprinting using high-velocity exercises that load the muscles at short muscle lengths (in the contracted position), like jump squats, hex bar jumps, and heavy kettlebell swings. In contrast, traditionally-popular exercises like heavy parallel back squats are unlikely to be as effective, as they primarily improve heavy load, low-velocity strength at long muscle lengths.
#2. Hip flexors
During sprinting, the hip flexor (psoas major and rectus femoris) muscles produce the majority of their force while the foot is in the air. In other words, they recover the leg after it has been used to exert force into the ground.
After exerting force into the ground, the hip is fully extended, and the degree of hip extension is actually greater in faster sprinters (and not smaller, as the proponents of “front-side mechanics” have proposed). After reaching full extension, the sprinter has to recover this leg as fast as possible to the point where the thigh is just 20 degrees from a horizontal line parallel with the ground.
Indeed, since the frequency of strides is a key factor determining sprinting performance, faster recovery of the leg is likely to help a sprinter run more quickly, and this likely explains why the hip flexors are so important for sprinting.
This means that the hip flexors need to move the hip a high velocities through a large range of motion, starting from a long muscle length, and working all the way through to a contracted position. Consequently, we should train hip flexion for sprinting using high-velocity exercises that load the muscles through a full range of motion.
During sprinting, the hamstrings play a dual role. As mentioned above, they contribute to hip extension in the ground contact phase. Yet, they also have a very important role when the leg is in the air.
As the hip flexors bring the thigh through to the point where it is swinging parallel to the ground, the hamstrings begin producing force to help decelerate it, by acting as a hip extensor. Additionally, since the lower leg is starting to swing forward rapidly at this point, the hamstrings begin producing force to help decelerate it, by acting as a knee flexor.
At this point, the thigh and the lower leg have a great deal of momentum. So even though the hamstrings can exert a high level of force, they are still lengthened substantially when they attempt to contract. This means that they undergo an “eccentric” contraction, in which forces can be far higher than can be achieved in any normal strength training exercise, regardless of the weight used or the velocity.
When we carry out normal strength training with free weights or machines, we lift and lower the same weight. Since the force we produce is equivalent to gravity plus inertia in the lifting (concentric) phase, and gravity less inertia in the lowering (eccentric) phase, we actually produce less force in the lowering phase than in the lifting phase. Also, since we are 25–30% stronger in the lowering phase than in the lifting phase, lifting a weight that is 85% of our one repetition-maximum (1RM) is only 65% of our eccentric 1RM, when we come to lower it.
This means that unless we overload the hamstrings and make them lower a weight that they cannot lift, we will never be able to train them sufficiently for sprinting. This is why flywheel leg curls, Nordic hamstring curls, and other similar exercises are *indispensable* for improving sprinting performance, even though some traditional coaches dislike the idea of using exercises that work the knee flexors directly, and which are not performed while standing upright.
What is the takeaway?
For improving sprinting ability, we want to program strength training exercises that work the hip extensors using high-velocity exercises that load the muscles at short muscle lengths (in the contracted position), like jump squats, hex bar jumps, and heavy kettlebell swings. Similarly, we need to train the hip flexors using high-velocity exercises that load the muscles through their full range of motion, such as with ankle weights or elastic resistance.
Additionally, we want to ensure that the hamstrings are exposed to lowering a weight that they cannot lift, such as by using flywheel leg curls or Nordic hamstring curls, as this is the only way to expose them to the supramaximal forces that are exerted while they are in the air, as they try to decelerate the forward motion of the thigh and the lower leg.