So What Happens?


As running speeds increase so do the activation of specific muscle groups causing different joint actions.  These increases are necessary for faster running speeds and knowing when and how these groups interact is important to help train speed.  What is especially important in regards to sprinting and acceleration, is the available time to produce force in most cases is less than .20-sec!  This means muscle contraction velocity, not necessarily maximal muscular force is key in faster running speeds. 

This isn't to say muscular force isn't important, but chasing peak muscular force, when an athlete cannot produce maximal muscular contractions in the necessary time frames is a circular endeavor. 

As an athlete increase his or her speed, muscles are shortened at increasingly higher velocities and have less and less time to generate the maximal forces.  What this means is that many factors, such as elastic response, pre-tensing, and joint stiffness are extremely important. 

With all that being said, specific musculature plays important roles during sprinting, whether it be concentrically, isometrically, or eccentrically in nature. 

Let's take a look at these muscle groups and the when, how, and what they do during the sprinting cycle.


Posterior Chain

The first hip extensor we'll look at are the glutes.  The glutes, specifically the glute max and glute medius, are maximized during ground contact to contribute to vertical support and stabilize the pelvis/hip to help prevent swinging, dropping, and over-rotation.

While the glute max does contribute and influence hip extension during ground preparation, it's major role is during ground contact to stabilize, resist deformation, and continue to transmit the energy built during ground prep.  In this position, the glutes are in a shortened position, and act in a very isometric manner.

It is apparent that at the start of the ground contact phase, at the point that the lead foot touches the ground, the hamstrings are functioning at relatively long muscle lengths. In contrast, at the same point in time, the gluteus maximus is functioning at a much shorter muscle length. Resistance training exercises often develop strength at specific joint angle ranges of motion depending upon their point of peak contraction. Therefore, these findings may be relevant for identifying the optimal resistance training exercises for training the hamstrings and gluteus maximus for optimal performance during sprint running. The hamstrings may benefit from being trained with exercises that involve a peak contraction at long muscle lengths, while the gluteus maximus may benefit from being trained with exercises that involve a peak contraction at short muscle lengths.

Ralph Mann, the famous sprint researcher, reported the best sprinters have the greatest hip extensor moments.   Bezodis et al. (2008) and Bezodis et al. (2009) both remarked upon the large hip extension moments that occurred during sprint running, providing strong support for their importance.

As the leg drives down towards the ground (what we call ground preparation), the hip extensors are the driver behind these forces and accelerating the leg, powerfully into the ground.

The next hip extensor we'll look at is the hamstring group.   The hamstrings are made-up of 3 muscles - bicep femoris, semitendinosus, and semimembranosus.  The group as a whole, is very active during the sprinting cycle and put under a ton of stress.

The hamstring group have the longest duration as they start activity at the beginning of ground preparation (at maximal hip flexion), and eccentrically contract - distally; while concentrically contract - locally, as they prepare for ground contact.   A recent review studied the mechanics of the hamstring during sprinting, here's what they found (6).

• The long head of the bicep femoris had the largest peak musculotendon strain (12.0% increase)
• The semitendinosus had the greatest musculotendon lengthening velocity.
• Semimembranosus produced the highest musculo-tendon force, absorbed and generated the most muscul-tendon power, and performed the largest amount of concentric and eccentric work.

As you can see, all the hamstring muscle undergo large changes in muscle length, but especially the bicep femoris with the greatest peak musculotendon strain which corresponds with the bicep femoris being the most injured hamstring muscle.   Overall, all the hamstrings are stretched to great degrees during ground preparation and at ground contact and the eccentric hamstring action during ground preparation is both reason for successful sprinting, but also increased risk of injury.

The hamstrings are the primary propulsive muscles during sprinting and as you can see above, they store elastic energy during the lengthening actions they go through which is then released at ground contact.

Unlike the glutes, hamstring force is lower during ground contact and higher during group prep.  This leads to a statement I use, and it leads to training methods for these muscles.

                                                                         "Glutes on the ground, hamstrings in the air"

The glutes work in a shorted position, isometrically at ground contact.  The hamstrings work eccentrically at the knee and concentrically at the hip, use a lot of stored elastic energy during ground preparation.  Studies have shown that mirroring your training to be specific to these actions of the hip extensors (eccentrically and elastically) to be successful in preventing and rehabbing from injury (9,10). 


Anterior Chain 

The anterior chain doesn't get as much love as the posterior chain, but they do play an important role during the sprinting cycle and are valuable in enhancing sprinting speed.

The first group we'll look at is the hip flexors, mainly the illiopsoas.  Two proposed ways increasing hip flexion strength increases sprinting speed is first it leads to a faster repositioning of the leg to get back to frontside mechanics. Second, the hip flexors are active during take-off and early flight to stop the leg from continuing to travel backwards and start the forward motion of the knee, this occurs in a stretched position and relies a lot on stored elastic energy.

Either way, hip flexion strength and cross sectional area has been positively correlated with faster sprinting speed (1,2,6,12)

Why are the hip flexors important?  Faster sprinters exhibit greater hip flexion and front side mechanics angle compared to slower sprinters (7).  At toe-off, the hip flexors are put under great stretch and the elastic components resist further hip extension and act like a rubber band to "snap" the hip back forward.

This means, the hip flexor complex needs to be trained at length and be able to utilize stored elastic energy to stop hip extension and "snap" the leg back to reach front-side mechanics. 

Another important aspect of the hip flexor group, is flexibility.  Riley et al. (2010) suggested that hip flexor mobility may play a role in the utilization of hip extension range of motion during running.  If contralateral hip flexor is adequate, proper and full hip extension can take place without running into restriction or co-contraction of the hip flexor group. 

The second part of the anterior chain is the quadrupeds group.  During the beginning of ground contact, the quadriceps eccentrically contract to stabilize the knee joint.  The primary role of the quadruped group is to provide high degrees of joint stiffness to support and absorb the vertical fall of the athlete.


Lower Leg

Ankle stiffness is key to transfer force produced up the chain into the ground and for muscles up the chain to work optimally.  For example, having instability in the ankle joint decreased the activity of the glute max by over 25% (3).  Instability goes in both directions - can't transfer force and leads to bigger engines not producing maximal force. 

We tell our athletes this analogy all the time.

                                      Having weak feet/lower leg is like having flat tires.  Even if you are driving a ferrari, 
                                                                             if you have flat tires the car won't go fast. 

It's the same thing with the feet/lower leg.  If they are weak, maximal force won't be transferred into the ground. 

The lower leg needs incredible amounts of isometric strength to resist the 4-6xBW forces being put onto them.  Longer duration, low-magnitude plyometrics are a great way to build lower log/foot strength, and as athletes progress high-magnitude plyometrics are great to simulate the GRF of sprinting.


Arms

Arms are an interesting topic in sprinting and do not play as big as a role as many state.  Let's be clear, the arms are neither the key to sprinting fast nor absolutely unnecessary to sprinting fast. They do play a role and assist in sprinting speed, specifically assist in horizontal propulsion during acceleration and vertical force during top-end sprinting, and they also help to counterbalance the rotary actions of the legs.  If one were not to use their arms, they wouldn't be able to control the rotation the leg put onto the trunk.  So, in a sense the arms help to maintain and streamline the efficiency of the sprinting cycle. 

There are a couple of misconceptions about the arms... THEY DO NOT LEAD THE LEGS and THEY DO NOT STAY LOCKED AT 90-DEGREES. 

We want to see the arms act in opposition of the legs while also matching timing and magnitude of the legs.  Finally, it is fully expected to see extension and flexion at the elbow joint during forward and backward swing, and these should also match each other (elbow flexion on forward swing should be matched by elbow extension on backward swing).


Practical Applications

Knowing what and when things happen during the sprint cycle means a lot in terms of dictating a training plan.  When we think of muscles, we think about strength, and when we think of strength, especially lower body - we think squat, deadlift, and maybe the Olympic lifts. 

While these things do inherently play a role, I highly doubt increasing squat or deadlift or Olympic lift strength will lead to greater horizontal or vertical forces during the sprinting cycle.  I think it would be very interesting to compare GRF during acceleration and top-end speed with strength in your typical lifts - squat, deadlift, Oly's.  I'm really skeptical that strength in these lifts relates to higher GRF's, vertical or horizontal, during acceleration and/or top-end speed. 

For higher level of mastery athletes, using these tools are limited at best and specific tools need to be used to enhance the qualities discussed in this article.  In fact, multiple research reviews have shown that traditional strength training is moderate at best for improving sprinting speed, and this relationship goes down as the level of the athlete increases (13,14).  And for those who think the almighty squat is the key to speed, know that wussy movements like the bulgarian split squat and unilateral jumps appear to more effective at enhancing speed (15,16,17).

Specificity is a must for high transfer to sprinting speed, especially for higher level athletes.  For example, the hamstrings are active during ground preparation, when the hip is flexed and the knee extends eccentrically.  This is in opposition of what many hamstring specific exercises or rehab program utilized.

Understand that strengthening the hamstrings are best trained at long lengths and eccentrically where the hip is kept in flexion.  Also, using SSC concepts on the hamstring prepares the body for specific transfer to performance (10,11).  Lastly, remember,

"Glutes on the ground, Hamstrings in the air"
​
Training the hamstrings in a unilateral, open chain manner is specific to the manner of execution an athlete needs.  Here are some ideas for training the posterior chain for greater transference to sprinting speed.

Here are some for the anterior chain

References:

1.  Deane, R. S., Chow, J. W., Tillman, M. D., & Fournier, K. A. (2005). Effects of hip flexor training on sprint, shuttle run, and vertical jump performance. The Journal of Strength & Conditioning Research, 19(3), 615-621.

2.  Dorn, T. W., Schache, A. G., & Pandy, M. G. (2012). Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance. The Journal of experimental biology, 215(11), 1944-1956.

3.  Webster, K. A., & Gribble, P. A. (2013). A comparison of electromyography of gluteus medius and maximus in subjects with and without chronic ankle instability during two functional exercises. Physical Therapy in Sport, 14(1), 17-22.

4. Bezodis, I. N., Kerwin, D. G., & Salo, A. I. (2008). Lower-limb mechanics during the support phase of maximum-velocity sprint running. Medicine and Science in Sports and Exercise, 40(4), 707.

5. Bezodis, I. N., Salo, A. I., & Kerwin, D. G. (2009). Athlete-specific analyses of leg joint kinetics during maximum velocity sprint running.

6. Schache, A. G., Dorn, T. W., Blanch, P. D., Brown, N. A., & Pandy, M. G. (2012). Mechanics of the human hamstring muscles during sprinting. Med Sci Sports Exerc, 44(4), 647-58.

7. Mann, R. (2011). The mechanics of sprinting and hurdling. CreateSpace.

8. Riley, P. O., Franz, J., Dicharry, J., & Kerrigan, D. C. (2010). Changes in hip joint muscle–tendon lengths with mode of locomotion. Gait & posture, 31(2), 279-283.

9. Brughelli, M., & Cronin, J. (2007). Altering the length-tension relationship with eccentric exercise. Sports Medicine, 37(9), 807-826.

10. Aquino, C. F., Fonseca, S. T., Gonçalves, G. G., Silva, P. L., Ocarino, J. M., & Mancini, M. C. (2010). Stretching versus strength training in lengthened position in subjects with tight hamstring muscles: a randomized controlled trial. Manual therapy, 15(1), 26-31.

11. Guex, K., & Millet, G. P. (2013). Conceptual framework for strengthening exercises to prevent hamstring strains. Sports Medicine, 43(12), 1207-1215.

12. Copaver, K., Hertogh, C., & Hue, O. (2012). The effects of psoas major and lumbar lordosis on hip flexion and sprint performance. Research quarterly for exercise and sport, 83(2), 160-167.

13. Rumpf, M. C., Lockie, R. G., Cronin, J. B., Jalilvand, F., & Street, D. (2015). The effect of different sprint training methods on sprint performance over various distances: a brief review. Journal of strength and conditioning research/National Strength & Conditioning Association.

14. Cronin, J., Ogden, T., Lawton, T., & Brughelli, M. (2007). Does Increasing Maximal Strength Improve Sprint Running Performance?. Strength & Conditioning Journal, 29(3), 86-95.

15. Speirs, D. E., Bennett, M., Finn, C. V., & Turner, A. P. (2015). Unilateral vs Bilateral Squat training for Strength, Sprints and Agility in Academy Rugby Players. Journal of strength and conditioning research/National Strength & Conditioning Association.

16. Holm, D. J., Stålbom, M., Keogh, J. W., & Cronin, J. (2008). Relationship between the kinetics and kinematics of a unilateral horizontal drop jump to sprint performance. The Journal of Strength & Conditioning Research, 22(5), 1589-1596.

17. McCurdy, K., Walker, J., Guerrero, M., & Kutz, M. (2010). The Relationship Between Unilateral And Bilateral Jump Kinematics And Sprint Performance.The Journal of Strength & Conditioning Research, 24, 1.