October 31, 2014

RESEARCH: Enhancing Max Velocity Sprints with Weight Vests and Sled Pulls

A recent study on 20 college varsity lacrosse players from the Haverford College’s Athletic Department was performed by the University of Pennsylvania’s Human Performance Laboratory (Authors Clark, K., Stearne, D., Walts, C., and Miller, A. – Published in the December 2010 – Vol. 24 No. 12 Issue of the Journal of Strength and Conditioning Research) looking at the longitudinal effects of resisted sprint training using weighted sleds, weighted vests and non-resisted sprinting. In this post we will be giving our opinion on the training study and give some of our own experiences with this training modality.

The design of the study was built around the presupposition that, “Because of the acute increase in muscular force output required to overcome the drag of a weighted sled, it was suggested that weighted sled towing may increase in propulsive forces generated by the leg musculature and thus increase in stride length. Longitudinal training with weighted vests has been suggested in increase the eccentric strength of the leg extensor muscles during the braking phase of ground contact. Weighted vest training has been linked to increases in muscle and leg spring stiffness, potential decreasing ground-contact time and thus increasing stride rate.

The study concluded that the “effect size statistics suggested small improvements in 18.3 – 54.9m sprint time and average velocity for the non-resisted sprint group, but only trivial improvements for the weighted sled and weighted vest groups. With regard to sprint performance, the results indicate that weighted sleds and weighted vests sprint training had no beneficial effect compared with non-resisted sprinting. In fact for the loads used by the weighted sled and weighted vest groups in this study, non-resisted sprinting may actually be superior for improving sprint performance in the 18.3 to 54.9m sprint interval.

Results:
The weighted sled group had almost no change (.09% improvement in max velocity) and the weighted vest group had a slight change (1.20% improvement in max velocity), while the non-resisted group has the best improvement (2.01% improvement in max velocity).

Over the past 10 years we have made program modifications to our resisted sprint protocols with various sport populations (soccer, volleyball, softball, football, basketball, etc.), and each time we have come up with roughly the same conclusion. The increase in load can force the athlete to make small changes in sprint biomechanics, which ultimately inhibit potential performance improvements.

As in this particular study, we assessed the literature and determined that any load that decreased sprint velocity by more than 10% could potentially cause a negative response to sprint biomechanics and ultimately sprint performance. We have also noticed that you cannot base the loads on body weight alone as some athletes are stronger, taller or more physically mature and this can change how the load affects their speed in this training.

Each time we introduce a new resisted speed training protocol intervention, we come up with the same results. Those in the control group that run in a race type format (sprinting against another player of equal ability) have the best results in max velocity and 20 yd sprint times when compared to those that perform resisted sprints with sleds, resisted treadmills, bands or bungee cords. Here is a study done in the fall of 2010 where 50 subjects performed weighted sprints during the final 6 weeks of a 12 week program, while 50 other subjects performed max speed sprints.

Here’s a thought…

Maybe the body is smarter than we think. And maybe we don’t need to try so hard to ‘mimic’ the sprint exactly. Maybe our goal should be to get the athletes as strong as we can in ‘semi-functional’ activities like box jumps, stair sprints, squatting and lunging activities, and then sprint them in sport specific patterns where the body can learn to apply the newly acquired strength as speed.

Over the last 10 years, the one thing that has worked for us repeatedly without fail is our strength and plyometric program’s effect on sprint and agility performance. We have incorporated loaded sprints using the Woodway Force Treadmill and the Cybex Arc Trainer, but instead of having them run with light loads, we have increased the load significantly, sometimes in excess of 50% body weight. The goal of these sprints is not to increase stride frequency, or even to ‘fool’ the body into thinking it is sprinting, but rather to build dynamic leg strength.

Our philosophy on speed training is as follows:

  1. Move Well… Build confidence, form and rhythm in sport specific movements. Teach the athletes to control their body, control their foot position and posture, while rhythmically moving in athletic patterns. In other words focus on how well you move within the context of your sport.
  2. Move With Speed… Begin to increase the speed of this motion without losing rhythm, form or confidence. Sprint at full speeds, change direction at full speed and jump at maximum height or distance in our plyometric drills.
  3. Increase the Load… Slowly begin to increase the loading patterns of these movements. Medicine ball and dumbbell activities are great for developing athletic jump based or sprint based (hip extension) movements, while also developing deceleration strength, which can potentially improve body control.
  4. Increase Application, Volume and Duration… Put them in situations and drills that allow them to use this newly developed strength and coordination and convert it into athletic movement. Then increase the duration/volume (sets, reps and time) to a point where we begin to condition these movements.

If we follow this progression, we are building better athletes from day 1 by teaching them how to get into positions that allow them to react faster. We are teaching them how to move with intent. Then we strengthen these movements and begin to apply them in more complex situations.

In closing… decreasing the speed of the leg cycle in sprint training settings seems to decrease the leg cycle in full speed drills. In other words, train slow and the body will adapt to the slow training. Train fast and the body will adapt to the fast training.

For more information on our speed training programs check out www.athletefit.com

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