Progression in training is one of the cornerstones of improving performance in athletics, but it isn’t always easy to achieve. Athletes have used a countless number of tools and methods over the years to improve performance. In a recent study in the Journal of Strength and Conditioning Research, one such tool, the weight vest, was analyzed as a way to improve sprinting.
In some sports, like weight lifting, progression is easy enough to understand. Lift more weights for more sets and more reps than you used to. Easier said than done, for sure, but simple enough. In sprinting performance, a progression is just as simple – you just run faster. But actually achieving this progression is a completely different animal. In fact, speed improvement over short distances is perhaps one of the most elusive goals in fitness.
Since increasing the resistance is one way to induce progression, several methods are commonly employed for sprinting, but their benefit is sometimes controversial. For example, some athletes use parachutes, which make wind resistance a greater factor than usual. In today’s study, the researchers were concerned with the use of weight vests. Unlike many tools, a weight vest is easy to measure progressively and easy enough to employ.
The researchers were concerned with the effects of vests of two different weights on sprinting. The participants ran either with no vest or with a vest that weighed either 19.8lbs or 39.6lbs. The researchers were concerned primarily with the kinetics (force) and kinematics (motion) of using a weighted vest. This means they didn’t look at speed increasesover time, but at what actually occurs in a single sprinting session when you don a vest.
Let’s start by discussing the most obvious results. Horizontal force outputoverall was not changed by the vest. In other words, although it takes more horizontal effort to run with a vest on, it also slows you down. The relationship is linear with the weights they used in this study, so the average force output was unchanged. This result makes a lot of sense. Unlike the aforementioned parachute, the vest applies resistance in the vertical vector because it works with gravity, so the horizontal effect was insignificant.
The vertical realm is where we get perhaps some surprises. Similar to the horizontal forces, there were no changes in peak vertical forces. After analyzing the motion changes in the sprint, the researchers discovered that the athletes had reduced “flight times,” which means they spent more time with their feet on the floor because of the weight. This effect greatly reduced the peak forces that resulted from landing, which pretty much evened out the peak vertical forces. Only the 39.6lb vest caused an increase in average vertical forces. This result indicates that if an increase in vertical force output is a goal for a sprinter, he or she might only benefit from a vest that is heavier than normally recommended.
While a heavy vest is needed to improve vertical forces, we also need to consider the value of doing so. Any time an external load is applied to a technical movement like a sprint, the technique also changes, as seen in the kinematic differences during this study. This is why pitchers in baseball often avoid weighted balls, as their pitching velocity with a normal ball is ultimately reduced, which defeats the point. While a heavy vest might be an important method of progression for a sprinter, coaches should also dedicate ample time to keeping form sharp.
References:
1. Matt Cross, et. al., “Effects of Vest Loading on Sprint Kinetics and Kinematics,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000354
Photo courtesy of CrossFit Impulse.