Monday, 21 July 2014

Should I Use a Weighted Vest to Improve Speed?

Weighted Vest to Improve Short Sprint Speed (Acceleration) or Long Sprint Speed (Maximum Velocity)?
A recent paper by Matt Cross has looked into the effects of a weighted vest on sprint kinetics (forces) and kinematics (motions).

Why the use of a Weighted Vest?
A weighted vest while sprinting is commonly used to overload the neuromuscular system which could potentially elicit positive effects on ground contact time, flight time, step length and step frequency. Therefore, this can increase the athlete’s ability to generate vertical and horizontal forces.  This can potentially translate into greater force production and better sprint performance (i.e. faster) when the vest is removed.

How heavy?
In this paper, a 9kg vest and an 18kg vest sprint was run as well as a baseline (no vest) sprint on a non-motorised treadmill. This translates to roughly 7% and 20% of body mass of the subjects which falls in line with previous literature. Thirteen sport active university athletes took part (rugby, hockey, track sprint, weightlifting)

How did loading affect motion (compared to baseline)?
       Step frequency remained similar between all conditions while step length significantly decreased in loading conditions.
       Peak velocity significantly decreased in both loaded conditions.

How did loading affect Acceleration (compared to baseline)?                                                            No significant effect on peak ground reaction force (vertical forces; GRF), horizontal force, power output  with either load.
       Ground contact time remained unchanged.
       18kg vest flight time significantly decreased.

What about Max Velocity (compared to baseline)                                                                         Only with 18kg vest did peak vertical force significantly increase.
       No significant effect on horizontal force.
      Significantly lower power output during 18kg vest sprint.
       Significant increase in ground contact time.
       Both loading conditions resulted in significant decreases in flight time.

Interesting Findings?
                At max velocity, only the 18kg vest showed moderate increases in GRF meaning heavier loads may be needed in order to promote greater GRF production. Peak GRF did not significantly increase during the acceleration phase at any loading protocol meaning it seems that additional mass to the athlete does not result in increased GRF. This could be explained by the additional load affecting the rise and fall of the centre of mass (COM) during the flight phase (i.e. decrease in flight time). If flight height during the acceleration phase decreases, this means there will be a resultant decrease in GRF.

Vest loading had no significant effects on horizontal force and power. It appears vest loading affected the athlete’s ability to produce force in the horizontal direction through not being able to effectively control the additional mass.

So Should I Use a Weighted Vest To Get Faster?
It seems a weighted vest is not an effective way to improve acceleration (short sprint speed) as GRF, horizontal force and power were not significantly affected. A greater load may be needed to overload GRF and power during maximum velocity but greater loads can potentially elicit negative changes to sprint kinematics.

Based on this paper, I would not recommend using a weighted vest to improve short sprint speed or long sprint speed due to the weighted conditions not overloading important factors to improving speed (i.e. horizontal force and power, GRF). Further posts will give my recommendations J


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