Developing Speed

When we think about developing acceleration, or top running speed, additional devices are often included. This may come in the form of weighted vests, sleds, prowlers, parachutes or even using gradients. Whilst it is likely that most interventions will facilitate some improvement in performance, it is also likely that the variables developed by each modality will vary greatly. One only has to visualise the body position during prowler sprints vs sprinting with a parachute to come to the conclusion that each modality is developing a different variable. It may therefore be reasonable to suggest that due to a greater torso angle during sled towing, it may be more favoured to acceleration whereas, during parachute sprinting, providing the chute is attached to the torso, the individual maybe more upright lending itself to developing maximal sprint speed strength.

An excellent paper was published by Cronin et al., (2008) comparing weighted vests and sled towing upon sprint kinematics. The subjects included a variety of male and female sprinters as well as rugby union players. During the repeated measures study, each individual was required to complete 5 maximal sprints over 30m. 30m was a good distance although, potentially, 50m would have been better – 30m allows us to see the initial acceleration phase where the kinematics are significantly different to maximal sprint mechanics seen at 30m plus. Each individual completed a sprint without any modality (base sprint), then a sprint at 15 and 20% bodyweight using the sled and weighted vest. The inclusion of varying loads also provides us with some information regarding the effect of mass on sprint kinematics as well as modality.

Unsuprisingly the base sprints (i.e. unloaded) where significantly faster at the 10m and 30m mark. Likewise the 30m times were significantly slower in both loaded modalities as the resistance increased. When the researchers examined step variables the following key points where established:

• Step length changed during the duration of the sprint (normal acceleration to max speed mechanics)
• Step length was significantly shorter at 20% sled compared to all other loading modalities at all distances measured (5, 15, 25m)
• Step frequency was also shown to be reduced in all loaded conditions compared to base sprint
• Vest sprinting at both loads resulted in a lower torso angle (i.e. more upright than base sprinting)
• Sled sprinting resulted in a greater torso angle (i.e. more forward lean than base sprinting)

As we can see from the paper, subtle changes in sprint training can have significant impacts on kinematic variables. It would seem appropriate to suggest therefore that acceleration maybe better developed using sled devices, which facilitate the greater lean required to generate less breaking forces, whereas top speed running may be better enhanced through loaded vests, which encourages a lower torso angle and therefore application of force below the centre of mass, helping to maintain the velocity developed during acceleration phases.