I wanted to follow up one the blog on JB Morin’s Pacey Performance Podcast with a bit more of a discussion around resisted sprints.  This will be a two-part blog.  The first blog will look at the benefits of resisted sled work in developing technical mastery.  This is more an opinion of mine rather than based off lots of scientific research.  The second-part will look at the use of resisted sprints to inform the force-velocity relationship and deduce a more appropriate individualised training programme.

Resisted Sprints in Tennis?

Before we get into the detail let me start off by saying that I am a big proponent of resisted sprints, but not in the context of what we are going to talk about in this discussion.  As you might expect from me (what with my favourite topic now being around the question of how we learn skills) I will make a case that ‘light’ resistance can help with the ‘feeling’ of what good form should feel like.  I find the resistance can feed into your mistake and make it greater so you actually overcompensate and have to produce more force…otherwise you will literally fall over!  The extra effort your muscles are forced to make helps you feel (and therefore learn) what proper movement is.

Implicit learning is when new information is acquired without explicit awareness of the details of the information itself

In the context of Tennis I’m not talking about sleds for acceleration sprints in a straight line.  I use bungee resistance which I have never really quantified in terms of how much velocity drop off it might cause.  But truth be told tennis players are never really getting up to any appreciable speed so I don’t imagine it has major impact on the movement speed.  I just like the fact that in order to stay balanced you have to get your body in the right position, and if you don’t the bungee will not forgive you for it and pull you even further off balance.  The bungee is the ‘coach’ and it gives far greater feedback than I could ever do by ‘telling’ them to get wider and lower!!

I also find the light resistance enables you to repeat the movement several times which is something I took away from the concept of raising anaerobic power in the book ‘Special Strength Training Manual for Coaches.’

We sometimes talk about ex players who might not make great coaches because they ‘Just Do It’ and they may have difficulty in verbalising how they do it, or describing how it should feel etc.  The notion of having talent stems from this idea that they were just born with it, or at least what we can say is that they probably ‘Learnt it ‘Implicitly.’  Implicit learning doesn’t rely on conscious working memory.

The opposite of implicit learning is explicit learning, which is typically how we learn sports skills including running technique (e.g receiving explicit instructions from a coach).  This learning style is a highly conscious process and relies heavily on working memory.

The question then arises, how much resistance is enough to help an athlete feel the ‘correct’ form but not too much that it negatively affects it? In Tennis, as I said earlier, I’m not sure we are talking about enough resistance that it is going to have a significant impact on the kinematics of the movements.

So What About Heavy Sleds?

Academic studies have clearly shown that the determinants of sprinting ability are both the absolute PHYSICAL CAPABILITY of the the body and the TECHNICAL ABILITY to apply this raw capacity in an effective manner.

In the effort to preserve the latter skill, studies featuring resisted sprinting have often used or promoted comparatively light protocols, selected to minimise kinematic alterations to unloaded sprinting technique in both the maximal velocity and acceleration phases (7.5-15.5% decrements in velocity and ~7-20% Body mass).  In the next blog we will discuss how these loads may not provide an effective stimulus for maximising horizontal power production.

However, it is important to say that from the recent scientific studies that have used heavy sleds all the loads used were considered to substantially affect sprinting technique (although this was not actually measured).  From personal communication with JB Morin the question he asked me to consider was

So What? If ACUTE sprinting technique is negatively affected and there are negative adaptations in technical and performance markers, but in the longer term they run faster?

JB Morin in one of his recent articles said that: ”This theory of negative adaptation is largely unsubstantiated.  Furthemore, this notion generally misses the underlying concept of training as a function of the force-velocity relationship.  In the same manner that training in conditions of high velocity may improve velocity capacity, training under significant loading protocols may have a place in the development of high force or early acceleration capabilities (Morin et al. 2017)”

One of the things I took away from reading all the scientific papers was that sprinting against a heavy load (as high as 80% body mass) mimics the first 2-3 steps (or early acceleration of an unloaded sprint).

Heavy Sleds Mimic Acceleration Mechanics

My own experience of accelerating is that it is one of the hardest thing to improve with an athlete that isn’t perhaps strong enough to accelerate with the textbook type mechanics we are looking for.

No amount of cueing is going to help the athlete pull it off.  The benefit I found personally (as an athlete who has never been very strong at the push off) was that being able to push say 60% body mass over 30 metres, I get 30 metres to repeat the same acceleration mechanics that I would normally only experience for one or two steps and with comparatively less time in contact with the ground during actual sprinting.

For me the extra resistance gives my body more time to feel the correct form.  The jury is still out on how this affects sprint kinematics both acutely and chronically but as JB Morin has said, would you rather have done an intervention that keeps a consistent sprint technique with no appreciable change in speed, or have faster athletes who might have altered some of their mechanics? He would rather have faster athletes, and so would I!

Distances as a guide for training

45m unloaded

40m at 20% BM

30m at 40% BM

30m at 60% BM

30m at 80% BM

20m at 100% BM

20m at 120% BM

Applications in Training

To help athletes learn andor improve the skill of accelerating my strategy would focus around resisted sprints using some of the loading guidelines above and a couple of simple cues such as analogies.   I’d also consider periodising the load on the sled starting with a heavier load and slowly reducing it without the athlete’s conscious awareness of it so they can preserve their sprint technique with less and less load.

Analogies and Indirect Instruction

Provide the athlete with one simple biomechanical metaphor that ‘chunks up’ the task relevant (rules) into an individually processed unit of information (such as creating a C shape with the racket when hitting a forehand).  Below are some examples to cue acceleration mechanics using analogies. While providing the athlete with an analogy is explicit in nature, it is ‘cognitively efficient’ – means it requires few attention resources. The idea extends the argument that simple rules are as effective as complex rules for delivering technical instruction.

Marginal Perception

This refers to a gradual change to the stimuli without conscious recognition of the change. In Tennis if a player keeps hitting the net during their serve the traditional approach would be to explicitly inform the player about the biomechanics of the serve.  The  player would most likely improve but they would also be consciously aware of the changes in technique.

An alternative approach would be to be to begin practising with the net at a lower height, thereby allowing the player to serve the ball over the net with greater ease.  Each lesson the coach might increase the height of the net by the smallest margins so that the player is not consciously aware of the change.

My thinking was that you could do the same with the weight of the sled that the athlete is pulling.  Each time they come in you just reduce the amount of weight so that they keep accelerating with a nice technique.

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