Even Small changes in rate of force can affect sprinting ability. A decrease of .005s in ground contact time over 20 foot strikes would decrease sprint time by .1s
Then it goes on to say Significant correlations between maximal force development in concentric squat one rep max and 100m time have been demonstrated.
Any thoughts on this statement people??? This sound right? higher the squat the higher force development thus decreasing 100m time.
Also it talks about leg press offering a higher outcome in sprinting ability over squat Squat a 2.3% decrease in 100 m time and a leg press 3.6% decrease in time.
This article validates what many on here have been saying for some time…use all the tools and means available. I have always believed that the squat, Oly lifts, jump squats, steep hill sprints and plyos have a place in the training program of anyone who wants to improve the explosive strength and quickness.
Z. Lee (Winning 22) - 22 April 2009 02:55 PM
...A decrease of .005s in ground contact time over 20 foot strikes would decrease sprint time by .1s.
Reducing GCT does not make you faster…running faster reduces GCT. This may seem like knitpicking, but I think an important distinction needs to be made in terms of cause and effect, as the interpretation has important bearing on the means chosen to improve performance.
Does Rate of Force development not impact on contact time though? I would have thought a greater RFD would have negated the need for a longer CT. That would hence cause an increase in stride length, potentially increasing running velocity.
So my point is basically that running faster does not reduce CT, but greater RFD reduces CT, causing you to run faster, therby decreasing CT. Im happy to concede im wrong, just trying to further the discussion abit more.
Actually, ive worded that badly. What I mean is that running faster doesnt decrease CT, producing a set amount of force quicker reduces CT, therefore allowing you to run quicker.
Actually, ive worded that badly. What I mean is that running faster doesnt decrease CT, producing a set amount of force quicker reduces CT, therefore allowing you to run quicker.
I would agree with this statement. The force comes first, however. Seeking shorter GCT, through special exercises that don’t do anything for improving RFD, shouldn’t be a specific means in training. Seek to develop greater power, and to be able to express it maximally in the shortest time possible. The GCT, and hopefully the speed, will follow.
It’s really an interesting discussion. The force has to come first BUT you won’t continue to see shorter and shorter GCTs unless the body is moving very fast and the leg is ‘springy’ enough to get on and off the ground very quickly. Both have to be present. For example, if you take the same sprinter and measure GCTs during acceleration they are fairly long compared to at top speed. There RFD capacities haven’t changed but the rate that their body is moving with respect to the groun has.
The higher the running speed, the higher the horizontal backward velocity of the foot during ground contact has to be to be able to increase running speed. Faster foot speed equals shorter ground contact time.
Rate of force development is one factor that will influence foot speed. Note that the onset of this force (relevant for horizontal foot speed) begins long before ground contact time. (Onset of force = onset of deceleration of the free forward swinging leg.)
There is also the vertical force component though.
The higher the running speed, the higher the horizontal backward velocity of the foot during ground contact has to be to be able to increase running speed. Faster foot speed equals shorter ground contact time.
Rate of force development is one factor that will influence foot speed. Note that the onset of this force (relevant for horizontal foot speed) begins long before ground contact time. (Onset of force = onset of deceleration of the free forward swinging leg.)
There is also the vertical force component though.
Well said. So, again, focus on the factors that improve running speed and force development, and GCT will take care of itself…no need to ever focus training on specifically reducing GCT…would you agree?
The way I look at training this aspect is to focus on force production, such as plyos and weight training. By improving the neural pathways, you will automatically increase RFD. Add into this tendon stiffness which occurs via sprinting anyway, and RFD will improve, with a reduction in GCT.
As with everything, its a complex mix to get an improvement which can be easily overthought, but sprint coaches have for years being doing weights/plyos without any real emphasis on GCT, which has been more of a by-product.
It’s really an interesting discussion. The force has to come first BUT you won’t continue to see shorter and shorter GCTs unless the body is moving very fast and the leg is ‘springy’ enough to get on and off the ground very quickly. Both have to be present. For example, if you take the same sprinter and measure GCTs during acceleration they are fairly long compared to at top speed. There RFD capacities haven’t changed but the rate that their body is moving with respect to the groun has.
Ive been mulling over this for a while. The way I have looked at it is like so:
* At top speed, the body is already moving, so no real inertia has to be overcome. I want to liken it to being in equilibrium, where so long as no negative force is produced, the body will keep moving forwards. Obviously, this is an over-simplification, but Im using it to illustrate my point. So, as its in “equilibrium”, less force needs to be produced, negating the need for a longer GCT. In addition to this, the foot strikes more or less under the body, so cant be in contact with the floor for too long.
* Whilst accelerating, the body has to overcome initial inertia in order to get to top speed. This requires more force, hence the longer GCT. Also, the foot has to come out in front of the body, in order to overcome the forwards lean of the athlete. This causes the foot to be in contact with the floor for longer.
One way to instantly disprove my theory would be to quote GRFs at acceleration and max speed, which would probably be similar, possibly putting more emphasis on my comments about foot placement.
Finally, Im not a biomechanist, and you are, so really this is just me thinking out loud to try and further the discussion!
Well said. So, again, focus on the factors that improve running speed and force development, and GCT will take care of itself…no need to ever focus training on specifically reducing GCT…would you agree?
I definitely don’t subscribe to the notion that technique does not matter. Execution of the free leg swing is highly adjustable and will effect horizontal speed and therefore ground contact time. However, I certainly would not recommend trying to shorten ground contact time through a premature toe-off!
* At top speed, the body is already moving, so no real inertia has to be overcome. I want to liken it to being in equilibrium, where so long as no negative force is produced, the body will keep moving forwards. Obviously, this is an over-simplification, but Im using it to illustrate my point. So, as its in “equilibrium”, less force needs to be produced, negating the need for a longer GCT. In addition to this, the foot strikes more or less under the body, so cant be in contact with the floor for too long.
* Whilst accelerating, the body has to overcome initial inertia in order to get to top speed. This requires more force, hence the longer GCT. Also, the foot has to come out in front of the body, in order to overcome the forwards lean of the athlete. This causes the foot to be in contact with the floor for longer.
In a way, GCT is fixed by leg length. As one runs faster, there is less time in which the foot can remain in contact with the ground. However, some very strong runners (typically seen in rugby players) can run at maximum with a distinct bend in the knee and a bit more external rotation of the hip, and therefore can remain in contact with the ground for longer but will plateau in speed fairly quickly. It must be realised that fundamental to elite sprint performance is the ability to produce force in short GCT’s. Murphy et al. (2003) measured a significant difference (p=0.01) with faster runners spending 0.02s less on the ground each step within the first few steps of early acceleration.
Faster sprinters are able to produce more force in less time in all phases of sprinting (Mero et al. 1992 is the best source). What is more important force or GCT? At maximal velocity, maximal force correlates very poorly (-0.38 horizontal, -0.08 vertical), grabbing velocity of the foot (-0.12), and GCT still not very impressive at -0.43 although this will vary according to leg length. What correlates greatest is force impulse (-0.96 braking, 0.90 propulsive) and… angular velocity of the thigh (0.91). This emphasises my first ever post to on this website that whilst there is very little difference in maximal squat (or deadlift, or Olympic lift), there is a massive difference between sprinter who can run at 10.82m/s (angular velocity of the thigh 550deg/sec) and Donovan Bailey 11.14m/s (angular velocity of the thigh 953deg/s)(source Derek Kivi 1999). Angular velocity of the thigh is related to GCT (-0.75)and total force impulse (0.92). How does one move one’s thigh faster? I’ve attached a page that may help. Force-time specficity is the category we need to accept.
The study in this discussion is very summarised (i.e. 5 pages instead of 25) and one must caution with regards to figures in the absence of control data and absence of other studies of similar training modalities. Suffice to say, plyometric training does reduce GCT by 0.006-0.007s (Rimmer and Sievert 2000). As stated in the original article but expanded here, if one saves 0.0065s per step for 45 steps that equates to 0.29s saved over 45 steps (equal to the improvement in performance - Delecluse 1995 also mentioned in the article of this post). However, plyometric training has not evolved for many decades so further improvements to sprint performance are beckoning.
In light of last 2 posts…Jeremy, do you believe that the recovery of the support leg should be active to minimize ground contact time and backside mechanics?
In light of last 2 posts…Jeremy, do you believe that the recovery of the support leg should be active to minimize ground contact time and backside mechanics?
Getting a bit technical for me. Do you mean that the sprinter should aim to pick the heel up quickly which would avoid extension of the knee/prolonged ground contact?
My feeling on what I have written just above is that such a recovery of the leg should primarily be a consequence of good technique (and cleverly designed strength training - oops…explosive type strength training) and/or high velocity low force limb training. When reading through a previous (and often humorous) discussion with the Bear-powered group I noticed the use of the words ‘inverted pendulum’ and other similar words by members of this community. Another previous discussion on Gatlin’s mechanics brought up the fact that he was inefficient and generated too much braking force. However, I contend that the geographical placement of the foot ahead of the centre of gravity masks the positive effects of the dynamically moving pendulum (i.e. the backward swinging leg) in this area. It would be great for Dr. Mann to share his data with us but for now I’m working with data from Coh et al. where force impulse in the braking phase correlates extremely highly (0.96) with maximum velocity. Just out of interest the force impulse in the propulsive phase is 0.90 (also extremely highly correlated).
In fact as I have always stated, Flo-Jo is the ultimate example of the mechanics required to create positive effects within the traditional area known as the braking phase. Is it no surprise as to the magnitude of her legacy?
