Swing Phase Mechanics during Sprinting….higher level discussion

Posted In: The Classics

  • Mike Young
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    Mike Young on #10473

    I was thinking about the recent discussion on sprint start mechanics and came up with some ideas I thought I’d throw out. When examining the swing phase of sprinting acceleration their is some debate over whether it is more beneficial to step over the opposite knee during early acceleration or move the legs through a piston like motion during the swing phase. As I discussed in the linked thread above, I’m a proponent of the piston like motion early on during acceleration with a gradual shift toward a stepping-over motion as an athlete approaches top-end speed. While I stated some of my reasonings for this thinking in the thread above I was giving some thought as to the etiology of the shift from piston to stepping over swing leg mechanics. It occurred to me that the motion should be dictated by the athlete’s velocity. At first glance this may seem intuitive and overly obvious for those who have the same thoughts (starting with piston like motion and gradually moving to a stepping over action) on leg swing as me. It is however slightly more complex than might meet the eye. The following examines the etiology of this relationship (as I see it).

    In technically efficient sprinting the degree of stepping over should be dictated by the velocity differential of the athlete’s foot at ground contact and the athlete’s body at ground contact. At ground contact, the velocity of the foot is zero but the athlete’s body continues to move. During early acceleration, this differential is relatively small. With each step however, the differential gets larger and larger. The greater the velocity of the athlete’s body at ground contact, the greater they will be moving relative to their foot at ground contact. When the athlete is running at or near top-end speed this differential is at it’s highest. Because of this, and the limited ability of an athlete to apply force within a short period of time, the velocity of the run should dictate the actions of the swing leg. That is, a person needs a given amount of time to apply force to the ground throughout the course of a run (ground contact time). While this time will gradually decrease with each step during a sprint acceleration to top-end speed, it will not decrease at an equivalent rate as the athlete’s forward velocity will increase. Because of this, the athlete’s body is moving faster and faster while their foot is on the ground for roughly (for the purpose of this discussion) the same amount of time. As a result, as a person accelerates their body will be moving forward more relative to their support foot with each step. Early on in acceleration, the differential between foot velocity at ground contact (zero) and the body’s velocity with respect to the ground / foot is relatively low and as a result a piston like motion is not only possible but beneficial. It is beneficial because it makes it easy for an athlete to attack the ground with the appropriate shin angles and finish their push-off with their feet well behind their hips which is critically important during acceleration. At higher speeds, while athlete’s should probably try to attack the ground with a similar piston like motion (with their body more upright of course!) to attack the ground with a vertical shin position so that they can increase vertical ground reaction forces, the higher foot:body velocity differential at ground contact will mean that at toe off the body will be will be far ahead of the body and stepping over (which shortens levers and allows a faster swing phase) will be required to allow an athlete to get back into correct position to attack the ground with a vertical shin position for the subsequent ground contact.

    So in summary, it may be beneficial for an athlete attack the ground with a piston like motion at any speed because it allows an athlete to make ground contact with the desired shin angles. At higher velocities however, the body will be moving so fast relative to the foot that it will require the athlete to step-over the opposite knee so that they can get the leg back into a piston like position for ground contact. At lower velocities, such as early on in acceleration, the stepping-over action is not necessary because the differential between foot and body velocity at ground contact is small and the stepping over action may even make having the desired shin angles at ground contact more difficult.

    What does this mean as far as coaching and cueing in the sprints? I’m not quite sure yet but it never hurts to understand the mechanisms of why we should have someone do something. Thoughts?

    ELITETRACK Founder

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    coachformerlyknownas on #42484

    Very interesting points. One of my athletes has been working hard at the process of overcoming inertia from the blocks and acquiring force to accelerate from 5-10m out. It can be shown that the foot is landing slightly ahead of the hips and this athlete’s level of strength is possibly too low to compensate.

    Would the piston-like action mentioned require more emphasis to drive the knees “up” or simply continue to develop greater strength levels to increase the rebound effect? In addition, would body position require less or greater forward emphasis to maintain a small differential between foot and body velocity at ground contact during block clearance? And what, if any, change occurs with arm swing during the transition phase – aligning with the change in lower body swing action?

    Mike Young
    Keymaster
    Mike Young on #42485

    [i]Originally posted by Price[/i]Would the piston-like action mentioned require more emphasis to drive the knees “up” or simply continue to develop greater strength levels to increase the rebound effect?

    I think it’s probably a combination of the two. I would mention however that much of her problems would be solved with less body lean. She doesn’t yet have the strength/power to create the flight necessary when departure and push-off angles are so low early on in the run.

    In addition, would body position require less or greater forward emphasis to maintain a small differential between foot and body velocity at ground contact during block clearance?

    I don’t understand your question. Please clarify.

    And what, if any, change occurs with arm swing during the transition phase – aligning with the change in lower body swing action?

    Arm swing movement amplitude (especially at the the elbow) should get smaller as the athlete progresses to an upright position.

    ELITETRACK Founder

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    jjh999 on #42486

    (…back from the dead…)

    Nice topic for discussion, Mike. My $0.02:

    I think that the “piston” and “cyclical/stepover” cues both have pluses and minuses.

    The “piston” cue can be very beneficial for the athlete to visualize and perform vertical force production once the acceleration phase is completed. One drawback, however, could be the athletes overemphasizing the “upstroke” portion of the piston-like movement and adopting a posterior lean at the waist (kinda like a drum major) in order to drive the knee up as much as possible.

    The “cyclical/stepover” cue can be excellent for max velocity mechanics, but I think it is imperative that along with that cue, that the coach emphasize that the foot needs to come straight up to the glutes and “letting the knee lead”. Otherwise the athlete may feel like they are stepping over, but doing it while spending way too much time in the backside.

    From a practical standpoint, I’ve predominantly used the “stepover” once I have cleaned up the backside mechanics to a point that I can tolerate. However, some athletes tend to get too long at the end of a 100m dash and in that instance, may use the “piston” cue in order to preserve a decent ground contact position with respect to the COM.

    Thoughts?

    Mike Young
    Keymaster
    Mike Young on #42487

    [i]Originally posted by JJ[/i]
    The “cyclical/stepover” cue can be excellent for max velocity mechanics, but I think it is imperative that along with that cue, that the coach emphasize that the foot needs to come straight up to the glutes and “letting the knee lead”. Otherwise the athlete may feel like they are stepping over, but doing it while spending way too much time in the backside.

    Agreed. In reality, I think that an athlete should probably be attacking the ground in a piston like manner but because the differential in speed of their body with respect to their foot at support is so great, the foot will fall behind the body at midstance-toeoff. This is especially the case in athletes that aren’t super powerful.

    From a practical standpoint, I’ve predominantly used the “stepover” once I have cleaned up the backside mechanics to a point that I can tolerate. However, some athletes tend to get too long at the end of a 100m dash and in that instance, may use the “piston” cue in order to preserve a decent ground contact position with respect to the COM.

    Thoughts?

    I’ve actually found out the same thing. One of my athletes has excessive posterior mechanics and the stepping over the knee cue never seems to get the right response. I’ve found that using “push up,” “get off the ground quicker,” and “imagine there is an elastic band attached from your glute to your heel.” I can’t take credit for the last one. Someone far smarter than me thought that one up.

    ELITETRACK Founder

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    coachformerlyknownas on #42488

    [i]Originally posted by JJ[/i]
    (…back from the dead…)… I’ve predominantly used the “stepover” once I have cleaned up the backside mechanics to a point that I can tolerate…

    With this in mind, should rotary running sessions, similar to that of Frye, Carson, et al, be a regular activity during general and specific work phases?

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    jjh999 on #42489

    [i]Originally posted by Price[/i]
    [quote][i]Originally posted by JJ[/i]
    (…back from the dead…)… I’ve predominantly used the “stepover” once I have cleaned up the backside mechanics to a point that I can tolerate…

    With this in mind, should rotary running sessions, similar to that of Frye, Carson, et al, be a regular activity during general and specific work phases? [/quote]

    (Please note, Price, this is not directed at you):

    I know that this is probably blasphemous, but I don’t believe in “Rotary Running”. I believe in correct and efficient biomechanics. I don’t believe in gimmicks and jargon.

    Mike Young
    Keymaster
    Mike Young on #42490

    [i]Originally posted by JJ[/i]I don’t believe in gimmicks and jargon.

    This may very well be grounds for removal of your moderator status. :spin:

    ELITETRACK Founder

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    QUIKAZHELL on #42491

    Now that I think about it this may be a problem one of my athletes is having. It seems that her ground contact times are way to long and she sounds real heavy each time her spike hits the track. Im think now if we clean up her backside mechanics which I never really noticed or for that matter had a look at maybe things will improve. I will try the 2 cues mike had mentioned. It seems as her stride frequency is not very good but maybe it is due to backside mechanics. The cues I have been trying to use in reguards of improving her frequency with not much sucess has been "get off the ground quick" and make believe you are running over eggs and each time you step down and crush the egg shells you dont want the egg sticking to your feet"
    thoughts.
    I may get some video of her on here in the next few days.

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    Todd Lane on #42492

    Was cleaning up some folders last night and came across some notes from Vince Anderson presentations several years ago a Level III.

    Coach Anderson's point on sprint mechanics, was that "good sprinting looks rotational, but should feel like marching".  His rotational comment refering to the backside of stepping over the knee and the front side looking like that presented by the mustached gurus of, $$$ videos of the mid 90's.

    Cues and feelings being different than looks…

    Don't know if that adds anything to above discussion.

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    tony on #42493

    The muscle groups being utilyzed and relied upon predominantly during these two phases of the sprint race may dictate the type of cue you wish to use.  As you pointed out Mike,

    "It is beneficial because it makes it easy for an athlete to attack the ground with the appropriate shin angles and finish their push-off with their feet well behind their hips which is critically important during acceleration. At higher speeds, while athlete's should probably try to attack the ground with a similar piston like motion (with their body more upright of course!) to attack the ground with a vertical shin position so that they can increase vertical ground reaction forces, the higher foot:body velocity differential at ground contact will mean that at toe off the body will be will be far ahead of the body and stepping over (which shortens levers and allows a faster swing phase) will be required to allow an athlete to get back into correct position to attack the ground with a vertical shin position for the subsequent ground contact."

    During the accleration phase we tend to use our quad groups more predominanetly than our hamstring groups.  The Quad group is much stronger and can generate a great deal more force than can the hamstring group and hence the cues that seem most helpful would tend towards the piston action with the lower heel recovery and larger amplitude arm drive.  The problem is that quads are slow in the neural recruitment and firing sequence.  The hamstrings however, are the fastest firing muslce in the body so as the athlete makes gains in velocity it is natural to transition to a more cyclical and hamstring dominated process.  Hence our more cyclical cues. I find that athletes who transition too early tend to burn out in the late stages of the race (Surin in his early career), and athletes who continue to attack the ground in a quad dominated drive never really get up to speed and are passed early on as other competitiors make the transition. 

    I am very much a proponent of an active foot on touch down and the piston cues later in the race tend to lead towards a more vertically inclined ground attack increasing the oscillation in the COM. Over striding in the later stages tends to come into effect when the hamstring is tired and the athlete lowers their COM to utilyze more of the quad grouping.  I prefer to cue them as to staying tall and engaged through the hips to allow the cyclical motion to continue without thinking about it too much.  I also cue them to concentrate on a good fast elbow drive from the high position down to keep the shoulders relaxed and the turn over quick.

    Let me know what you think

    Mike Young
    Keymaster
    Mike Young on #42494

    Tony-
    Welcome to the board. Nice post. What do you mean by active foot contact? Negative foot speed relative to the COM? If so, do you cue this directly or through indirect means.

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    tony on #42495

    Sorry about the delay in getting back to you Mike, I've been away for the past couple of weeks.

    I do mean negative foot speed relative to COM.  I view it as a natural process due to good posture and excellent recovery back side mechanics to efficient front side mechanics.  To my way of thinking, as the free leg recovers and swings forward to a high knee position you are creating the potential for a good active release and "active" foot contact.  So my cues tend to be indirect for most athletes — upon staying tall and keeping the heel tucked until release.  The only direct cue I use for late race fatigue resulting in a longer than desired foot contact is "fast foot".  Indirectly in a race I would cue the arms or posture "quick arms", or "stay tall", or "stay over" for those who tend to get into a negative trunk position.  In practice cues depend upon the athlete's ability to put into action what I am looking for.  Some direct, some indirect and a great deal of individual questioning.  I often find that it comes down to some physical problem such as inflexibility, muscle imablance or incorrect sequencing so in corecting the problem I find and add drills or sequences that allow the athlete to search for the feeling that provides the most efficient action. 

    Sorry, it does not seem like a clear answer to your question — I guess in short, how I cue it depends upon what is producing it.

    All the best,

    Tony

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    purebreeze on #42496

    I this is late,but I wanted to give some thoughts. I had a chance to work with Dennis Mitchell a couple months back and he used both the piston motion and stepping over in his sprinting approach. He would take the drive phase and explain to the athletes that it should be like a car pumping its pistons and then athlete should transition into stepping over for max velocity.

    Mike Young
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    Mike Young on #42497

    I this is late,but I wanted to give some thoughts. I had a chance to work with Dennis Mitchell a couple months back and he used both the piston motion and stepping over in his sprinting approach. He would take the drive phase and explain to the athletes that it should be like a car pumping its pistons and then athlete should transition into stepping over for max velocity.

    This is how I teach it to most of my athletes. The question however is how much the stepping over should be coached or is the movement actually a pistol movement that is occuring when the body (relative to the ground) is moving at a much greater rate thus resulting in a leg that travels further behind the hip and an accompanying elastic response that causes the hip to flex violently and in so doing cause the heel to tuck up under the butt and step over the knee……I don't have an answer….just posing a question. I think in most cases, cueing the stepping over action is definitely important but this seems to not be necessary in all cases and it may be a case of what is going on is actually more reflexive than previously thought.

    ELITETRACK Founder

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