Biomechanics of Sprinting

This is probably not the right forum, but I wasn’t sure where else to post.

I’ve been reading through Essentials of Strength Training and Conditioning. Chapter 17, which is Speed, Agility, and Speed-Endurance Development, has got to be the most poorly-written chapter that I’ve ever seen. In any case, there is a section on the Fundamental Movements Occuring in Maximal Velocity Sprinting, and it’s a little more than confusing. I was hoping that someone might be able to help me understand the biomechanics aspect.

I’ve attached a compilation of the picture and the associated phases. I guess you could say that most of them seem confusing, but I’ll highlight a few to start:

  1. In “Early Flight”, how does eccentric hip flexion decelerate backward rotation of the thigh?
  2. Again, in “Early Flight”, how does eccentric knee extension decelerate backward rotation of leg/foot?

Many thanks for any help.

That is confusing.

If I understand correctly, during “Early Flight” the forward leg is raising up and extending. The eccentric hip flexion slows down the forward rotation of the hip, and the eccentric knee extension slows down the forward rotation of the lower-leg.

But that’s horribly written.

Yes, that’s also what I was thinking. I couldn’t figure out how hip flexion would at all decelerate the thigh. I think they’re supposed to be talking about the recovery leg, but sometimes it doesn’t seem like it at all if you look at the other stages.

In general I would say that this is a decent book that’s easy to follow, but this chapter stinks.

“eccentric hip flexion decelerate backward rotation of the thigh”

Think about it like this, the glute is extending the hip in a concentric fashion during the driving portion of the sprint while it’s antagonist, the hip flexors are lengthening as the glute contracts. This happens in basically every single joint action we make be it a bicep curl or squat. In order for the joint to remain intact (read not snapping your femur out of the socket) the antagonist muscles need to act in a decelerative manner while the agonist is contracting.

As for the second one, it’s too early for me to figure that one out right now haha

But what you’re describing “glute extending the hip and hip flexors lengthening” is hip extension, not hip flexion. That’s the part that I don’t get. The only thing that I can think of is that the whole picture/description is wrong. I searched for book errata but didn’t find any. If they’re aware of the error, they’re not letting on.

Concentric hip extension is also eccentric hip flexion, are you studying for the test?

How can that be? Flexion describes a completely different movement than extension, doesn’t it? I mean, the same muscles can do both extension and flexion (for example, the hamstrings can do eccentric hip flexion and concentric hip extension) but I don’t think concentric hip extension is the same as eccentric hip flexion.

Sorry about that, I should have said that according to the illipsoas that the action is the same, but you are correct with your hamstring example. I hope that cleared things up a little bit, it took me a while to figure out NSCA’s way of describing things. They seem to make mountains out of molehills but it’s still good practice to understand the language especially if you’re testing for a cert.

Yes, I’ve been trying to spot the things that the NSCA will be most likely to test. The practice exams give some good examples, but I know that there will always be things to trip me up. (Like the sprinting analysis above!)