Biomechanical Aspects of Training for Lifting Heavier Loads and Preventing Injuries

With the West Chester University Ice Hockey team, one of the unilateral strength exercises we do for the posterior chain (hamstrings, glutes, basically, the back of your body) is a Unilateral Barbell Romainian Dead Lift, also referred to as a 1 legged Barbell RDL. Here’s a video of that specific exercise using Dumbbells below from Performance Coach at Endeavor Fitness, Kevin Neeld:

Whenever I teach athletes how to do exercises that involve flexion at the ankles, knees, and hips with the bar or dumbbell in front of the body (ie: deadlift/deadlift variations, cleans and snatches, etc.), a cue I always use is to keep the bar/dumbbell as close to your body as possible. One of my athletes asked exactly why that was the case; hence, this post on Biomechanical Aspects of Training!

Understanding Moment Arms and Mechanical Advantages in Relation to the Body:

To start with, Biomechanics is basically just applying Physics and its theories to the human body and its movements. Let’s use a simple example – everyones’ favorite bicep exercise which is, arguably, no way applicable to hockey/any strength and power sport: The bicep curl.

Although I do not suggest doing bicep curls in the  squat rack (especially while nodding at yourself in a very toolish way), this lifter does demonstrate where you are at your weakest in the range of motion opposed to the strongest.

Individuals talk about weak points in a specific lift all the time – whether it’s a sticking point in a Bench Press or feeling stuck at the bottom of a Squat.  But why are we weaker at certain points than others? The reason is because, in physics terms, your muscle loses mechanical advantage due to the moment arm of resistances’ force getting longer while the moment arm of efforts’ force stays the same. The moment arm of resistance becomes longest when the external load is furthest from the fulcrum. That may or may not sound confusing, so this picture below should explain it better.

Let’s do it this way:

Let the Bicep = Moment Arm of Effort

Let the Hand+External Force (exercise band) = Moment Arm of Resistance

Let the Elbow (more specifically the Lateral Epicondyle) = The Fulcrum (axis at which movement takes place)

Simply, the exercise is hardest when the Moment arm of resistance is longest, which is when the external force is furthest from the fulcrum because gravity is pushing down in a straight line through the external force. As you move the external force in a curvilinear fashion (which is the motion of this specific exercise), either up or down, the straight line (gravity) acting down gets closer to the fulcrum, making the moment arm of effort start to gain mechanical advantage over the moment arm of resistance; hence, the exercise get’s easier.

Bottom line: The exercise is most difficult when the line acting down, gravity, is furthest from the fulcrum. The exercise is easiest when the line activing down, gravity, is closest to the fulcrum.

Relating Moment Arms to Compound Joint Movement Lifts for Increased Performance and Injury Prevention:

Now that we discussed that concept in regards to the bicep curl, let’s use this model to relate to the Dead Lift. Again, let’s do it this way:

Exercise: DeadLift

Let the Prime mover, aka Muscles working (Quads, hamstrings, hips, glutes, etc.) = Moment Arm of Effort

Let the weight = Moment arm of Resistance

Let the hips (bony landmark being Greater Trochanter) = The Fulcrum

If we held the barbell far away from the body, the external load would be further away from the fulcrum (increasing the length of the moment arm of resistance) than it has to be; therefore, making the exercise more difficult than it has to be AND causing negative stress on the low back! If we held the barbell closer to the body, that keeps the moment arm of resistance shorter and allows the muscles working to perform the lift more efficiently. Being more efficient in your form will allow you to lift more weight which will increase your training effect and help you to make more gains.

As a healthy lifestyle note for injury prevention, the common cue for lifting heavy objects – whether it’s a toilet for remodeling a bathroom or carrying a piano up the stairs – people always say to lift with your legs not your back to prevent injury. This is generally true; however, if you bend at the knees to pick up the object but don’t keep the object close to your body, this puts negative stress on your back and can lead to possible injury. So, whether you bend at the knees or hip – or both – is arbitrary. All that matters is that you keep the object as close to your body as possible to keep the negative stress off of your back. If you ever see on a heavy box, “Note: To minimize risk of injury, keep object close to body as possible!” You’ll know why and who suggested it.

Take home message:  It’s important for the athlete/exerciser/performance enhancement coach to know how to decrease the risk of injury and increase their/their athletes’ own performance. When doing a deadlift, clean, snatch, or any other exercise with the barbell or dumbbell in front of you, keep the bar as close to your body as possible. Am I fan of scraping your shins during barbell deadlifts? Ah, it’s not for me (although the moment arm of resistance is shorter doing it that way) because the #1 job of the strength and conditioning coach is to decrease the athletes’ risk of injury! I do not want my athletes leaving the weight room with bloody shins and then putting them in a dirty shin pad for a practice/game and getting some sort of infection; potentially, leading them to missing games. It may look tougher, but science and what works should outweigh what looks tough in the weight room; in fact, that will most likely be what my next post is about. Stay tuned.

Questions? Email me at EKSportPerformance@gmail.com or leave a comment below.

Warm regards,

Eric Keene

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