A Starting Strength Coach (SSC) needs to be able to integrate the fundamental principles upon which the model is based, i.e., Mechanics (Physics), Anatomy, and Physiology.

Being able to take the complex details of the Starting Strength model and translate them into simple arguments shows that you understand the model. Your own understanding and integration of these principles will enable you to have informative and accurate discussions with clients, medical professionals, and personal trainers. Note, you will have to tailor your language to what your audience can hear and understand.

Integrating what may seem like disparate concepts (e.g., mechanics and physiology) into your understanding of the Starting Strength model may seem a little daunting at the beginning of your coaching development. To help you, I would like to give you a M.A.P. to the model.

• Mechanics: Where forces are applied to the levers of the skeleton, and the magnitude of those forces.

• Anatomy: What muscles can collectively respond to the imposed force at each location

• Physiology: How well those collective muscles can respond to the imposed force at each location

Here’s a brief description of what each might include, then we’ll finish with a simple example of how to implement this framework.

Mechanics

• Effect of gravity on the bar, imposing forces on the body

• Types of forces - compression, tension, moment, compression + moment, tension + moment

• Moment arms and joint angles - how the force (the load on the bar) is multiplied along a segment and/or around a particular joint

• COM/CCOM - center of mass and combined center of mass - maintaining the CCOM over the center of balance to avoid unnecessary moment arms

Anatomy

• Muscle origins and insertions

  For example, while the muscle bellies for the quads, hamstrings and gastrocs are some distance from the knee (the knee joint is not, after all, a bulging mass of muscle), we describe these muscles as being the mass that operates the knee joint because the tendons that attach those muscle bellies to the skeleton cross the knee joint.

• Where around the joint is the muscle belly located (anterior, posterior, medial, lateral, superior, inferior)

• What effect does the muscle have on the joint movement when it contracts (open, close, flex, extend, abduct, adduct)

Physiology

• Muscle belly length, as compared to resting length, and the effect on contractile force production

• Inclusion of a Stretch Reflex in the design and performance of the movement pattern, that contributes to the muscle force production

An Example: The Barbell Curl

Here's a simple example. Let's talk about every Bro's favorite exercise, the barbell curl (done in the squat rack, obviously).

Mechanics: The load is held in the hands and the joint around which force is imposed by the load is the elbow (let's assume that you are keeping your wrists straight). Forces around the shoulder joint come into play near the end of the rep. The magnitude of the forces imposed by the load depends on where you are in the rep.

Anatomy: Let’s keep it simple and just discuss the biceps as a proxy for all the muscles that cross the elbow joint and contract to lift the load. Contraction of the “biceps” closes the elbow joint angle.

Physiology: Since the biceps are on the anterior side of the humerus, and the joint angle changes from fully open to fully closed during the concentric portion of the rep, the biceps continually shorten. At the start of the rep, the biceps are fully stretched out and can produce minimal contractile force. During the rep, the bicep muscle bellies first shorten to resting length, where they can produce maximum contractile force production, and then are fully shortened at the top of the rep, where minimal contractile force can be produced.

Now that we understand the basic framework of the barbell curl, let’s discuss what happens as a function of joint angle during the rep (Figure 1).

Bottom of the rep (Elbow flexion of 0º): The load hanging from the hands imposes tension down the length of the humerus and ulna/radius. There is no external moment arm between the load in the hand and the elbow, so the force of the load is not multiplied. The biceps have limited contractile force production.

First 1/4 of the rep (Elbow flexion of 45º): As you start to lift the barbell, the external moment arm between the load in the hand (the gravitational force vector is vertical) and the elbow joint begins to increase. This makes the load feel heavier, and changes the force down the ulna/radius from pure tension to a combination of tension plus moment. There is moment around the elbow joint, trying to extend the elbow. The humerus is still under tension. The biceps that cross the elbow joint begin to shorten, increasing the force production of the muscle belly as it gets closer to resting length.

Halfway up (Elbow flexion of 90º): The external moment arm between the load and the elbow is now at a maximum, as is the magnitude of the force imposed by the load on the levers of the arm. The force applied to the forearm is pure moment, with the moment around the elbow joint still trying to extend the elbow. The humerus is still under tension. The biceps that cross the elbow joint continue to shorten, reducing the amount of contractile force that can be applied to the load.

Limit of Elbow Flexion (Elbow flexion of ~150º): As you move past the halfway point, the external moment arm between the load in the hands and the elbow joint begins to decrease. This makes the load feel lighter, and changes the force down the forearm from pure moment to a combination of compression plus moment. There is still moment around the elbow joint, trying to extend the elbow. The biceps are fully shortened distally, and cannot flex the elbow any further.

Finishing the rep (Elbow flexion of ~150º + shoulder flexion): So far, we’ve worked the distal function of the biceps, namely elbow flexion. Since elbow flexion is limited to about 150º, the proximal function of the biceps, notably shoulder flexion, is used to get the bar close to the shoulders at the top of the rep (along with considerable contribution from the anterior portion of the deltoids). The elbows sweep forward under the bar, as the bar travels back towards the shoulders. The force down the forearm is a combination of compression plus moment, and the moment around the elbow joint is now trying to flex the elbow. The humerus is under a combination of tension plus moment, and there is now an external moment arm between the load in the hands and the shoulder joint. The moment around the shoulder joint tries to extend the shoulder.

Congratulations, you’ve completed the concentric portion of the barbell curl. As you lower the bar back down, these same forces and moment arms are applied to your skeletal/muscular system, but now the biceps muscles are eccentrically contracting to lower the weight under control.

Internal Moment Arms

To this point, we’ve discussed the external forces on the levers of the skeleton. External moment arms multiply the force of the load.

To lift the load, the externally imposed forces must be counteracted by internal forces generated by the muscles of the body, which act on the levers of the skeleton. These internal forces are also multiplied, by internal moment arms that exist between the force vector of the muscle/tendon pulling on the bone and the point of rotation (joint).

Let’s add these internal moment arms, and repeat the exercise, focusing on elbow flexion for simplicity (Figure 2):

Bottom of the rep (Elbow flexion of 0º): Because the load hanging from the hands is directly beneath the elbow, there is no internal moment arm between the biceps insertion on the radius/ulna and the elbow, so the limited contractile force of the biceps is not multiplied. As noted above, there is no external moment arm between the load and the elbow, so the force of the load is not multiplied either.

First 1/4 of the rep (Elbow flexion of 45º): The external moment arm between the load in the hands and the elbow joint begins to increase, making the load feel heavier. At the same time, an internal moment arm is created between the biceps insertion on the radius/ulna and the elbow. The biceps muscle belly has shortened, increasing the potential for force production as it gets closer to resting length, and that biceps contractile force is multiplied by the internal moment arm to keep the load moving.

Halfway up (Elbow flexion of 90º): The external moment arm between the load and the elbow is now at a maximum, as is the magnitude of the force imposed by the load on the levers of the arm. At the same time, the internal moment arm between the biceps insertion on the radius/ulna and the elbow is also a maximum, with the biceps pulling at 90º on the radius/ulna. While the biceps have contracted even further, this multiplies what force you can generate from the biceps contraction, helping you to get through the sticking point.

Limit of Elbow Flexion (Elbow flexion of ~150º): The internal moment arm decreases, so you are pulling on the load less effectively (with almost fully shortened biceps). However, the external moment arm between the load in the hands and the elbow joint has decreased, so the force to be overcome is lessened.

One More Thing

When the weight gets heavy near the end of the set, you may throw in a little “English” into the movement to get through the sticking point. A layback can help to add momentum to the bar. In addition, the layback reduces the external moment arm between the load and the elbow, while maintaining the maximum internal moment arm between the biceps insertion and the elbow (Figure 3). This reduces the moment around the elbow joint, contributing to getting you through the sticking point.

The barbell curl is a simple exercise – single joint, movement in one plane only. An SSC should be able take the principles described above and apply them to complex movement patterns like a squat, deadlift, press and bench. The M.A.P. is not intended to be a checklist. You should be able to look at the model of a lift from any perspective, and start at any point. However, this framework may help you to grasp the interactions of mechanics, anatomy, and physiology and set the stage for deeper understanding

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