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To analyse an exercise, look at the following:
- Work out which is the concentric (work/effort) phase and which is the eccentric (returning) phase
- Joints involved in the exercise
- The movements that occur at the joint(s) during the concentric phase
- The muscles that cause these joint actions (the prime mover/agonist)
(1) The first thing you need to do is to determine which phase (i.e. either up or down) is the concentric phase. The concentric phase is the ‘work’ or ‘effort’ phase. With fixed resistance machines in the gym this is easy to work out, as the concentric phase is always when the weight stack goes up.
With free weight exercises (using dumbbells, barbells, bodybars, etc) and body resistance exercises (e.g. press up and squat), this becomes a bit trickier. As a general rule, when you are lifting a weight (such as a dumbbell or body weight) against gravity, you are in the concentric phase; likewise, when you are lowering in the same direction as gravity, then you are working eccentrically. The muscle(s) shorten during the concentric phase to lift against gravity, and the same muscle(s) lengthen to lower with gravity when working eccentrically (acting as a brake to prevent you injuring a muscle/joint or collapsing in a heap!).
When we apply this to the press up, the concentric phase occurs when you are pushing yourself up from the floor against gravity; and the eccentric phase occurs when you lower yourself down to the floor with gravity (concentric=up; eccentric=down). The same muscles are working in both phases (they shorten during concentric, and lengthen during eccentric).
The same applies to the squat – the concentric phase occurs when you raise yourself from the squat position (i.e. stand up) because you are pushing your body weight upwards against gravity; and working eccentrically when you lower yourself into the squat position (with gravity). The same muscles are working for both phases – they shorten on the way up (concentric) and lengthen on the way down (eccentric).
With the bicep curl, the concentric (work) phase occurs when the dumbbell is raised towards the shoulders, and the eccentric phase is when the dumbbell is lowered back down.
(2) Now we have determined the concentric/eccentric phases, we need to identify the main joint(s) involved during the movement. In the case of the press up, the joints we need to note are the shoulder and elbow joints. For the squat, they are the hip and knee joints that move, and for the biceps curl it is the elbow.
(3) Next, we identify the joint actions for the concentric phase. For the press up, the concentric (up) phase occurs when you push yourself up off the floor. Depending on how you position your hands, either flexion or horizontal flexion occurs at the shoulder. There will also be elbow extension. For the squat, the concentric (up) phase occurs when you stand up straight. Knee extension and hip extension therefore occur. For the biceps curl, the concentric (up) phase occurs when the dumbbell is lifted towards the shoulder. Therefore, elbow flexion takes place.
(4) Now we know the joint action(s), we can determine the agonist/prime movers (i.e. the muscles that do the work during the exercise). To do this, you need to look at the muscles that cause the joint actions during the concentric phase (the work or effort phase), as it is they that have to contract (and do the work) to lift the resistance or your body weight up against gravity. For the press up, the muscle that causes elbow extension is the triceps and the muscle that causes horizontal flexion (or flexion) is the pectoralis major (i.e. these are the prime movers/agonists causing the joint actions during the concentric phase). For the squat, the muscle that causes knee extension is the quadriceps, and the muscles that cause hip extension are the gluteus maximus and the hamstrings. For the biceps curl, the muscle that causes elbow flexion is the biceps. Please note that these same muscles are worked for both the concentric and eccentric phases – they get shorter during the concentric phase and longer during the eccentric phase.
Now we know the prime movers/agonist, we can determine the antagonist muscles (put simply, the muscle usually found on the other side of the body that has to relax to allow the prime mover to work). For the press up, the antagonist of the triceps is the biceps, and the antagonist of the pectorals is the trapezius and latissimus dorsi. For the biceps curl, the antagonist of the biceps is the triceps.
The above steps can be done with any exercise:
- Abdominal curl – the concentric phase is when you lift the shoulders off the floor against gravity. The joint moving is the spine, the movement is flexion. The rectus abdominis causes spine flexion, hence that is the prime mover. The antagonist is found on the other side of the body and is the erector spinae. The eccentric phase occurs when you lower the shoulders back down to the floor (you are still working the abs however).
- Calf raise – the concentric phase is when you lift the heels off the floor, lifting the body up against gravity. The joint used is the ankle; the joint action is plantar flexion; the muscles causing plantar flexion are the gastrocnemius and soleus. Hence, the prime movers are the gastrocnemius and soleus. The eccentric phase is when you lower the heels back down to the floor and these two muscles are still used (but get longer). The antagonist is found on the other side of the lower leg – the tibialis anterior.