Parallel Bar Dips
The diagram shows the exercise pretty much how most (mainly men) would perform bar dips. The anatomical parts most vulnerable in this exercise are the anterior (front) shoulder structures. To specifically name them, the long head of biceps tendon, the supraspinatus tendon and the subacromial bursa.
The reason why these structures are vulnerable is that at the bottom of the movement, the shoulder blade tips into what we call an ‘anterior tilt’ position. This happens due to a lack of shoulder extension at the bottom of the movement (the elbows behind the body position). The lack of shoulder extension is a result of tight pec minor and tight pec major (particularly the clavicular head). This creates a situation whereby the bony arch of the shoulder (the acromian process) gets in the way of the above mentioned structures. As a result the soft tissue structures (particularly the biceps tendon) can be compressed and damaged at the bottom of the movement.
I have seen 2 very serious full rotator cuff tendon tears in the gym going male population in 13 years. Both patients had been performing heavy weighted parallel bar dips at the time.
End result was a full surgical rotator cuff repair and 6 months out of the gym.
45 degree leg press
The dangerous part of this movement is at the bottom – when the knees approach the chest. As the hip flexes (as the thigh approaches the trunk), at a point around 90 degrees (this will depend on flexibility), the pelvis will move into what we call posterior pelvic tilt and the lumbar spine starts to flatten out and then curve into flexion (rounded lower back). The structure most at risk with this posterior pelvic tilt is the lumbar spine disc. Research shows that the amount of disc pressure created when the lumbar spine is flexed is considerable. Enough to either bulge a disc or prolapse a disc.
The amount of posterior tilt will depend on the flexibility in the hips, particularly in the gluteal muscles and the adductor magnus muscle.
A way to find out your safe hip flexion range is to place your hand under the arch in your lower spine at the top of the movement (when the legs are straight). Then as you lower into hip flexion, feel for when the spine starts to flatten in your hand. Allow 10 degrees more hip flexion and this is reasonably safe. Anymore than 10 degrees past this point then the lumbar spine becomes a risk.
This is probably the most useless gym exercise ever invented. The reason being that when performed incorrectly (and almost all variations are performed incorrectly) the movement defies the basic biomechanics of the shoulder joint. When the arm abducts (lifts away from the body) the ball of the upper arm bone (humerus) should rotate externally. Compare this yourself if you raise a straight arm out to the side and above your head with your thumbs pointing upwards and then thumb pointing downwards. Feel the difference? With the thumb up, the humerus is able to externally rotate and allows you to get more range.
This external rotation is important because if you don’t, there is a knob of bone on the side of the ball of the humerus (called the greater tuberosity) that will hit (or impinge) on the bony arch of the shoulder called the acromian process. If this happens, then the soft tissue structures such as the subacromial bursa and suprapinatus tendon will get squashed. And here is the problem with the upright row, the further the hands are apart then the greater the chance of not being able to externally rotate the humerus. Stick with lateral raises, they are much safer.