Common Resistance Training Mistakes

Force Vector and Alignment Errors
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Dumbbell Shoulder External Rotation



Force must be through the transverse plane
lying on side
cable
Surgical or exercise tubing
Bottom line: with a dumbbell, perform this exercise lying on your side

Dumbbell Triceps Kickback (elbow too low)
Triceps Kickback (correct form) already has half the effective range of motion as other triceps exercises
greatest resistance occurs at full extension when weight travels parellel to gravity
See Gravity Vector and diagram
Peak contraction
If elbow is too low (see animation)


very little effective range of motion
exerciser typically tries to compensate and flexes arm against graivity
performing something that resembles an hammer curl
even that motion comprimises range of motion.
resistance does not travel parellel to gravity at end of motion
less weight is needed
possible causes
weight could be too great
exerciser is not bent over enough
body and arm need to be positioned horizontal
exerciser merely tries to bend over slightly (typically without arm support) thinking that will do.

Shoulder Shrugs (shoulder rolls)



In an upright posture, the upper traps and middle traps resist weights against gravity (downward force) as they elevate the scapula
see correct form
Although it is true the middle and lower trapezious can also retract the scapula on a continuum of planes
they resist such a load retracting against a resistance on a transverse plane during general back exercises
or by upward rotation on a frontal plane during shoulder exercises
Bottom line: It's only neccessary to raise and lower the shoulders during shrugs. The lower and middle trapezeous will be exercised during other basic exercises

Cable Quad / Glute exercises (cable perpendicular to line of push)
Added resistance on weight stack will not effect difficulty of exercise
no or little movement of weight stack during exercise
Correct form:
pull of cable needs to travel:
reletively vertical under exerciser
eg: Cable Squat
approximately parellel with line of push
eg: Cable Lunge

Rear Lateral Raise (shoulder extension or external rotation)


When elbows travel under shoulders
Latissimus Dorsi takes the majority of the load
Shoulder extension
Rear delts are still exercised
Forfeits the purpose of even performing an auxiliary isolated movement
Isolation
Lats can be exercised more efficiently with rows and pulldowns
Shoulder external rotation
Rear delts do assist in external rotation
but performing the exercise correctly will work target muscle more effectively
Additional flaws
Weight is typically thrown up
Weight travels parellel to gravity at end of contraction
See Gravity Vector and diagram
Peak contraction
Lighter weight should be used so it can be lifted without excessive momentum
Elbows bent too much

Shorter lever arm means less force (See Lever Arm Length)
Use less weight so arm is only slightly bent
Low back is rounded
Although knees are bent to allow greater flexion through hips, the back should be straight
May be corrected with coaching if hamstrings are adequately flexible
Correct form
Elbows directly lateral to shoulder at top position
Upper arms travel perpendicular to body
Practically no Latissimus Dorsi involvement
Weight should be lifted with control
Elbows should not be bent too much
Low back straight

Low Back Alignment Exceptions
Guidelines recommended for particular exercises may not apply to certain exercises
Example
Dumbbell Bent-over row
practically no torque on low back since torso is supported by arm
bend in spine may be overlooked since it presents no risk
Straight Leg Deadlift and Cable Row with articulating spine
exercises that intentionally exercise the spinal erectors through a full range of motion (spinal extension in a controlled systematic manor)
See Dangerous Exercise Essay
Individuals with certain injuries or predisposition to injury may need to take additional precautions.


Source: exrx.net