It is important to have at least a basic understand the mechanics of an exercise you intend to perform or teach, whether it's a weight training or flexibility exercise. Exercises require particular positioning of the body in order for target muscle groups(s) to be exercised optimally. So you may better understand this concept, let's begin with a ridiculous example of someone attempting to perform a Barbell Bench Press, but standing upright instead of lying supine. The pectoralis muscles, after all, are suited for drawing the arms forward and inward across the chest (transverse adduction). The movement is correct. So why would not this exercise work? The other crucial requirement obviously involves the alignment of target muscles against the resistive force. In the case of free weights that force is gravity pulling downward. This means if we are to exercises the desired muscle groups in this movement, we must orientate our body supine on a bench so our muscles contract under the force of gravity acting upon the weight. However with machines we can alter the direction of force. Gravity still acts on the weight but the machine alters direction of force via use of lever(s) or cable pulley(s). This means on lever chest press machine, for example, we would need to be upright with the hands behind the lever handles to work these same muscles. In any case, the alignment of target muscles must be positioned against the resistive forces, which ever direction they happen to be orientated. If we want to target the upper chest (clavicular head) on some sort of barbell press, we would need to know the action of this muscle and position our body and its appendages accordingly. In this case we would lie on an incline bench, instead of a flat bench. We would however still need to push the weight upward against gravity as we do in the Barbell Incline Bench Press. Notice the similarities and differences when we perform the Cable Standing Incline Chest Press targeting the same muscle group but using a specific positioning on an adjustable dual cable apparatus to alter the direction of force. Other subtle variations to the body's alignment or it's appendages can make the difference between targeting the muscles or working an entirely different set of muscles. In other cases with less than ideal alignment, the target muscle may still be exercised somewhat, but likely not as nearly as effectively as a more ideal positioning would allow. Here are some common alignment errors involving some obvious and not so obvious examples: Dumbbell Shoulder External Rotation Errors (upright posture) Target muscle moves body segment through plane perpendicular to resistance Force must be through the transverse plane lying on side cable surgical or exercise tubing Correct form Dumbbell (lying) Cable (standing) Bottom line: with a dumbbell, perform this exercise lying on your side Dumbbell Triceps Kickback Errors (elbow too low) Effective range of motion decreased by drop in elbow 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 parallel to gravity See Gravity Vector and diagram Peak contraction If elbow is too low (see animation to right) very little effective range of motion exerciser typically tries to compensate and flexes arm against gravity performing something that resembles a hammer curl even that motion compromises range of motion. resistance does not travel parallel to gravity at end of motion less weight is needed possible causes weight could be too great exerciser is not bent over enough upper arm need to be positioned horizontal exerciser merely tries to bend over slightly (typically without arm support) thinking that will do. Shoulder Shrugs Errors (shoulder rolls) Rolling (horizontal movement) is nonsensical Weight moves perpendicular to gravity 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 trapezius 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 necessary to raise and lower the shoulders during shrugs. The lower and middle trapezius will be exercised during other basic exercises Also see ROM Criteria Cable Exercise Errors (cable perpendicular to line of force) Added resistance through cable (weight stack via pulley) is aligned perpendicular to target muscles does not effect difficulty of exercise no or little movement of weight stack during key motion of exercise Correct form: pull of cable needs to travel: relatively vertical under exerciser e.g.: Cable Squat approximately parallel with line of push e.g.: Cable Lunge Some so called exercise experts evidently even fail to understand this important biomechanical concept For example, Hammer Strength Training Vest exercise video demonstrates numerous movements that load exercises perpendicular to line of force of synergist muscles. Compound Wide Grip Upper Body Exercise Errors (too wide of grip) Recommended grip width for wide grip exercises elbow width, when elbow is same height/plane as shoulders subtle deviations may still be used (i.e. 2 cm narrower or wider) Wider grip decreases range of motion through shoulder when elbow is extended through elbow when shoulder is in transverse extension or adduction decreases relative involvement of assisting muscles turns basic exercise into auxiliary exercise may as well implement auxiliary exercise through fuller range of motion Example wide grip exercises Bench Press Incline Bench Press Pulldown Chin-up | Pull-up Shoulder Press Also see Dip Bar Width Above line drawings from Trainer ClipArt.

Lateral Raise Errors (shoulder external rotation) Shoulder external rotation If dynamic shoulder external rotation occurs during lift Infraspinatus and Teres Minor become primary mover Shoulder external rotation can be confused with shoulder abduction little shoulder abduction is actually occurring despite weight being raised If static shoulder external rotation is maintained throughout movement Shoulder is not kept externally rotated. ie: elbows drops below wrist Anterior Deltoid becomes primary mover In either case, Lateral Deltoid involvement is dramatically decreased. Purpose of movement is defeated Other more effective exercises may as well be used to exercise these muscles that are unintended exercised. Shoulder Extension Elbows travel behind shoulders lessened emphasis of lateral deltoid Correct form: At top of movement, elbows (not necessarily dumbbells) should be directly lateral to shoulders since elbows are slightly bent forward. Throwing weight up Decreases deltoid involvement particularly if momentum originates from sudden extension of hip or spine. Complete upright position Line of pull can be shifted to anterior deltoid unless extreme internal shoulder rotation is executed See correct form Rear Lateral Raise Errors (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 pull-downs Trainees typically require feedback by mirror if not by a trained coach to determine if their arms are following the correct path 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 parallel 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 See Barbell Bent-over Row Comments 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 Lower back straight Low Back Alignment Exceptions Proper lifting guidelines regarding splinting the spine (keeping back straight) or lifting with the legs may not necessarily 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 Dumbbell Seated Rear Lateral Raise little torque on low back since thighs provide support for torso bend in spine may be overlooked since it provides little risk Straight Leg Deadlift and Cable Row with articulating spine exercises that intentionally exercise the spine and spinal erectors through a full range of motion Spinal extension in a controlled systematic manor Adaptation criteria are properly applied See Dangerous Exercise Essay and Low Back Debate Individuals with certain injuries or predisposition to injury may need to take additional precautions.