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   Weight Training Exercises

For Fitness and Weight Control

Weight training has been shown to be one of the safest high intensity fitness excercises. In a 4 year study, Zemper (1990) examined the incidence of injuries caused through weight training in US college football teams. The study revealed that weight training possessed one of the lowest rates of injury among strenuous forms of exercise and sport.

Compressive vs Shear Forces
When training the legs and the lower back, lower back injuries are always a concern. At the International Conference of Biomechanics held in July 1995 in Finland , Dr Stuart McGill from the University of Waterloo in Canada , who is a world leader on lower back injuries, outlined some important information (McGill, 1995).

Firstly, the spine is much better at handling compressive forces as opposed to shear forces. Compressive forces occur when the spine is loaded in the purely vertical plane with the vertebrae pushed directly downwards. If standing upright with a barbell on your back in a squat position this is the force exerted on your spine.

Importantly, the back is well suited to handling this type of force and will tolerate a load in the order of 12,000 N (i.e. equivalent to a static load of 1,000 kg) before problems occur. However, the spine is not as well suited to shearing forces. These forces occur when the spine is pulled forward and can result in a slip disc.

If standing in an upright posture the compressive forces are those pushing the vertebrae together in the vertical plane, while shearing forces are those operating in the horizontal plane, tending to force some of the vertebrae forward. The back can only tolerate a shear force in the order of 2,000 N before problems will occur. Consequently, in any lifting exercise an effort should be made to maximize the compressive component of the load and minimize the shearing component.

Reducing Shearing Forces
For example, in a squat movement if the trunk is upright throughout the lift, the forces will be compressive. However, as one begins to flex the trunk forward the shearing component of the load increases dramatically. Hence in all lifting activities such as squats, deadlifts, cleans etc. one must make an effort to maintain an upright body posture throughout the lifts and keep forward flexion movements of the trunk to a minimum. If individuals are having difficulty in achieving an upright posture in a squat lift then the performance of the squat on a Smith machine, or the use of hack squats or front squats will allow for the adoption of a more upright body posture.

Placing Tension on the Muscles and off the Ligaments
When performing exercises involving lower back support, it is important to adopt a hollowed out back posture. This hollow back posture involves a slight degree of hyperextension of the back and really is the natural position of the back. Indeed you should be in such a posture now as you are reading this article.

To achieve it while lifting, one needs to throw the chest forward, the shoulders back, look upwards and push the buttocks out. Such a body posture should be adopted in all lower back supported lifts such as squats, deadlifts, cleans etc. This hollowed out back posture takes the stress off the ligaments of the lower back and places it on the muscles, reducing the likelihood of the occurrence of injury. Several lifts are technically difficult to perform and can be dangerous if performed incorrectly. Below is a description of the correct technique to be used for some of these exercises.

Squats
This exercise is performed while standing erect with a bar placed on the upper back. The bar should be located on the trapezius muscle and not on the cervical spine. If the lifter feels that the location of the bar is uncomfortable, a rubber mat or a towel should be placed between the bar and the back. The bar should be held against the body firmly by the hands. For safety reasons the squat exercise should be performed in a power rack which has bottom safety stops so that the bar can be rested upon these stops if the lift cannot be completed.

The feet should be positioned slightly further apart than shoulder width with the toes facing forward.

The movement commences from an upright posture and the individual lowers the body, mainly by flexing the hips and, to a lesser extent, the legs, until a knee angle of approximately 120 degrees is achieved. At this point the bar is raised by extending at the hip, knee and ankle joints to achieve an upright posture. It should be noted that the performance of heavily loaded deep full squats can stretch the cruciate ligaments of the knee joint making this joint unstable. Hence, a half squat movement is recommended.

Throughout the lift the shoulders are pulled back, the elbows rotated to a forward position, the head held up and the trunk, though angled slightly forward, should be relatively straight. In fact, the lower back should be curved slightly inwards i.e. hollowed out.

Squats are very popular among athletes; however they are often performed incorrectly. The most common problem involves leaning too far forward during the exercise, which greatly increases the stress placed on the lower back. Lifters must keep the trunk very rigid and basically upright throughout the lift. It is vitally important that the upper back remain rigid and lifters should be encouraged to look upwards, keep the shoulders back and rotate the elbows into a forward position.

The technique in the squat can be readily assessed by watching the individual from the side. The weight should be located almost directly above the hips and ankles throughout the lift. If lifters have a tendency to fall forward during the lift then the exercise should be performed on a Smith machine so that the bar remains in a vertical plane.

Squats can sometimes be difficult for many athletes in lower body dominated sports as their lower bodies are developed to a far greater extent than their upper bodies and thus the limitation to perform the squat is generally the ability of the upper body to stabilize the load on the back. This problem can also be reduced by using a Smith machine or by per forming the hack squat exercise. The squat exercise strengthens the quadriceps, hamstrings and gluteal muscle groups as well as the erector spinae muscles.

Deadlifts
The lift commences with the athlete crouched over the bar, with the feet spaced slightly closer than shoulder width and the bar positioned very close to the individual. The bar is gripped with one palm facing downwards and the other facing upwards and the hands spaced approximately shoulder width apart. This type of grip greatly increases the load that can be held.

It is important that prior to the commencement of the lift, the athlete is dominantly flexed about the knee and that the trunk is slightly flexed forward, but relatively straight. In fact, the lower back should be slightly curved inwards i.e. hollowed out, so that the shoulders are pulled back, the head looking up and the buttocks pushed out.

The bar is lifted explosively to waist height in one co-ordinated movement of the legs, thighs and trunk. The arms should be straight through out the lift and not contribute to the upward movement of the bar. The arm musculature is simply too weak to lift the loads encountered during deadlifts, and their attempted contribution can result in tears to the biceps brachii and brachialis muscles.

Throughout the lift the bar should be kept close to the body. In fact, the bar should be in contact with the lower limbs throughout the entire movement and should be lifted upwards and backwards as the individual leans back at the completion of the lift. Baby powder can be applied to the lifter's legs in order to reduce the friction of the bar.

Heavy deadlifts are a test of grip strength as much as thigh and trunk strength and in order to enhance the effectiveness of the grip it is often necessary for the athlete to apply chalk resin (magnesium carbonate) to the hands.

The bar should be lowered to the floor in a reasonably controlled manner. Again during the eccentric phase the movement occurs mainly due to the flexion of the legs and thighs. The trunk will be slightly flexed but must remain straight.

The lift is performed with a belt which serves to increase the support given to the lower back and abdominal region. If performed incorrectly, this exercise can cause injury to the vertebral column, particularly when heavy loads are used. Common mistakes include insufficient use of the legs and consequently, excessive flexion of the trunk. Thus the movement almost becomes a stiff-legged deadlift. Further, the bar is sometimes lifted with the shoulders in a forward position with the head down which results in a humped appearance in the upper back, increasing the likelihood of injury in this region.

This exercise should be avoided if the athlete has a history of lower back problems.

This exercise strengthens the erector spinae, quadriceps, hamstring, gluteal, upper back and forearm musculature.

Lower Back Injuries
It is important to realize that in most cases lower back injuries are not caused by one single traumatic event. More typically they are the result of a large number of smaller stresses that often occur over many years (McGill, 1995). Thus, many people may incorrectly perform the above exercises for years with no adverse effects. However, if they continue exposing their lower back to undue stress they will be significantly increasing their likelihood of experiencing the discomfort of lower back injury in the future.

A further point to be aware of is that you do not have to lift heavy weights to stress your lower back. In certain positions the relatively long lever length of the trunk can result in such a poor mechanical position that even relatively light weights can place undue stress on the lower back. Thus, adherence to correct technique on all exercises involving the lower back is essential, independent of load.

Conclusions
Weight training is one of the safest high intensity recreational pursuits. Nevertheless the performance of exercises with correct form is essential, particularly those involving the lower back. The lower back is better suited to compressive rather than shear forces and hence an upright posture should be adopted throughout.

Source: http://www.afpafitness.com

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