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.
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