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Lifting a Lightweight Object
Introduction:
The task of lifting objects is a common physical demand in both the
home and the workplace. The action of lifting can include picking up a
dropped pencil at the office, taking out the trash, heaving large boxes while
moving, etc. Proper lifting techniques stress concepts such as vertical
gravity line, base of support, short lever arms, and lordosis. Despite this
knowledge, lifting accidents and injuries do occur. Over 60% of all lifting
injuries in the workplace result from overexertion, nearly one third are due
to accidents in which improper footing or improper weight expectation
occurred. Still other injuries are cumulative, in which minor subclinical
injuries accumulate damage over time.
Most lifting styles focus on minimizing stressors on the lower back; in
fact, 400,000 new cases of work-related injuries occur to the lower back
each year. However, no style of lifting can minimize the stressors at the
hip, patellofemoral joint, and the ankle joints. Research shows that strong,
flexible hamstrings and quadriceps can help protect the back while lifting.
Maximum joint angles suggested for safe lifting are 125 degrees at the hip,
140 degrees at the knee, and 25 degrees at the ankle.
The purpose of our presentation is to analyze one lifting situation
involving a lightweight object, in this case, a single branch in the woods. We
will focus on the lower extremities—the hip, the knee, and the ankle.
However, it is important to mention the general status of the upper body
and extremities since they are certainly involved.
Pre-lifting Phase : Trunk and Upper Body Motions
In our scenario, the subject is jogging through the woods when she
encounters a branch in the way and abruptly stops. At this point, the
shoulder girdle goes into protraction with the intent to eventually remove
the branch. The shoulder joint goes into slight flexion as does the elbow
joint, and the forearm goes into pronation as it readies to pick up the object.
The hand prepares to lift by using a spherical grip around the rounded shaft
of the branch. The trunk does not rotate nor bend; it remains stabilized by
the deep transverse muscles which are in a low level of contraction. There is
slight lordosis of the spine as the subject keeps her back from arching
forward.
Phase I: Starting the Lift
The Hip (Figure 1.1) In the starting position, the action of the pelvic
girdle is a slight anterior tilt, with an increased lumbar lordosis. The motion
at the hip joint is hip flexion. The muscles working are the gluteus maximus,
semitendinosus, semimembranosus, and the long head of the biceps femoris.
These muscles are producing an eccentric contraction. The antagonists are
the hip flexors which are rectus femoris, iliopsoas, and pectineus. Because
the distal segment is stabilized, this motion is closed chain.
The Knee (Figure 1.2)
The starting action is knee flexion. The muscles
include the rectus femoris, vastus lateralis, vastus intermedialis, and vastus
medialis, which are known as the quadriceps group. They are going into an
eccentric contraction as they stretch over the patella, preventing gravity
from causing the knee to “buckle.” Although one would think that the
hamstrings (biceps femoris, semimembranosus, and semitendinosus are
involved in knee flexion, they are, in fact, the antagonists in this situation.
The popliteus, which initiates knee flexion, is contracting at this phase as
well, although it is an assist to knee flexion at best. At the patellofemoral
joint, the convex femur is rolling posteriorly, sliding anteriorly, and spinning
laterally on the concave tibia. This is because the motion is distal segment
stable (closed chain).
The Ankle (Figure 1.3) The action of bringing the body down toward the
ground causes an eccentric contraction of the soleus, which is the prime
mover. The gastrocnemius, normally the much stronger muscle, is put on
slack at the knee joint and therefore is an assist at best. Additionally, the
plantaris is a weak assist along with the soleus in eccentrically contracting to
stabilize the ankle. While the ankle is placed in dorsiflexion, the tibialis
anterior is not contracted and acts as the antagonist in this situation. The
action is closed chained—the distal segment is stationary. The talocrural
joint, which is a hinge joint, is allowing dorsiflexion. The toes of the right
foot remain in extension; the toes of the left foot are hyperextending on
the way down. This is due to an eccentric contraction of the flexor
digitorum longus and the flexor hallucis; again, one would think that the
extensors are doing the work, but they are the antagonists. The action of
the phalanges is also close- chained.
Phase II: Retrieving the Object
The Hip (Figure 2.1) The gluteus maximus, semitendinosus,
semimembranosus, and biceps femoris (long head) are continuing to contract
isometrically, because no movement is occurring. Muscles that are stabilizers
include the gluteus medius and gluteus minimus as well as the sartorius. The
tensor fascia latae is included as a stabilizer, also. The hip flexors (rectus
femoris, iliopsoas, and pectineus) are still the antagonists. The pelvic girdle
has a more pronounced anterior pelvic tilt.
The Knee (Figure 2.2) When retrieving the object, the knee continues to
be in flexion with the primary movers being the rectus femoris, the vastus
lateralis, vastus intermedialis, and the vastus medialis. The contraction in
this position is isometric since there is no movement, but instead, a “holding
down” situation. The hamstrings group, including the biceps femoris,
semimembranosus, and semitendinosus are the antagonists.
The Ankle (Figure 2.3) As the body remains down and the ankle is in
dorsiflexion, the soleus continues to contract in an isometric fashion,
keeping the balance and strength steady. The toes are in extension; the
flexor hallucis longus and the flexor digitorum longus are also on an
isometric contraction as they hold the foot in place. Note that in the left
foot, the toes are in hyperextension isometrically.
Phase Three: Returning to Starting Position
The Hip (Figure 3.1) The hip is now in going into extension, and the hip
extensors are still doing the work of contracting. They include the gluteus
maximus, semitendinosus, semimembranosus, and biceps femoris (long head).
They are concentrically contracting as the body moves against gravity. The
antagonist continue to be the hip flexors, which are the rectus femoris,
iliopsoas, and pectineus. The pelvic girdle is returning to neutral position.
The Knee (Figure 3.2) The knee is going into extension as the object is
lifted. The rectus femoris, vastus lateralis, vastus intermedialis, and vastus
medialis are contracting concentrically. At the patellofemoral joint, the
femur has an anterior roll as it slides posteriorly. Additionally, there is a
medial spin of the femur with the last twenty degrees of extension.
The Ankle (Figure 3.3) In returning to the starting position, the soleus is
now concentrically contracting as the muscle belly shortens. There is less
stretch at the calcaneus now since the lower leg is raising. The flexors are
also concentrically contracting as the lower leg raises.
Conclusions:
Although many lifting techniques and work-related training programs
focus on preventing injury to the trunk, particularly to the back and spine,
our focus was to discover the role of the lower extremities in lifting. As
seen, there is much muscle action occurring at these three joints, with
potential injury at any one of them. We believe that instruction in lower
extremity motions, in addition to trunk, would be helpful to include in overall
lifting techniques. Smooth, safe movements of the hip, knee, and ankle can
help prevent upper body injuries. There are many ways to approach the
action of lifting. The example we used is one way of lifting; other more
effective ways could have been utilized. However, lifting is often an
unplanned, immediate reaction to something dropped or in the way; we don’t
always consciously think about our body motions.
Works Cited
Jacobs, K., Bettencourt, C: Ergonomics for Therapists. ButterworthHeinemann, 1995, pp. 97-112.
Pierson, F., Fairchild, S: Principles and Techniques of Patient Care. Elsevier
(USA), 2002 pp., 70-73.
Lippert, L.: Clinical Kinesiology and Anatomy. F.A. Davis Co., pp. 231-283.