ABSTRACT:
The
anterior cruciate ligament (ACL) is commonly injured in
athletics, requiring surgical intervention with serve injuries.
Although physical therapy protocols often utilize backward
treadmill walking following ACL reconstruction, there is little
research available which substantiates its use. Therefore the
purpose of this study was to describe the electromyographic
activity in the vastus medialis (VM), vastus lateralis (VL),
biceps femoris (BF) and semitendinosus (ST) during forward
walking (FW) and backward walking (BW) in ten normal subjects.
PURPOSE:
Following ACL
reconstruction, the knee joint often exhibits edema with
functional inhibition of the quadriceps muscles and weakness of
the lower extremity musculature. For the knee joint, closed
kinetic chain (CKC) exercises appear to offer the advantage of a
co-contraction of the quadriceps and hamstring muscles. The
co-contraction counteracts the anterior shear force on the ACL
that normally occurs with open kinetic chain exercises. In an
effort to restore normal quadriceps and hamstring activity,
therapists often use backward walking on a treadmill as a form of
CKC exercise. Although backward walking has been hypothesized to
increase quadriceps function and reduce ACL shear force through
hamstring co-contraction, little research is available to
substantiate these claims. Therefore the purpose of this study
was to study activity in the vastus medialis, vastus lateralis,
biceps femoris and semitendinosus muscles during forward and
backward treadmill walking with 3 different inclines.
METHODS:
Subjects.
Ten, normal, healthy subjects volunteered to participate in the
study. Instrumentation. To record the EMG activity,
surface electrodes were placed over the motor points of the VM,
VL, BF and ST muscles on the right side. To measure knee joint
motion, an electrogoniometer was applied across the knee joint.
Four foot switches were applied to the bottom of the foot over
the heel, first metatarsal, fifth metatarsal and great toe to
signal the position of the foot. Procedure. To normalize
the data, each subject was asked to perform a maximal voluntary
contraction (MVC) of each muscle studied. Each subject was then
asked to walk both forward and backward on a treadmill, at 3.0
mph and at 0, 10 and 15 degrees of incline while sEMG data was
collected. Data Analysis. The average peak activity of
each walking trial was calculated using the Myosoft and Norquest
software. Normalized values (% of MVC) were then calculated for
each trial. The knee ROM was also calculated for each trial. The
normalized values were then used to compare muscle activity in FW
and BW.
RESULTS:
Muscle
Activity. As compared to FW, BW increased the muscle activity
of the VM, VL, ST and BF regardless of the angle of incline (Fig.
1). The fifteen degree incline resulted in the highest level of
quadriceps and hamstring activity. The greatest percent increase
in muscle activity, from FW to BW, was observed in the vastus
medialis muscle (Fig. 2 and 3). Although the hamstring muscle
activity was increased in BW, the changes were not as marked as
for the quadriceps. ROM. BW required greater knee flexion
angles than did FW. The amount of knee flexion increased with
increasing angles of incline. Cadence. BW tended to
decrease both the duration of swing and stance phases compared to
FW. Increasing the degree of incline also decreased the swing and
stance durations.
Figure 1. EMG Activity in Forward and Backward Walking.
Figure 2. EMG Activity in the Vastus Medialis During Forward and Backward Walking at 0 Degrees of Treadmill Incline.
Figure 3. EMG Activity in the Vastus Medialis During Forward and Backward Walking at 15 Degrees of Treadmill Incline.
DISCUSSION:
The
results of this study parallel other research studies on FW and
BW. Other researchers have also found that BW requires increased
muscle activity and range of motion as compared to FW. BW
decreases stride length and increases cadence, both of which may
cause an increase in muscle activity. The increased cadence
increases the frequency of hamstring and quadriceps firing, thus
increasing overall activity. The increase in knee flexion ROM may
also increase the quadriceps activity during BW. During FW, the
quadriceps are relatively inactive during swing phase. However,
during BW the quadriceps are active in swing phase to control
foot placement prior to touch down. BW also requires concentric
quadriceps activity during stance phase to assist in knee
extension. During FW, the lower extremity motion relies on
momentum; whereas in BW there is less reliance on momentum and
therefore more muscle activity is required to move the lower
extremity.
CLINICAL IMPLICATIONS:
Because
of the increased muscle demands, especially in the vastus
medialis, BW should be cautiously implemented during
rehabilitation. Given the precautions, it appears that BW should
be implemented where increased knee range of motion and muscle
strength are the primary treatment goals.