Knee joint forces in uphill, downhill and level walking

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Knee joint forces in uphill, downhill and level walking at different gradients
H. Schwameder, R. Roithner, R. Burgstaller, E. Müller
Institute of Sport Science, University of Salzburg, Austria
Introduction
Lower extremity joint loads in walking change substantially with the gradient as it has been reported in
several studies (Schwameder et al. 2000, Davis et al. 1995, Kuster et al. 1995). The most distinct
differences concerning net joint forces and moments have been found for the knee joint (Kuster et al. 1995,
Schwameder et al. 2000). The actual knee joint forces concerning this particular issue, however, have not
been reported in the literature so far. Thus the purpose of this study is to determine structure forces within
the knee joint in level, uphill and downhill walking as a function of the gradient. The results may contribute
to find the biopositive window of knee joint loading in walking and hiking as a basic preventive concept
and to develop rehabilitation training programs.
Methods
22 healthy students (28 yrs, 1.76 m, 72.5 kg) were asked to walk on a ramp with an integrated force plate
(AMTI, 500 Hz) at different gradients. Both, the ramp and the force plate were adjustable to declinations
and inclinations from –24° to +24° in steps of 6°. 2D kinematic data (sagittal plane, 50 Hz) were collected
using a video camera located perpendicular to the ramp. During data analysis the local coordinate systems
were aligned and the data sets synchronized. A planar knee model was used to calculate knee joint forces
based on the collected kinematic and kinetic data (Schwameder et al. 1999). All knee joint forces calculated
(tibiofemoral compression [Fct] and shear forces [Fst], patellofemoral compression forces [Fcp], patellar
tendon forces [Fp] and quadriceps tendon forces [Fq]) were normalized to body weight (BW) and
time-normalized to support phase from heel-strike to toe-off.
Results
Table 1 shows the averaged peak values of the flexion moments and selected knee joint forces as a function
of the gradient. All knee joint forces, except the tibiofemoral shear forces, were lowest for level walking
and increased continuously with the gradient both, in uphill and downhill walking. Downhill walking
caused higher peak knee joint forces than uphill walking at the same gradient. In downhill walking at 24°
knee joint forces can be up to six times higher compared to level walking. Interesting is the result that the
tibiofemoral shear forces decrease in uphill walking with the inclination of the slope.
Two examples of the time history of knee joint forces (tibiofemoral shear forces and patellofemoral
compression forces) for level as well as for uphill and downhill walking at 24° are presented in Fig. 1.
Gradient
[deg]
Flex. moment
[BW]
Fct
[BW]
Fst
[BW]
Fcp
[BW]
Fp
[BW]
Fq
[BW]
-24 2.47 7.2 1.4 7.1 5.9 7.5
-18 2.17 6.3 1.3 5.9 5.1 6.3
-12 1.95 5.8 1.2 4.4 4.6 5.2
-6 1.28 4.0 0.9 2.3 2.3 3.0
0 0.75 2.7 0.6 1.3 1.7 1.8
6 0.97 3.3 0.7 2.0 2.3 2.5
12 1.25 4.0 0.7 3.2 3.0 3.6
18 1.28 4.3 0.4 4.4 3.2 4.6
24 1.41 4.6 0.3 5.7 3.5 5.7
Table 1: Knee flexion moments and knee joint forces during downhill, level and uphill walking at diffent gradients

Figure 1: Tibiofemural shear forces and patellofemoral compression forces in downhill, level and uphill walking
Both, in level and downhill walking high tibiofemoral shear forces indicating loads on the ACL can be
observed in the first part of stance phase. Compared to level walking the peak forces in downhill walking
are up to three times higher. In uphill walking the shear forces are small during the entire stance phase.
In level walking the patellofemural compression forces show a typical wave with local maxima at 25% and
85% of stance phase. During the entire stance phase the forces are relatively small. In uphill walking the
Fcp-forces increase substantially in the first part of stance phase compared to level walking while in the
second half of stance phase the shape of the curves are more or less the same. The highest patellofemoral
compression forces can be observed for downhill walking. The shape of the curve is similar to the one for
level walking. The amount of the forces, however, are about six times higher during the entire stance phase.
Discussion
The results of this study show that the knee joint forces (peak values and time courses) in walking change
substantially with the inclination of the slope. The knee joint forces differ both, concerning peak values and
time courses, from knee flexion moments and illustrate clearly the necessity of joint models to study loads
on joint structures. Many hikers suffer from knee pain and injuries after long and excessive descents. The
results of this study intensify the assumption that high loadings on knee joint structures cause pain and long
term injuries observed in hikers.
The results contribute to training recommendations in walking and hiking to optimally stimulate knee joint
structures without overloading. Patients after ACL reconstruction, for example, are recommended to
stimulate muscle activity by level and uphill walking. By this most of the structures are highly loaded but
there is only little stress on the ACL as the shear forces are small. On the other hand downhill walking
should be avoided completely due to the high stress on the ACL in this situation.
Retropatellar knee pain is common in hikers during or after long descents. This fact can be explained by the
high patellofemoral compression forces during the entire stance phase. It is worth to think about measures
to reduce these high loadings by adaptation of the downhill walking speed and technique or by using hiking
poles (Schwameder et al. 1999).
References
Davis M et al. 1995. Clin Orthop 310, 211-217.
Kuster M et al. 1995. Clin Biom 10, 79-84.
Schwameder H et al. 1999. J Sports Sciences 17, 969-978.
Schwameder H et al. 2000. Proceedings 18. Intern. Symposium on Biom. in Sports, Hong Kong, 983.
Tibiofemoral shear forces
-0.5
0
0.5
1
1.5
0 25 50 75 100
% stance phase
*BW
-24°
0°
+24°
Patellofemoral compression forces
-2
0
2
4
6
8
0 25 50 75 100
% stance phase
*BW
-24°
0°
+24°