1. Comparison of Loaded and Unloaded Ramp Descent Jordan Thornley, B.Sc. and D. Gordon E. Robertson, Ph.D., FCSB School of Human Kinetics, University of Ottawa, Ottawa, Canada Methodology Participants: A sample population of five male volunteers participated in the study. Subjects walked down a ramp with a 10 degree decline. Five trials were completed carrying no load and five more trials were completed carrying 18.0 kg (40 lbs). Subjects were instructed to walk at a comfortable cadence. Procedure: A Kistler force plate collected the force data. A VHS camera recorded the sagittal view trajectories of markers placed on the left side of the body. The video data were digitized and then kinematics of the three segments of the lower extremity computed. After rotating the force data through 10 degrees they were combined with the kinematic data using inverse dynamics to obtain the net moments of force and their associated powers at the ankle, knee and hip (Winter & Robertson 1978). For comparative purposes the moments and powers were normalized to body mass and ensemble averaged over a stride cycle (foot-strike to foot-strike). Introduction Little research exists examining the kinetics and kinematics of sloped walking. Upon ramp descent, significant changes in hip, knee and ankle powers have been recorded at a grade of 19% (Kuster et al. 1995 ). However, no study has examined the compensatory effects of loaded ramp descent. It is believed that high loads placed on the lower extremity during downhill walking play a critical role in the development of joint and muscle soreness (Schwameder et al. 1999). Likewise, the implications loaded slope walking may play on degenerative joint disease and other lower limb pathologies is of value. This research will help evaluate the means by which we transverse uneven surfaces. Purpose To compare lower extremity work and power during loaded and unloaded ramp descent. 0 102030405060708090100 Percentage of Stride -4 -2 0 2 -4 -2 0 2 0 2 4 ITO Hip Knee Ankle Power (W/kg) K1 A1 K3 A2 Figure 7. Typical net moment powers for loaded ramp descent in a male subject. 0 102030405060708090100 Percentage of Stride -4 -2 0 2 -4 -2 0 2 0 2 4 ITO Hip Knee Ankle Power (W/kg) A1 A2 K3 K1 Figure 6. Typical net moment powers for unloaded ramp descent in a male subject. Figure 1. Digitized data and force vectors of loaded ramp descent of a male subject. There were differences between ramp descent and level walking as seen in Figures 6 and 7. For example, the peak negative power done by the plantar flexors (A1) was approximately eight times that of level walking. In contrast, the peak positive power done by the plantar flexors during push-off (A2) was about half that of level walking (Winter, 1991). Similarly, the negative peak powers by the knee extensors (K1) and flexors (K3) were approximately twice that of level walking. In contrast, the hip powers were slightly smaller than those reported for normal speed level walking (Winter, 1991). References Kuster M et al. (1995) Kinematic and kinetic comparison of downhill walking. Clin Biomech, 10, 79-84. Schwameder H et al. (1999) Knee joint forces during downhill walking with hiking poles. J Sport Sci, 17, 969-78. Winter DA (1991) Biomechanics and Motor Control of Human Gait. Waterloo: Waterloo Biomechanics. Winter DA & Robertson DGE. (1978) Biol Cybern, 29, 137-42. Summary The ankle was not required to generate additional propulsive force to carry a load down the ramp (see A2 of Figures 6 and 7). Likewise, the knee extensors were not required to absorb more energy during stance (see K1 and K3 of Figure 6 and 7). A lack of significant differences indicate that loaded ramp descent places no significant increases in the energetics of the ankle, knee and hip moments compared to unloaded ramp descent. These data suggest descending a ramp is a favorable method to carry loads across uneven surfaces. 0 20406080100 Percentage of Cycle -6 -3 0 0 3 0 3 6 Moment of Force (N.m/kg) ITO Hip Extensor Knee Flexor Plantiflexor Hip Flexor Knee Extensor Dorsiflexor Figure 4. Typical net moments for unloaded ramp descent in a male subject. Percentage of Cycle 0 20406080100 -6 -3 0 0 3 0 3 6 Moment of Force (N.m/kg) ITO Hip Extensor Knee Flexor Plantiflexor Hip Flexor Knee Extensor Dorsiflexor Figure 5. Typical net moments for loaded ramp descent in a male subject. Figure 2. Force signature during unloaded ramp descent in a male subject. Figure 3. Force signature during loaded ramp descent in a male subject. Unexpectedly, there were no significant differences between the peak net moments and powers at the ankle, knee and hip joints during loaded versus unloaded ramp descent (P>0.05). Figures 4 and 5 show the ensemble averages for a typical subject’s ankle, knee and hip moments during unloaded and loaded descent, respectively. Notice that during stance extensor moments predominated at all three joints. Figures 6 and 7 show the ensemble averages for the same subject’s ankle, knee and hip powers during unloaded and loaded descent, respectively. Although not significantly different (P=0.095) the negative work done by the knee extensors (K1 plus K3) was higher during loaded descent. Results and Discussion Loaded ground reaction forces (Figure 3) increased moderately relative to unloaded descent (Figure 2). Both force signatures had a bimodal pattern consistent with that of level walking. Biomechanics Laboratory Unloaded Loaded