BIOMECHANICS OF ASCENDING AN INCLINE

Jon Singer and D. Gordon E. Robertson

School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada E-mail: jon_singer@hotmail.com and dger@uottawa.ca

INTRODUCTION This project was initiated to compare the work and power requirements of the net moments of the lower extremity during ramp ascent with those to level walking. Ramps are a common means of ambulation and the transportation of materials (Robertson & Ellwood, 1995) from one level surface to another. Yet little research has ever been done on ramp ascent. To permit an assessment of this activity comparison with established normative data from level walking is possible based on the data presented by Winter (1991). One useful tool for comparing walking on a level surface to walking up an incline is the support moment. Winter (1991) outlined this concept, that during the stance phase of walking people produce a characteristic bimodal impulse that is the sum of the three extensor moments of the lower extremity. The support moment (Msupport) was defined as,

Msupport = -Mhip + Mknee - Mankle where the negative signs reverse the polarities of the hip and ankle moments so that extensor moments at each joint are positive while flexor moments are negative. METHODS Eight subjects were recruited to walk across a laboratory walkway and ascend a 10-degree ramp. After informed consent, the subjects were filmed walking at their self-selected pace up the incline. They stepped so that one foot landed on a level force platform, the other foot landed on the bottom of the incline and the first foot

stepped onto a second force platform imbedded in the ramp. Video data were reduced using the APAS system and then processed with the Biomech Motion Analysis System (www.health- .uottawa.ca/biomech/software). The video data were filtered and then kinematics of the three segments of the lower extremity computed. The force platform data were rotated to compensate for the 10-degree incline and then combined using inverse dynamics with the kinematic data to obtain the net moments of force and their associated powers at the ankle, knee and hip (Winter & Robertson, 1978). Lastly, the three moments were added to obtain the support moment. For comparative purposes the moments were normalized to body mass. RESULTS AND DISCUSSION Figure 1 shows a typical subject’s support, hip, knee and ankle moments during the step immediately before the ramp and the same foot’s moments while on the ramp (second step on ramp). Notice that the first (ground level) support moment was approximately the same as normal level walking but the support moment on the ramp was slightly lower. All subjects showed this slight decrease in the amplitude of the support moment as well as having a smaller second peak for both steps (step before the ramp and on the ramp). The smaller second peak may be due to the reduced need to swing and decelerate the lower extremity before landing. The ramp’s incline reduces the need to decelerate the foot prior to foot-strike and provides a horizontal stopping force.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Time (seconds)

-2

-1

0

1

-1

0

1

-1

0

1

-1

0

1

2

3 N

et m

om

ents

of

forc

e (N

.m/k

g)

Trial: RUAP03

FS TO FS TO

Support moment

Hip extensor

Knee extensor

Ankle extensor

Figure 1: Moments of force during ramp ascent. The first step (leftmost) was done while on a level surface. The rightmost step was produced during the second step on the ramp. (TO=toe-off, FS=foot-strike) Figure 2 shows the powers produced by the same subject as in Figure 1. The ankle powers during the step on the ramp were essentially the same as level walking. There was an initial burst of dorsiflexor activity followed by plantar flexor negative then positive work. The knee powers for the step on the ramp illustrated in Figure 2 have the identical pattern to those reported by Winter (1991) for level walking. Each of the K1 to K4 phases was present. The subject adjusted his stride by removing phase K1 and K2. The hip powers during level walking are usually more variable person-to-person then the knee and ankle moments. This situation was also true for ramp ascent. Phases H1, H2 and H3 were usually present but typically of lower amplitude then the step

Po

wer

(w

atts

)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Time (seconds)

-500.

-250.

0.

250.

500.

-250.

0.

250.

-250.

0.

250.

500.

Trial: RUAP03

FS TO FS TO

Hip powers

Knee powers

Ankle powers

Figure 2: Hip, knee and ankle moment powers during ramp ascent. Data are from same subject and trial as Figure 1. before the ramp. This corresponds to the lower magnitudes of the hip and support moments. SUMMARY The lower extremity’s moments during ramp ascent were essentially the same as those that occur during level walking. The major difference was the reduction of the support moment mainly due to reduced hip moments and their powers. It can be concluded that persons with weakened hip musculature should be able to negotiate ramp ascent. REFERENCES Robertson, D.G.E., Ellwood, D.M. (1995).

Proceedings of ISB 15, 774-775. Winter, D.A., Robertson, D.G.E. (1978).

Biological Cybernetics, 29, 137-142. Winter, D.A. (1991). Biomechanics and

Motor Control of Human Gait. 2ndEd.,Waterloo:Waterloo Biomechanics.