Effect of Speed and Experience on Kinetic and Kinematic Factors During Exercise on a Stair-Climbing Machine

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1 Journal of Sport Rehabilitation, 1996, 5, O 1996 Human Kinetics Publishers, Inc. Effect of Speed and Experience on Kinetic and Kinematic Factors During Exercise on a Stair-Climbing Machine Jiping Shih, Y. Tai Wang, and Manssour H. Moeinzadeh The purpose of this project was to explore the interaction between kinematic and kinetic factors and to investigate whether this relationship was affected by different speed conditions when subjects exercised on stair-climbing machines. A secondary purpose was to determine if there were any differences in kinematic and kinetic factors between experienced and inexperienced subjects. The kinematic parameters included hip angle, knee angle, and pedal angle. The kinetic parameters were maximum force applied on the pedals, maximum force applied on the handrails, maximum hip moment, and maximum knee moment. Data from a two-way (Speed x Experience) analysis of variance suggested that there were significant differences in maximum force applied on the pedal, maximum force applied on the handrail, and maximum hip moment across the speed and experience conditions. In all the testing conditions, using a stair-climbing machine had a smaller impact force on the feet than was found in a previous study that examined impact force for fast walking on a level surface. Since the 1980s, more and more people have become interested in using exercise devices to improve health and fitness. Weight training equipment, cycle ergometers, rowing machines, treadmills, and stair-climbing machines are commonly used. Stair climbing is the fastest growing form of aerobic exercise in the United States; millions of people work out on electromechanical stair-climbing machines at home and in health clubs across the country. Normal gait is characterized by the smoothness of displacement of the body's center of gravity along the progression path, as a result of perfect synchronization of the lower limb joint movements during the stance and swing phases. It has been shown that during heel strike, the vertical force component acting on the foot rises from zero to % of body weight, depending on gait velocity (10). The same study showed that when pace was increased from walking (stride length 76 cm) to running (stride length 107 cm), the total impact load increased more than 73%, J. Shih is with the Recreation, Physical Education and Dance Department, 274 Lombardi Recreation Building, University of Nevada, Reno, NV Y.T. Wang is with the Department of Health and Human Performance, Auburn University, Auburn, AL M.H. Moeinzadeh is with the Department of General Engineering, University of Illinois at Urbana-Champaign, Urbana, IL

2 Stair-Climbing Machine 225 almost 200% of body mass. From a mechanical viewpoint, using a stair-climbing machine is quite different from level walking and stair climbing (1-4,9). The differences are reflected by changes in joint range of motion and changes in the impact forces and moment applied on each joint in the lower extremities (4). The force acting on the joints is highly related to the production of moments about the joints. Force platform and photographic techniques have been described to calculate reaction forces at the hip joint (8) and at the knee joint (6) during walking. People have different abilities to absorb impact; one study (1 1) measured the capability of the human shock absorbing system to attenuate input dynamic loading during gait and concluded that healthy subjects definitely possessed a more efficient shock-absorbing capacity than did subjects with joint disorders. Another study (4) showed that shock waves invading the human musculoskeletal system may be generated not only at heel strike but also at the metatarsal strike. Although stair-climbing machines provide a flexible and convenient way to exercise, their effectiveness and safety from a biomechanical standpoint have not been investigated. No objective measures have been used to determine the impact forces and moment applied to each joint, and many questions remain answered. In order to evaluate and improve the design of these machines, it was important to investigate the kinematic and kinetic characteristics of subjects when exercising on a stair-climbing machine. An understanding of the kinetics and kinematics of using stair-climbing machines and the relationship between these variables may lead to individual, specific guidelines for exercise. The purpose of this project was to explore the interaction between kinematic and kinetic factors and to investigate whether this relationship was affected by different speed conditions when subjects used stair-climbing machines. A secondary purpose was to determine if there were any differences in terms of kinematic and kinetic factors between experienced and inexperienced subjects. Methods Twelve healthy males age years (mean = 24.9 k 5.48 years) who used stairclimbing machines were recruited from the University of Illinois at Urbana- Champaign campus to serve as subjects for this study. Each subject was given a written exercise history questionnaire. Subjects were placed in either the experienced or the inexperienced category depending upon their answer to the first question: "How often you use the stair-climbing machine during a week?'seven subjects were in the experienced group and 5 were in the inexperienced group. A StairMaster 4000PT stair-climbing machine was used in this study. It was equipped with a pair of foot pedals and a microcomputer that monitored the climbing performance of the subject and displayed exercise time, climbing speed, and distance. The four speed conditions were from 43 to 95 steps per minute (each step equivalent to 8 in.). Data Collection and Analysis Elgons (electronic goniometers) were used in this study to collect kinematic data. Elgons were placed over the hip joint, knee joint, ankle joint, and both right and left pedal, for a total of five elgons. Output voltage signals were immediately converted and recorded by a computer; thus, the angles of the hip, knee, and ankle

3 I I i I 226 Shih, Wang, and Moeinzadeh joints and of the right and left pedals were collected as shown in Figure 1. Two force transducers were placed on the pedals of the StairMaster 4000PT, so the impact force applied by each subject was recorded, thereby allowing us to calculate the forces and moment in each joint. Based on the data collected by elgons and force transducers, a sagittal plane rigid-body-linked segment analysis was used to determine joint kinetic parameters. This is commonly used (13) to characterize gait. Maximum force applied on the pedals, maximum force applied on the handrails, maximum hip moment, and maximum knee moment were normalized (12) to body mass. The kinematic data (angle of pedals, ankle, knee, and hip) were collected by computer through an analog-to-digital (AD) board, as shown in Figure 1. Procedure and Treatment of Data The experimental procedure, which consisted of collecting kinematic and kinetic records, is presented in a flow chart in Figure 2. A mean two-way (Speed x Experience) ANOVA was used to determine the differences of all the dependent variables across the speed and experience condi- Figure 1 - Sagittal view of a subject. HA = hip angle; KA = knee angle; PA = pedal angle; FH = force applied to handrails; MM = hip moment; KM = knee moment; FP = force applied to pedals.

4 Stair-Climbing Machine I c= Climbing Movement I Testing Conditions Force Transducer Kinematic + Data Kinetic Data Data Analysis Figure 2 -Flow chart of experimental procedure. tions. The independent variables were the four speed and two experience conditions. The dependent variables were the following kinematic and kinetic parameters. Kinematic parameters Maximum hip extension angle (HAmax) Maximum knee extension angle (KAmax) Minimum pedal angle (PAmin) Kinetic parameters Maximum force applied on the pedallbody mass (FPmax) Maximum force applied on the handrailslbody mass (FHmax) Maximum hip moment/(body mass) (HMmax) Maximum knee moment/(body mass) (KMmax) Joint and Pedal Angle Results and Discussion Three kinematic variables were used to evaluate the subjects' movement patterns: HAmax, KAmax, and PAmin. The kinematic variables showed that inexperienced subjects did not fully extend their hip joints (180 ), although experienced subjects

5 Shih, Wang, and Speed 2 Speed 3 Speed 4 I Speed Figure 3 - HAmax by main effects of experience and speed. 1 1 did (Figure 3). The average HAmax for experienced subjects was 178.9", 7.4% higher than that of inexperienced subjects. Any simple forward-leaning motion of the trunk can create a moment on the lumbar region that is as large as when a heavy weight is held close to the body (7). The average HAmax for experienced subjects was higher than for inexperienced subjects, which means that inexperienced subjects may have had more potential risk of injury of the lumbar region, although they applied a lower force on the pedals. It was apparent by viewing the video recording that inexperienced subjects had a difficult time maintaining speed during the lower speed condition exercises. PAmin values were the lowest values in the lower speed conditions (Speed 1 and Speed 2). PAmin increased with higher speed in both experienced and inexperienced subjects (Figure 4). In particular, some subjects repeatedly bumped the pedal into the ground. There was no significant r.5) in KAmax crossing the four speed conditions and two experience conditions (Figure 5). The average KAmax for experienced subjects was 179.7" and for inexperienced subjects 180.3". Impact Force and Moment Four kinetic variables were used to evaluate the subjects' impact force and moment: FPmax, FHmax, HMmax, and KMmax. FPmax increased as speed increased (Figure 6). The average FPmax value for experienced subjects was Nlkg, which was lower than a previous study's (12) impact force data of 12.5 Nlkg for a fast walk (cadence stepstmin). The average FPmax value for inexperienced subjects was 9.58 N/kg. FPmax in experienced subjects was 14.9% higher than that for inexperienced subjects, because inexperienced subjects tended to lean forward on the handrails to decrease their maximum force applied on the pedal.

6 Stair-Climbing Machine Speed 1 Speed 2 Speed 3 Speed 4 Speed Figure 4 - PAmin by main effects of experience and speed.. -- Speed 1 Speed 2 Speed 3 Speed 4 Figure 5 - KAmax by main effects of experience and speed. FHmax was decreased at higher speed conditions in both experienced and inexperienced subjects (Figure 7). The average FHmax value for inexperienced subjects was 59.3% higher than that for experienced subjects. This difference in FHmax, along with the difference in HAmax between experienced and inexperienced subjects, is another explanation for the lower FPmax of inexperienced subjects.

7 Shih, Wang, and Moeinzadeh Speed 1 Speed 2 Speed 3 Speed 4 Speed Figure 6 - FPmax by main effects of experience and speed. Speed 1 Speed 2 Speed 3 Speed 4 Speed Figure 7 - FHmax by main effects of experience and speed. HMmax had a different trend with higher speed conditions between experienced and inexperienced subjects (Figure 8). HMmax decreased at higher speed conditions in inexperienced subjects and increased at higher speed conditions in experienced subjects. In the higher speed conditions, FHmax values for inexperi-

8 Stair-Climbing Machine - z & 1 $ E 5: n Speed 1 Speed 2 Speed 3 Speed 4 Speed Figure 8 - HMmax by main effects of experience and speed. enced subjects decreased. The average HMmax value for inexperienced subjects was % higher than for experienced subjects. The average KMmax value for experienced subjects was 1.2 N. mlkg, which is slightly higher than a previous study's (12) data of 1. I N. m/kg for fast walking (cadence = stepslmin). The average KMmax value for experienced subjects was 1.0 N. mlkg, as showed in Figure 9. Suggestion to Users Handrails are very important to help people keep their balance when using a stairclimbing machine, especially inexperienced users. In this study, inexperienced subjects tended to lean forward on the handrails. Individuals who use stair-climbing machines should use the handrails to help maintain balance rather than to support body weight; users need to keep the whole body erect instead of leaning forward. Using the handrails correctly should help stair-climbing machine users, especially inexperienced users, reduce forward lean, which is especially important for persons with low back problems. Greater angles of forward lean reduce strength capability of the trunk musculature and increase stress to the lumbar region (5), increasing the probability of low back pain or back injury. Conclusion There were four major findings of this study. First, we found significant differences in FPmax, FHmax, and HMmax crossing the four speed conditions and between experienced and inexperienced subjects (p <.01). As speed increased, there was an increase in force applied on the pedal in both inexperienced and experienced subjects. Second, PAmin and HAmax were the two main kinematic parameters that

9 Shih, Wang, and Moeinzadeh speed Figure 9 - KMmax by main effects of experience and speed. showed significant difference between inexperienced and experienced subjects (p <.01). subjects tended to lean forward on the handrails, and they had lower FPmax and higher FHmax than experienced subjects. The third finding was that the use of handrails was critical to decrease impact force and moment in the knee joint, but this increased the force applied on the handrail and the moment in the hip joint. Fourth, walking on a stair-climbing machine produced smaller impact force on the feet than was found in a previous study's (12) impact force data for fast walking (cadence = stepslmin) on a level surface. References 1. Andriacchi, T.P., G.B. Andersson, R.W. Fmier, D. Stem, and J.O. Galante. A study of lower-limb mechanics during stairclimbing. J. Bone Joint Surg. (American) 62(5): , Cavanagh, P.R., and R.J. Gregor. Knee joint torque during the swing phase of normal treadmill walking. J. Biomech. 13: , Kyle, C.R., and V.J. Caiozzo. Acomparison of the effect of external loading upon power output in stair climbing and running up a ramp. Eur: J. Appl. Physiol. 51(4):99-103, Loy, D.J., anda.s. Voloshin. Biomechanics of stair walking andjumping. J. Sports Sci , Marras, W.S., and G.A. Mirka. Trunk strength during trunk motion. Hum. Factors 31(6): , Monison, J.B. The mechanics of the knee joint in relation to normal walking. J. Biomech. 3:51-61, 1970.

10 Stair-Climbing Machine Park, K.S., and D.B. Chaffin. A longitudinal study of low-back factors. Am. Ind. Hyg. Assoc. J , Paul, J.P. Load actions on the human femur in walking and some resultant stresses. Experimental Mechanics 111, pp , Shinno, N. Analysis of knee function in ascending and descending stairs. Med. Sport 6: , Stanish, W.D. Injuries and accidents overuse syndrome. Med. Sci. Sports Exerc. 16(1): 1-7, Voloshin, A., J. Wosk, and M. Brull. Force wave transmission though the human locomotor system. J. Biomech. Eng , Winter, D. Biomechanics and Motor Control ofhuman Gait. Waterloo, ON: University of Waterloo Press, Winter, D. Biomechanics and Motor Control of Human Movement. New York: Wiley, Acknowledgments The study was supported by StairMaster-Randal Sports/Medical Products, Inc. We thank the subjects for their cooperation.

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