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Effects of Functional Ability and Training on Chair-Rise Biomechanics in Older Adults

^a Geriatric Research, Education and Clinical Center, Department of Veterans Affairs Medical Center, Ann Arbor, Michigan
^b Division of Geriatric Medicine, Department of Internal Medicine,
^c Institute of Gerontology, The University of Michigan, Ann Arbor
^d Division of Kinesiology, The University of Michigan, Ann Arbor

Neil B. Alexander, Division of Geriatric Medicine, Department of Internal Medicine, The University of Michigan, 1111 CCGCB, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-0926 E-mail: nalexand{at}umich.edu.

Decision Editor: John E. Morley, MB, BCh

	Abstract

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Background. Difficulty in rising from a chair is common in older adults and may be assessed by examining the biomechanics of the rise. The purposes of this study were (i) to analyze the biomechanics of rise performance during chair-rise tasks with varying task demand in older adults with varying rise ability and (ii) to determine whether a strength-training program might improve chair-rise success and alter chair-rise biomechanics, particularly under situations of increased task demand.

Methods. A training group (n = 16; mean age, 82 years) completed a 12-week strength-training regimen while a control group (n = 14; mean age, 84 years) participated in a seated flexibility program. Outcomes included the ability to complete seven chair-rise tasks, and, if the chair-rise tasks were successful, the biomechanics of these rises. Chair-rise task demand was increased by lowering the seat height, restricting the use of hands, increasing rise speed, and limiting foot support.

Results. At baseline, increased chair-rise task demand generally required increased task completion time, increased anterior center of pressure (COP) placement, increased momentum, increased hip flexion, and increased hip and knee torque output. Those unable to rise at 100% knee height without the use of their hands (task NH-100), compared with those able to rise during task NH-100, followed this pattern in requiring increased time, more anterior placement of the COP, and increased hip flexion to rise in the least demanding tasks allowing the use of hands. However, the unable subjects generated less momentum and knee torque in these tasks. At 12 weeks, and compared with baseline and controls, the training group demonstrated changes in chair-rise biomechanics but no significant changes in rise success. The training subjects, as compared with the controls, maintained a more posterior COP, increased their vertical and horizontal momentum, maintained their knees in greater extension, and maintained their knee-torque output.

Conclusions. These data demonstrate that subtle yet significant changes can be demonstrated in chair-rise performance as a result of a controlled resistance-training program. These biomechanical changes may represent a shift away from impairment in chair-rise ability, and, although the changes are small, they represent how training may reduce rise difficulty.

DIFFICULTY in rising from a chair is common in older adults ⁽¹⁾. This difficulty often occurs with demanding chair-rise tasks, such as when the seat is lowered or highly compressible or when hand use is restricted ^(2)(3)(4)(5). To rise under these difficult situations, older adults often alter their rise strategy. Placing the body center of mass over the feet (e.g., by flexing the trunk forward) is one strategy used by chair-rise–impaired older adults to rise under more demanding situations ^(3)(5)(6). Placing the center of mass forward, along with slowing rise speed, may minimize momentum or slow the rate of torque development and thus facilitate postural control while rising ⁽⁷⁾. Another strategy, where higher trunk momentum is generated and more rapid knee extension is deployed, would presumably be found more often in younger adults and less impaired older adults who are better at maintaining postural control ⁽⁷⁾. Yet another option would be to use elements of both strategies ⁽⁸⁾. Older adults are less able to generate momentum (especially vertically) during the rise, likely due to reduced leg strength ⁽⁹⁾. Ultimately, in rise-impaired older adults, the most critical factor determining rise ability when chair-rise demand increases may be leg strength and not postural control ⁽¹⁰⁾. Decreased leg strength is associated with alterations in chair-rise biomechanics, such as increased trunk flexion and decreased center of mass acceleration ⁽¹¹⁾. Decreased leg strength becomes particularly important as the strength requirements of the rise task increase. The knee torque required to rise is nearly 100% of the available knee strength in healthy older adults at low seat heights ⁽¹²⁾ and is nearly 100% of the available knee strength in disabled older adults at the lowest chair height from which they are able to rise successfully ⁽¹³⁾.

The purposes of this study were (i) to analyze the biomechanics of rise performance during chair-rise tasks with varying task demand in more disabled older adults with varying rise ability and (ii) given the importance of leg strength in determining chair-rise success and rise strategy, to determine whether a strength-training program might improve chair-rise success and alter chair-rise strategy, particularly under situations of increased task demand. We increased the chair-rise demand by lowering chair height, by asking subjects to increase movement speed, by not allowing subjects to use their hands, and by reducing the support surface allowed for the feet. Some of these tasks simulate typical environmental challenges (such as lowering the seat height), and others presumably increase the required leg strength (no-hands rise) or required postural control (reduced-support rise). For the first goal (using baseline data for the baseline analysis), we hypothesized that with increased task demand, task performance biomechanics would change in a characteristic manner (more time required for completion, increased anterior center of pressure [COP] movement, increased momentum, increased body angle motion, and increased joint torque requirements). We also hypothesized that older adults with lower rise ability, defined by the inability to rise without the use of hands at a standard seat height, would increase their trunk flexion and slow their momentum, particularly under conditions of increased rise demand. In regards to our second goal (using baseline and post-intervention data for the intervention analysis), we hypothesized that subjects undergoing strength training would (i) become more successful than the controls in completing more demanding chair-rise tasks and (ii) when successful, have less difficulty in rising, as indicated by characteristic changes in chair-rise biomechanics (decreased rise time, increased momentum, decreased trunk flexion, and decreased anterior displacement of the COP).

	Methods

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Subjects
Volunteers aged 65 and over were recruited from a local congregate housing facility. Medical exclusions included lower-extremity hemiplegia (hemiparesis was allowed) or amputation, blindness, acute inflammatory or infectious illness, dementia [Folstein Mini-Mental Status Examination score less than 24 ⁽¹⁴⁾], or depression [short-form Geriatric Depression Scale >5 out of 15 ⁽¹⁵⁾]. Eligible subjects had to complete the least challenging chair-rise task of rising from a chair with the seat adjusted to 140% of floor to popliteal fold distance (i.e., 140% floor-to-knee height [140% FKH]). Subjects could not be currently involved in a formal exercise program. All subjects had to be able to participate in a group exercise setting. Subjects were allocated to a strength-training or a control group on the basis of age, gender, and baseline functional ability [Katz Activities of Daily Living (ADL) ⁽¹⁶⁾] using a computer-based matching method designed to minimize experimental group differences.

Chair-Rise Testing Protocol
All subjects were tested at baseline and following 12 weeks of exercise. Subjects rose from an adjustable instrumented laboratory chair, designed to vary in seat height, in the presence or absence of armrests. The seat height was adjusted to 140%, 100%, and 60% FKH. Armrests were attached to the chair at a height that ensured the same upper extremity position for each subject (15° shoulder extension and 90° elbow flexion). When rising without the armrests, subjects folded their arms across their chest. To reduce the support surface and to provide a challenge to postural control, subjects placed their feet across an 11-cm wide beam, mounted onto floor-mounted force plates, so that their lateral malleoli were aligned with the edge of the beam.

Subjects were asked to perform seven chair-rise tasks, at the three seat heights, with (H) or without (NH) the use of hands and without the use of hands as fast as possible (F) or with feet on the beam (B). The tasks were ordered according to seat height and in anticipated order of increasing demand: H-140, NH-140, H-100, H-60, NH-100, NH-100-F, and NH-100-B. Subjects began each rise from the same initial position with the trunk vertical, ischial tuberosities supported by the seat, and the ankle dorsiflexed at 10°, whereas initial knee and hip angles varied with chair height. For all but the F rise, subjects were asked to rise at a comfortable speed. Rise success was defined as rising continuously to a standing position without moving the feet, rising from the seat and falling back, scooting forward on the seat, or releasing the arms from the strap when used for the NH condition. If successful, subjects performed three trials in each condition; the second trial was typically used for data analysis. To dichotomize the group by chair-rise functional ability for the baseline analysis, subjects were categorized as able or not able on the basis of their ability to perform the NH-100 task (see below). Difficulty in rising from a standard chair without the use of arms (akin to NH-100) has recently been found to be effective in distinguishing subjects at high (vs low) risk for ADL dependence ⁽¹⁷⁾.

Markers were placed on the left fifth metatarsal head, lateral malleolus, lateral femoral condyle, greater trochanter, acromion process, lateral humeral epicondyle, and ulnar styloid process. For simplicity, we report only the kinematics at key joints where there were major kinematic changes, namely at the knee and hip. Three 60-Hz video cameras were used with a motion analysis system for kinematics. Movement time was determined by the motion of the shoulder joint marker. Chair rise began with the onset of horizontal motion of the shoulder marker and ended when the shoulder marker reached 98% of the standing height. The kinematic data were smoothed and differentiated using a cubic spline ⁽¹⁸⁾. By convention, increased joint angles represent increased extension; thus, decreased knee and hip angles represent increased knee and hip flexion, respectively. Reaction force data were obtained from a force plate under the feet and on the chair seat. Force data were sampled at 120 Hz and were filtered using a recursive 10th order Butterworth filter with a 7–Hz, low-pass cut-off frequency. The COP was calculated from the force data and referenced to the ankle so that an increased positive value represented a more anterior location. Using anthropometric data for body segments determined from subject height and weight, torques about the hip, knee, and ankle joints were calculated using the ground reaction force and kinematic data ⁽¹⁹⁾. Torques were normalized by body weight and height. Kinematic and COP data were taken at liftoff. Momentum and torque were taken at their maxima, which may not necessarily have occurred at liftoff.

Exercise Protocols
Resistance training.-- Both groups met 1 hour per day, 3 days per week.

The resistance-training intervention included four HydraFitness (Hydra-Fitness Industries, Belton, TX) equipment exercises: hip abduction, knee extension/flexion, stair climbing, and squatting. The HydraFitness equipment used hydraulic resistance that allowed only concentric muscle contractions and had six levels of intensity (three for the stair climber). Two other resistance exercises included weighted chair rise and ankle dorsi/plantarflexion (LifePlus Footdeck Sport, Ann Arbor, MI). In the weighted chair-rise task, subjects wore a weighted vest that progressed from 0 to 10 lb at 5-lb increments. Once the subject completed the chair rise progression using the hands, the subject followed the same progression without using the hands.

Control exercises.-- The control group participated in a series of seated neck, trunk, arm, leg, and foot flexibility exercises.

Baseline Analysis
For the baseline analysis, the training and control subjects were analyzed together (n = 30). A two-way ANOVA was used to examine symmetric 2 x 2 comparisons (i.e., seat height x hand use [140 vs 100 with or without hands] and ability group [able vs unable at H-140 and H-100]). Because of reduced rise success rates in the H-60, NH-100-F, and NH-100-B tasks, separate repeated measures (RM)-ANOVA with pairwise post-hoc comparisons (Fisher's PLSD) were used to examine the effect of seat height (H-140 vs H-100 vs H-60), rise speed (NH-100-F vs NH-100), and beam use (NH-100-B vs NH-100). Note that in these last analyses, the number of subjects varies according to the number able to perform the most difficult task under analysis.

Intervention Analysis
For the intervention analysis, training subjects (n = 16) and controls (n = 14) were analyzed separately. Group differences in rise ability were analyzed using Fisher's exact test. For each chair rise task, RM-ANOVA was used for all kinematic, COP, momentum, and torque analyses, focusing on the group x time effect (i.e., the interaction of group [training vs control] and time [baseline vs 12 weeks] effects).

	Results

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Subjects
Forty-two volunteers were initially screened, but after three were excluded for medical reasons, 39 subjects were allocated to participate. Nine subjects dropped out (seven within 6 weeks), leaving 30 subjects to complete the 12-week program. Five of the drop-outs had acute illness (e.g., influenza, urinary tract infection), and four of the drop-outs had increased musculoskeletal pain that resolved after discontinuation of the exercise (three in the training group and one in the control group). Women predominated in both groups with a mean age of 82 years in the training group and 84 years in the control group (Table 1 ). No significant differences were noted between groups (Table 1 ).

Effect of ability: tasks H-140 and H-100.-- When compared on two tasks that most able and unable subjects could complete (H-140 and H-100), the unable subjects took longer to complete the tasks, placed their COP further anterior, utilized less vertical and horizontal momentum, and used a smaller hip angle (more hip flexion) and lower knee torque (all p < .005 by two-way ANOVA) (Fig. 1). Smaller effects were seen in a tendency to increase hip torque (p = .06) in the unable subjects versus the able subjects. Independent effects were also seen in seat height, in that the 100% (vs 140%) rises required more time, further anterior COP placement, increased vertical momentum, less knee and hip angle (more knee and hip flexion), and increased knee and hip torque (all p < .0005 except p < .05 for time and COP by two-way ANOVA). Interaction effects (seat height x group) were seen in increased completion time (p < .05) and trends in less vertical momentum (p = .06) and knee torque (p = .08) (i.e., the unable subjects disproportionately increased their rise time and tended to generate disproportionately less vertical momentum and knee torque as the seat height was lowered).

View larger version (82K): [in this window] [in a new window]   Figure 1. Comparison of able versus unable subjects during the performance of H-140 (use of hands, seat height at 140% floor-to-knee height) and H-100 (use of hands, seat height at 100% floor-to-knee height) tasks. A, Mean (±SD) rise time (seconds); mean (±SD) placement of center of pressure (cm) with respect to the ankle at liftoff. B, Mean (±SD) maximum horizontal and vertical momentum (kg·m/s). C, Mean (±SD) maximum knee and hip angle (degrees). D, Mean (±SD) normalized maximum joint torque at the knee and hip. See text for description of results (n = 17 able; n = 13 unable).

View larger version (84K): [in this window] [in a new window]   Figure 2. Comparison of the performance of H-140 (use of hands, seat height at 140% floor-to-knee height), NH-140 (no use of hands at 140%), H-100 (use of hands, seat height at 100% floor-to-knee height), and NH-100 (no use of hands at 100%). A, Mean (±SD) rise time (seconds); mean (±SD) placement of center of pressure (cm) with respect to the ankle at liftoff. B, Mean (±SD) maximum horizontal and vertical momentum (kg·m/s). C, Mean (±SD) maximum knee and hip angle (degrees). D, Mean (±SD) normalized maximum joint torque at the knee and hip. See text for description of results (n = 18).

View larger version (32K): [in this window] [in a new window]   Figure 3. Percent of subjects within each group able to complete each chair-rise task before (baseline) and after (12 weeks) the training intervention. A, training intervention group. B, control intervention group.

View larger version (25K): [in this window] [in a new window]   Figure 4. Comparison of training and control groups for mean (±SD) A, movement (rise) time and B, center of pressure change (cm) from baseline to 12 weeks according to each chair-rise task. A positive (or less negative) time change reflects a reduction in time from baseline to 12 weeks. A positive (or less negative) value reflects center of pressure placement more posterior from baseline to 12 weeks; a negative value reflects center of pressure placement more anterior.

Momentum.-- Vertical. Mean maximum vertical momentum tended to increase for most tasks from baseline to 12 weeks, although only significantly for NH-100 (p < .05). This increase in vertical momentum was more prominent in the training group than in the controls for the more challenging tasks (i.e., group x time, p < .05 for NH-100). Fig. 5 displays the change in mean vertical momentum (i.e., baseline minus 12 weeks): More negative values suggest bigger increases in vertical momentum, and positive values suggest reductions in momentum. Horizontal. Mean horizontal momentum differed little between the groups and from baseline to 12 weeks. However, for two challenging tasks, NH-100 and NH-100-F, horizontal momentum increased in the training group but decreased in the controls (group x time, p < .05). Fig. 5 shows the change in horizontal momentum from baseline to 12 weeks, with negative representing momentum improvements and positive representing momentum reductions.

View larger version (23K): [in this window] [in a new window]   Figure 5. Comparison of training and control groups for mean (±SD) momentum change (kg·m/s) from baseline to 12 weeks according to chair-rise task. A negative value reflects an increase in momentum from baseline to 12 weeks; a positive value represents a decrease. A, vertical momentum; B, horizontal momentum.

View larger version (22K): [in this window] [in a new window]   Figure 6. Comparison of training and control groups for mean (±SD) angular lower extremity kinematic change (degrees) from baseline to 12 weeks according to chair-rise task. A negative value reflects a decrease in flexion (more extension) from baseline to 12 weeks; a positive value represents increased flexion (less extension). A, knee kinematics; B, hip kinematics.

View larger version (22K): [in this window] [in a new window]   Figure 7. Comparison of training and control groups for mean (±SD) normalized maximum torque from baseline to 12 weeks according to chair-rise task. A less positive (or negative) value reflects increased maximum torque from baseline to 12 weeks; a more positive value represents decreased maximum torque. A, knee torque; B, hip torque.

	Discussion

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This ability to generate momentum and torque seems particularly relevant for the more functionally disabled subjects, those unable to rise from a standard height without the use of their hands (task NH-100). The unable subjects, when compared with the able subjects (those able to complete NH-100), followed the pattern above in requiring increased time, more anterior placement of the COP, and increased hip flexion to rise in the least demanding tasks allowing the use of hands (tasks H-140 and H-100). However, the unable subjects generated less momentum and knee torque in these tasks. The unable subjects appeared to be especially challenged by the move from H-140 to H-100, causing disproportionately prolonged rise times and trends in disproportionate decreases in vertical momentum and knee torque. The unable subjects may have been concerned with maintaining postural control, thus limiting their momentum. Or, given the relatively low hip torque requirements of the hands tasks (H-140 and H-100) compared with the no-hands tasks (NH-140 and NH-100), the success of the unable subjects in the H versus NH tasks may relate to lack of strength. The small sample size (and subsequent small group clinical differences) and the lack of quantitative standing postural control and limb strength measurements limit further conclusions.

The performance of the unable subjects is consistent with models of chair-rise performance in impaired adults. With increased age and increased functional disability, increased trunk flexion and hip moments ⁽³⁾⁽⁶⁾ are thought to be part of a strategy to maintain a more stable rise pattern ⁽⁷⁾. As part of this pattern, horizontal momentum is constrained, as was true of the unable subjects, to maximize postural control ⁽⁷⁾. As further evidence of their constrained, stable pattern, the unable subjects maintained a more anterior COP and also limited their vertical momentum.

The lack of success in performing certain tasks and the biomechanical strategies of those who did succeed give insight into the strength and postural control requirements of the tasks. The lack of beam-task (NH-100-B) success (n = 7 successful) was likely a marker of postural control difficulty, given that the relatively larger hip and knee torques required were generally within the available torque output as demonstrated by the larger subject subgroup completing the fast rise task (NH-100-F, n = 16 successful). Of all the tasks, the beam task also required the highest horizontal momentum (i.e., the highest horizontal velocity of the center of mass). Stability during a task is determined not only by center of mass position, but also by its velocity at that given position ⁽²⁰⁾. The beam task required subjects to generate substantial horizontal velocity to propel the center of mass to a position over a reduced surface while not exceeding the range of horizontal velocities that would ensure dynamic balance while on the beam. Presumably the beam constrained the subject's ability to generate torque to arrest this increased horizontal momentum. In this case, the anterior location of the COP with respect to the ankle did not necessarily indicate enhanced stability.

Common biomechanical performance strategies were demonstrated among the different task demand situations but may have had different underlying mechanisms. Compared with higher seat levels, the relatively high hip and knee flexion angles used in rising from the lowest position (H-60) resulted in markedly increased hip and modestly increased knee torque generation. Compared with tasks where hand use was allowed (e.g., H-100), the relatively high hip flexion angles used in the no-hand tasks (NH-100, NH-100-F, and NH-100-B) also resulted in increased hip torque output. The increased torque requirements with lowered seating are not surprising, given that decreased seat height is known to increase leg (particularly knee) torque requirements ⁽²¹⁾. Furthermore, leg (particularly knee) strength is thought to be the limiting factor in determining rises from low seat heights in frail older adults ⁽¹³⁾. On the other hand, the pronounced hip flexion angle and torque during the NH beam task is consistent with a hip strategy used to maintain balance in reduced-support surface conditions ⁽²²⁾ (i.e., the hip flexion used in the beam task reflects a postural control strategy). In the NH tasks, there are a number of reasons for the increased hip flexion and torque. First, compared with chair rises with the use of hands, chair rises without the use of hands require higher leg torque ⁽⁶⁾, which facilitates those with limited leg strength to rise. In addition, compared with chair rises with hands, chair rises without hands also bring the COP more posterior, thereby stressing the postural control of the rising subject ⁽⁶⁾. Similarly, there is a relative increase in momentum, particularly horizontal, in the no-hands tasks compared with the hands tasks, thereby requiring sufficient postural control to arrest this momentum. Thus, the biomechanical strategies used by the functionally impaired older adults in the present study probably reflect their response to the strength and postural control demands of the tasks, and thus likely reflect their own impaired strength and postural control abilities ⁽¹⁰⁾. Unfortunately, hand force data were not available to help further understand the rise strategies used. Note also that the present study [as in Gross and colleagues ⁽¹¹⁾] finds that hip kinematics and torques, as compared with the knee, show more variability by task demand and subject functional ability, suggesting that future chair rise studies should also consider the importance of hip strength, particularly among the more disabled.

Intervention Analysis
Strength-training participants demonstrated a change in their chair-rise biomechanics compared with controls undergoing seated flexibility training. To our knowledge, this is the first study to demonstrate, in relatively impaired older adults, strength-training–related alterations in the biomechanics of an ADL task in a controlled study. The training did not significantly improve the success in rising from a chair or chair rise time, but there was a trend for more training than control subjects to become able to rise, particularly for the more demanding tasks. The biomechanical change was directed away from a larger trunk flexion (stabilization) strategy ⁽⁷⁾ and more toward a higher momentum (momentum transfer) strategy. The training group, as compared with the controls, maintained a more posterior COP, increased their vertical and horizontal momentum, maintained their knees in greater extension, and maintained their knee torque output. These biomechanical changes are similar to those seen in the able subjects versus the unable subjects (see Baseline Analysis) and may represent a shift away from impairment in chair-rise ability. Although the changes are small, they represent how training may reduce rise difficulty, particularly if continued on a long-term basis.

The training subjects generated more momentum, perhaps a function of improved strength and postural control. Furthermore, the findings of training-induced changes in knee extension and knee torque (vs hip motion or torque) suggest local improvements in knee but not hip strength. Unfortunately, we cannot corroborate the contribution of improved strength and postural control because no independent objective measures of leg strength and standing balance were available.

A number of factors may have blunted the training effect. First, the controls were involved in a group exercise program, and there is evidence that the controls tended to improve their chair-rise ability, at least as indicated by trends in rise time. The training effect might have been greater with a nonexercise control group. We chose a seated flexibility program for the control because these programs are widely used in congregate housing facilities and thus represent a community-based exercise standard. We had hoped to show more marked improvements than the small improvements [such as slight reduction in chair rise time ⁽²³⁾] resulting from these programs.

The testing protocol itself may also have blunted the training effect. The chair-rise outcome measures focused on usual performance (i.e., rising at a comfortable rate). The only capacity-oriented measure was NH-100-F, and given the lack of training focus on increasing rise speed, minimal training effect for NH-100-F should be expected. Second, the rise instructions were constrained by design to provide valid data for the torque calculations. By not allowing foot repositioning or multiple attempts, we did not allow for a wide array of self-selected rise strategies. The constraining of rise strategies may have induced the training group to increase their momentum and move in a more vertical direction. Future studies might consider alternate but perhaps controlled rise styles [e.g., with different proscribed foot positions ^(24)(25)] to analyze the effect of training on rise biomechanics.

These data demonstrate that subtle yet significant changes can be demonstrated in chair-rise performance as a result of a controlled, short-term resistance training program. The group we targeted, congregate housing older adults, represents a cohort that is still able to maintain independence but that is likely to be at risk for impending disability ⁽²⁶⁾. Future studies may consider whether longer-term resistance training will continue to maintain these changes in chair-rise biomechanics and avert frank chair-rise disability.

	Acknowledgments

 
We acknowledge the support of the Department of Veterans Affairs Rehabilitation Research and Development, National Institutes on Aging (NIA) Claude Pepper Older Americans Independence Center (AG08808), as well as NIA Grants AG10542 and AG00519, and a University of Michigan Career Development Award. The contributions of the Glacier Hills Retirement Center staff and residents are gratefully acknowledged. We thank Bill Duren, Terry O'Bannon, Kathy Jacobs, Amy Kelman, and Amy Tyler for their assistance with data collection and analysis and Becky Luebke for her assistance in resident training.

Received July 26, 2000

Accepted July 27, 2000

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