Effects of a Plyometric Training Program for 3 Children With Neurofibromatosis Type 1

Johnson, Barbara A. PT, MSPH; Salzberg, Charles L. PhD; Stevenson, David A. MD

Pediatric Physical Therapy:
doi: 10.1097/PEP.0b013e31824d30ee
Case Report

Background and Purpose: To evaluate the feasibility and safety of plyometric training and to determine the effects on motor proficiency.

Case Description: Three children with neurofibromatosis type 1, aged 5, 7, and 10 years, selected for representative ages, sexes, abilities, and outcomes participated in a 10-week plyometric training program. Outcome measures included throwing and jumping distance, performance on a self-selected goal, the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition, and the Children's Assessment of Participation and Enjoyment.

Outcomes: All participants safely completed the program. Improvements were seen in distance and consistency of throwing and jumping, performance on the self-selected goal, and bilateral coordination composite scores. Increased diversity, but not intensity of physical activity, was observed.

Discussion: A safe plyometric training program was implemented, resulting in gains in motor performance. It may be important to address personal and environmental barriers to physical activity participation to improve intensity of physical activity.

In Brief

A plyometric training program was safely implemented and resulted in gains in motor performance for 3 children with NF 1. The authors suggest that barriers to participation in physical activity may have to be addressed for these children.

Author Information

Shriners Hospitals for Children Salt Lake City (Ms Johnson and Dr Stevenson), Salt Lake City, Utah; Department of Special Education and Rehabilitation (Dr Salzberg), Utah State University, Logan, Utah; Department of Pediatrics, Division of Medical Genetics (Dr Stevenson), University of Utah, Salt Lake City, Utah.

Correspondence: Barbara A. Johnson, PT, MSPH, Shriners Hospitals for Children, Salt Lake City, Fairfax Ave and Virginia St, Salt Lake City, UT 84103 (bajohnson@shrinenet.org).

Grant Support: This research was carried out with support from a research grant from the Thrasher Research Fund, Grant # 02830.

At the time this article was written, Ms Johnson was a doctoral student at Utah State University in the Department of Special Education and Rehabilitation, Logan.

The authors declare no conflict of interest.

Article Outline
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Neurofibromatosis type 1 (NF1) is a genetic disorder with associated musculoskeletal impairments, tumors, and developmental delays.1 Secondary musculoskeletal impairments include low motor proficiency,2 weakness,3 low muscle mass, and low bone density.4 Research on physical therapy interventions for children with low motor proficiency is limited. However, increased awareness is evident in the past 10 years of the need to provide treatment to children with developmental coordination disorder. Developmental coordination disorder is a health condition in which coordination is substantially below that expected for a child's chronological age and intelligence.

Researchers have examined resistive strengthening exercise,5 core strengthening,6 aquatic exercise,7 a comprehensive balance, stretching, and strengthening program,8 and a task-specific training program for children with developmental coordination disorder9 and found improvements in strength,5 self-reported motor skill goals, improvement on a qualitative core stability assessment,6 and improvement in gross motor tasks.9 An optimal intervention should include activities to improve motor proficiency, increase muscle strength, and increase bone density to address the impairments associated with NF1.

High-impact sports that involve weight-bearing and an increase in the mechanical loading of bone are recognized as activities that can improve bone density.10 Plyometric exercise consists of high-impact activities such as hopping, jumping, bounding jumps, or throwing weighted balls. Plyometric exercise starts with a rapid stretch of a muscle, followed by a rapid shortening. Theoretically, the nervous system is conditioned to react more quickly to the stretch-shortening cycle. This type of exercise can enhance a child's speed of movement, increase power production,1114 and strengthen bone.10 Plyometric training programs have been shown to be effective in adults and pubertal children both for improving running speed and jumping ability15 and for increasing strength.16

Recent research on young children developing typically and children involved in athletics indicates that plyometric training has a large effect on improving the ability to jump1214 and run12,13 but only a small effect on improving strength.17,18 The small effect on improving strength may be explained by the differences in the mechanisms for strength gain in prepubertal children. Strength gains in young children have been attributed to intrinsic muscle adaptation and neural adaptation, since prepubertal children lack circulating androgens responsible for muscle hypertrophy.19 Researchers report that plyometric training also had a large effect on improving kicking distance14 and agility.13 If these same improvements can be seen in children with NF1, this intervention could have the potential to improve motor proficiency by improving the firing rate and motor unit recruitment of muscles.

Children with low motor competence are likely to have poor physical fitness compared with children with high motor competence.20 Since low physical fitness increases the risk of chronic diseases such as obesity, diabetes, and cardiovascular disease, this is concerning. Wrotniak et al21 reported a positive relationship between physical activity and motor proficiency. Children who completed running speed and agility tasks faster and jumped farther on the Bruininks-Oseretsky Test of Motor Proficiency, Second Edition (BOT2), were more physically active, suggesting that running and jumping are fundamental skills for participating in active games and sports. Improving physical activity is a national health initiative for children of all abilities.22 Physical activity helps to build healthy bones and muscles, to reduce the risk of chronic disease, to decrease feelings of anxiety and depression, and to improve feelings of psychological well-being in youth.23 Therefore, a program focused on motor skills that are necessary for participation in sports may improve participation in physically active recreation and leisure activities.

Children with NF1 may benefit from plyometric exercise; however, plyometric training produces dynamic movements and greater force on muscles and bones. Historically, plyometric training was deemed unsafe for youth and a predetermined level of strength was a prerequisite for participation in a plyometric program. A recent update from the National Strength and Conditioning Association (NSCA)24 indicated that this recommendation was not supported by current research or observation of everyday play activities. Young school-aged children engage in playground games and recreational sports where they run, skip, hop, jump, hurdle, and throw daily. Two professional organizations, the American Academy of Pediatrics Council on Sports Medicine and Fitness23 and the NSCA, have published position statements describing the risks, benefits, reported injuries, recommendations, and guidelines for resistive exercise in young children. The primary concerns in plyometric training of children are injury to the growth plates due to the ground reaction forces that are generated from landing activities25 or from overtraining.26 Faigenbaum and Myer27 concluded in their review that the risk of injury from resistive exercise training for children was no greater than any other sport or recreational physical activity. Most injuries reported were due to inadequate supervision, poor exercise technique, or inappropriate training load. Myer et al28 reviewed data from the US Consumer Product Safety Commission to evaluate injuries to children participating in resistive exercise training. The number of accidental injuries were highest in the 8- to 13-year-old age group, and 2/3rds were related to dropping or pinching injuries involving the hand and foot.

Despite its potential value, a specific and individualized plyometric training program to improve the motor proficiency of children with NF1 has not been the subject of research. The purpose of this multiple case report was to determine the feasibility and safety of implementing a plyometric exercise program and to evaluate the effects of plyometric training on jumping and throwing distance, motor proficiency, and participation in physical activity. We hypothesized that the plyometric training program would improve the ability of children with NF1 to throw and jump, improve motor proficiency, and improve the intensity, diversity, and enjoyment of participation in recreational physical activity. This article describes the outcomes of 3 children participating in a plyometric training program, twice a week for 10 weeks.

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Three children with NF1 were chosen to represent a spectrum of ages, sexes, abilities, and outcomes from an initial group of children receiving a plyometric training program. Assent and consent were received from the participants and their parents. Participant 1 was a 10-year 6-month-old girl; participant 2 was a 7-year-old girl, and participant 3 was a 5-year 11-month-old boy. The participants met the following inclusion criteria: (a) prepubertal child older than 5 years with a clinical diagnosis of NF1 who had been cleared to exercise by a physician, (b) whose parents expressed concerns about his or her motor abilities during clinic visits, and (c) who scored in the below average or well-below average range in one of the composite scores of the BOT-2.24 Children who had a visual impairment, an orthopedic procedure within the last 6 months, or tibial dysplasia were excluded from the study to reduce the influence of visual impairments on eye-hand coordination and the influence of surgery or musculoskeletal impairments on motor skill performance. Children younger than 4 years were not included because of limitations of the BOT2 instrument with young children, and children at greater than Tanner stage 2 classification on pubertal physical examination were excluded to rule out the influence of puberty on muscle hypertrophy and strength.

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Primary Outcome Measures

It was anticipated that the outcomes of a plyometric training program would be improvement in children's ability to jump and throw. Measures were identified that would provide a direct indicator of progress in throwing and jumping distance. The ball throw and broad jump tests29 were used to assess weekly changes in throwing and jumping distance. These 2 tests take 5 minutes to administer, can be carried out in the field, have normative reference values based on age and sex, and require a minimal amount of equipment. Criterion rated validity (intraclass correlation coefficients of 0.82 for the ball throw test and 0.99 for the broad jump test) and intrarater reliability (0.99) of both tests are high.29 Age- and sex-specific percentile values are provided and can be used to characterize performance relative to the normative population.

Since children benefit most from practicing motor tasks that are meaningful to them, each participant identified a motor goal and a method of measuring the goal was determined. The child was given verbal instruction on how to perform the motor task, allowed to practice the task, was asked how he or she thought he or she did and how he or she might improve his or her performance. At the end of the 5-minute cooldown, the child was provided 2 opportunities to perform the motor task and his or her performance from the 2 trials was recorded on the data sheet.

An additional purpose of the study was to evaluate the safety of plyometric training. A count of ground contacts (number of times the feet contacted the ground during jumping) was recorded to avoid overtraining. Ground contact times were kept within the values reported in plyometric training programs in research on children who were developing typically (50–60 at the beginning of the intervention progressing to 90–190 by the end of the intervention) for each session. A measure of perceived exertion was used to track the child's perception of intensity, and a log of any child or parent concerns related to resistive training was kept. Perceived exertion was assessed to determine whether children were exercising in the appropriate range to prevent overexertion and overtraining using the Children's Perceived Exertion Scale (PES).30 The PES is an 11-point numerical scale with 5 pictures representing youth participating at various levels of exertion. The validity of the scale was evaluated in a sample of twenty-six 10-year-old children (r = 0.70−0.77). A log of sprain/strains, muscle soreness, fatigue, safety concerns, falls, or injuries was kept to track the safety of the intervention and address any events or concerns. A count of the number of throws and the number of ground contacts during jumps was recorded.

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Secondary Outcome Measures

Standardized tests of motor proficiency and participation in physical activity were used as a gross indicator of change and were performed before and at the end of the intervention. Participants were assessed by the first author 1 week before beginning the intervention (pretest) and 1 week after the last plyometric training session (posttest). Motor proficiency was examined using the BOT2. Interrater reliability, test-retest reliability, and internal consistency of the BOT2 were moderate to strong (r > 0.80). Content validity, internal structure, and relationships with other measures of motor proficiency were also strong (r = 0.80).31 The test manual was used to calculate Z scores, and standard scores for all composite scores. The Z score was used to determine how far an individual's score fell from the age- and sex-normed scores and to document the participant's progress compared with age- and sex-matched peers. The standard scores were used to document change from pretest to posttest, to compare the participant's scores with values reported in the research literature for minimum detected change scores (those that are above the error of measurement), and to determine whether the change was considered to be clinically important (minimum important difference [MID] score).32

Generalization of the effects of a plyometric exercise program to participation in physically active recreation and leisure activities was assessed with the Children's Assessment of Participation and Enjoyment (CAPE).33 The CAPE is a standardized assessment that can be used as a research tool to provide comprehensive evaluation of activity patterns and to evaluate changes in children's participation over time. Internal consistency for the physical activity domain was established using the Cronbach coefficient α and resulted in values of 0.42 to 0.52. Test-retest reliability was 0.12 for enjoyment, 0.78 for diversity, and 0.81 for intensity. Validity was established during the item development with a literature review, expert review, and pilot testing. It was designed to be used with children with and without disabilities.33 The CAPE results in scores for diversity (the number of activities done), intensity (frequency of participation measured as a function of the number of possible activities within a category), with whom (the people the child participates with), where (the type of environment), and enjoyment (how much the child likes or enjoys doing the activity). The CAPE scores are calculated by dividing a participant's responses by the total number of responses possible for each area. A higher score reflects a more desirable outcome. Pre- and posttest scores were compared for the physical activity domain (recreation or leisure activities that are physically active).

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The intervention was delivered at each participant's home. The first author performed all outcome measures and delivered the intervention. The exercises were performed on grass or inside on a mat in an area that had sufficient room for jumping and throwing. The participants were encouraged to exercise in appropriate exercise apparel and supportive shoes. Parents were present for the exercise sessions, and the therapist provided direct supervision. The participants began the plyometric intervention after they were evaluated by their physician and had received the BOT2 and CAPE assessments. Only 1 participant received the intervention at a time. The plyometric training program followed recommendations of the NSCA and the American Academy of Pediatrics for resistive training. The intervention was carried out twice a week on nonconsecutive days for 10 weeks. The plyometric training program followed a block periodization protocol34 and consisted of two 5-week training blocks. Exercises were taught, and the load was gradually increased during the first 5-week block of training. Fifty percent of the exercises were changed, and exercise load was gradually increased again during the second 5-week training block.

Each exercise session consisted of a 5-minute warm-up of dynamic stretching exercises, administration of the ball throw and broad jump tests, 8 plyometric exercises, a 5-minute cooldown activity chosen by the child, testing of the self-selected goal, and rating on the PES. The first exercise session of the week focused on developing horizontal power, and the second session of the week focused on developing vertical power. The plyometric exercise program consisted of 1 to 2 sets of up to 15 repetitions of 4 upper extremity and 4 lower extremity plyometric exercises. Lower extremity and upper extremity exercises were alternated, and the child was given a 30-second to 2-minute rest between exercise sets. Low-intensity plyometric exercises35 were chosen on the basis of the child's ability to perform the exercise with correct technique. The baseline number of repetitions was noted, and the number of repetitions was gradually increased per individual capability to prevent post–exercise soreness or injury. Exercise load was increased by encouraging the children to jump to cones that were placed farther apart or by adding an additional riser to the bench to encourage the child to jump higher. Upper extremity exercise load was increased using graduated weighted balls or by encouraging the child to throw a longer distance. If the child could perform 2 sets of 15 repetitions of the low-intensity exercises, moderate-intensity exercises were chosen for the second training block. Table 1 describes the plyometric exercise program for participant 1.

The sessions lasted between 30 and 45 minutes. The child earned a small reward at the end of the week for completing the prescribed number of repetitions and following safety rules. Safety was assured by teaching correct technique, providing constant supervision, and counting ground contacts during jumping to avoid overuse injuries. The safety rules were dependent on the individual child's behavior and included listening to directions, not playing with the equipment between exercises, not flopping on the ground, watching the ball during throwing and catching, throwing only to the target or therapist, and paying attention to foot placement when jumping on the step to avoid falls. The therapist used an exercise log to record the warm-up activities, the 8 plyometric exercises, the number of repetitions performed, the weights of the balls, the distance or height of jumps and throws, and the self-selected cooldown activity. The PES was used to ensure that children were exercising at an appropriate intensity level.

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The equipment necessary for the plyometric intervention included a yoga mat, a set of weighted balls, a step bench with 2 risers, and a set of cones. The therapist had a notebook, with a description of the exercises, and an exercise log.

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Data Analysis

Weekly graphs of the mean throw distance and jump distance and a measure of the self-selected goal were used for data analysis. The throw and jump distances were measured in centimeters. A count value or time in seconds was measured for the self-selected goal. Four trials (2 trials from session 1 and 2 trials from session 2) were averaged to determine the mean jump distance, mean throw distance, and a mean value for the self-selected goal for the week. Two trials from 1 session were averaged for the 1 missed session. The standard deviation (SD) of all 4 trials was calculated to show the variability in performance over the 4 trials within 1 week. The mean and SD were graphed weekly. The graphs were analyzed visually to describe (a) the variability in jumping and throwing distance and performance of a self-selected goal from week to week, (b) the stability (ie, no decline or improvement in mean jump distance over 3 consecutive weeks) of jumping and throwing distance and performance of a self-selected goal, and (c) the trends in performance from week 1 to week 10. The PES ratings were reviewed and described for each participant along with any safety concerns. The BOT2 composite standard scores were described for each participant to demonstrate change from pretest to posttest. The CAPE scores for the physical activity domain were described for each participant. Statistics were not used to analyze data because of the small number of participants.

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The home program model resulted in a very high rate of attendance. Attendance in the exercise sessions was 98% (59/60 sessions). The following terms were used to describe results: (a) maintenance (no change from preceding data point, (b) improvement (positive change from preceding point), and (c) decline (negative change from preceding data point). Stability refers to no decline or improvement over a series of 3 data points, and consistency refers to the ability of the participant to replicate their performance consistently during testing on jump distance, throw distance, and performance of their self-selected goal for the week.

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Primary Outcome Measures
Standing Broad Jump

Participant 1 (10 years old) increased the mean distance she jumped over the 10-week intervention from 128 to 135 cm. The distance increase reflected a change from the 40th percentile in week 1 to the 55th percentile in week 10. The SD did not change from week 1 to week 10. There was a gain in mean jump distance, although no change in the consistency of jump performance from beginning to end. She demonstrated a pattern of maintenance, improvement, decline, and finally improvement. Jumping distance never achieved stability.

The mean distance participant 2 (7 years old) jumped over the 10-week intervention improved slightly from 86.5 to 87.5 cm. She remained in the 32nd percentile at both pretest and posttest. The SD decreased by 7 cm when comparing week 1 with week 10, reflecting improved consistency in jumping distance. Although no gain was seen in the mean jump distance, consistency in jump performance improved. She demonstrated an inconsistent pattern of performance from week to week. First demonstrating maintenance, decline, improvement, maintenance, improvement, decline, followed by improvement. Jumping performance never reached stability.

Participant 3 (5 years old) demonstrated a decrease in the mean distance he jumped over the 10-week intervention from 111 cm in week 2 to 103 cm in week 10. He declined from the 70th percentile in week 1 to the 50th percentile in week 10. The SD decreased 5 cm from week 2 to week 10. Baseline was set at week 2 since he simply stepped forward rather than jumped during week 1. There was not a clear change in jumping distance or consistency over time. He demonstrated a phase of decline, improvement, decline, and finally slight improvement. Jumping distance never reached stability (Figure 1).

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Basketball Throw

Participant 1 increased her mean throwing distance over the 10-week intervention from 445 to 563 cm, reflecting a change from the 10th percentile to the 35th percentile from week 1 to week 10. The SD declined by 24 cm from week 1 to week 10. There were gains in both mean throw distance and consistency in throwing performance from the beginning to the end. She demonstrated a pattern of steady improvement to a plateau during weeks 8 to 10.

Participant 2 increased the distance she threw over the 10-week intervention from 182 to 190 cm, reflecting a change from less than the 10th percentile to the 10th percentile from week 1 to week 10. The SD decreased 17 cm from week 1 to week 10. There were gains in both mean throw distance and consistency in throwing performance from the beginning to the end. She demonstrated a pattern of decline, improvement, decline, and finally improvement. Throwing performance never reached stability.

Participant 3 increased the mean distance he threw over the 10-week intervention from 178 cm in week 2 to 213 cm in week 10. He remained below the 10th percentile from pretest to posttest. The SD decreased 95 cm from week 2 to week 10, reflecting more consistency in throwing distance. Baseline was reported at week 2 since he simply dropped the ball instead of throwing the ball the first week. In light of that, if one considers week 2 as the beginning of cooperation with testing, there is a gradual though nonlinear improvement in throwing distance and consistency through week 10. His demonstrated a pattern of improvement, decline, improvement, decline, and then reached a plateau (Figure 2).

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Self-selected Goal

Participant 1 decreased the mean time for the basketball drill by 13.5 seconds, participant 2 achieved her goal of decreasing the number of step downs with her feet on a bike without pedals by week 5, and participant 3 increased the mean number of jumps with a jump rope slightly (from 0 to 2.5 jumps). All participants had decreased SD values, reflecting more consistent performance. Baseline was reported at week 3 for participant 3 since he was still learning to jump rope during the first 2 weeks (Figure 3).

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The PES, counts of throws and jumps, and ability to perform the exercise with correct technique were used to increase the exercise load. A safety log of concerns regarding complaints about fatigue, muscle soreness, injuries, and falls was kept. At 10 years of age, participant 1 was able to accurately report her perceived exertion and reported scores between 4 and 6 for all sessions. However, the younger participants rated how difficult the exercises were for them to perform or how much they liked the exercise. They rated exertion from 0 to 9, with no consistent pattern in relation to apparent effort. The participants began the intervention at 30 to 40 ground contacts per session. Jumps were gradually increased until participants were performing 120 to 124 ground contacts per session. All 3 children fell, although were not injured when performing the jumping exercises. There were 7, 6, and 6 falls for participants 1, 2, and 3, respectively, over the 10-week intervention (average of 1 fall per 350 jumps). Participant 1 experienced finger pain (no swelling or injury) when catching the weighted ball that resolved with no treatment and complained of fatigue or muscle soreness during 12 sessions. The activities were modified to roll the ball or catch the ball for the participants if it was deemed necessary. The exercise load was not increased if she complained of soreness.

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Secondary Outcome Measures
BOT2 Z Scores, Standard Scores, and Minimum Important Difference Scores

Two of the 3 participants improved on the total motor composite Z score from pretest to posttest (a change of +0.7 and +0.1), reflecting an improvement in motor proficiency in relation to age/sex-matched peers. Participant 3 declined 0.2 SDs, and changes in manual coordination and strength/agility items were responsible for the decline. Participant 1 improved in all standard score composites (a change in fine motor composite = +4, manual coordination = +7, bilateral coordination = +8, strength/agility = +1), and the changes exceeded the MID scores,25 reflecting a clinically important improvement from pretest to posttest. Participant 2 improved in 2 composite scores (a change in bilateral coordination = +5, strength/agility = +5) and the changes exceeded MID scores,25 reflecting a clinically important improvement from pretest to posttest. Participant 3 improved in fine manual control and bilateral coordination (a change of +6 and +5, respectively). He declined in manual coordination and strength agility (a change of −9 and −4, respectively). The changes exceeded the MID scores,25 reflecting a clinically important decline from pretest to posttest (Table 2).

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CAPE: Physical Activity Domain

Participant 1 declined in the average diversity of physical activities by 4 and declined in the average intensity from an average of 2 to 3 times a month to an average of 2 times in the past 4 months from pretest to posttest. Participant 1 also had a 3-point change in the average “with whom” domain, which was the largest change of all the domains for all 3 participants. Participant 2 increased the average diversity of physical activities by 2 and remained at an average intensity of 2 times in the 4 months from pretest to posttest. Participant 3 increased the average diversity of physical activities by 2 and remained at an intensity of 2 times in the 4 months from pretest to posttest. Enjoyment of physical activity increased in participant 1, showed no change in participant 2, and decreased in participant 3 (Table 3).

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Our hypothesis that the plyometric training program would improve jumping distance was supported in 1 participant. Two participants improved in the average distance they could jump (7 and 1 cm), whereas 1 participant declined 8 cm over the 10-week intervention. The changes in jumping distances of participant 1 reflected a percentile change of 15. The improvement in jumping for participant 2 was very small and did not result in changing percentiles from pretest to posttest. This participant had the lowest BOT2 scores, indicating a more severe motor delay. Participant 3's pre- and posttest percentiles were both below the 10th percentile and the magnitude of change could not be determined. Participant 2's lack of change and participant 3's decline in jumping distance may have been age related since only the oldest participant benefited from training. A motor learning approach rather than a resistive exercise approach may be more beneficial for younger children.

All 3 participants improved in throwing distance (118, 3, and 35 cm), reflecting changes of 25% for participant 1 and 10% for participant 2. Participant 3's improvement could not be determined from the percentiles since he was below 10% at pretest and posttest. They also improved in the consistency of throwing distance. Given the trend for motor performance to become more consistent with practice, it is possible that children with NF1 have low coordination reflected in excessive variability and poor execution of a motor task. It appears that consistency of throwing and jumping performance preceded gains in throwing and jumping distance. Gains of 30% have been reported24 in jumping and throwing distances after a 10-week resistive training program for children with typical development. The gains observed in these 3 children were between 0% and 25%. This difference may be attributable to the need for children with motor delays to learn and refine the motor skill before showing changes in throwing distance. Not all participants reached stability in motor performance. A 10-week plyometric training program may not have been long enough to gain optimal effects for children with NF1. Expected outcomes in the 3 participants appeared to be influenced by the severity of motor delay, age, and rate of skill acquisition.

All 3 children improved in their ability to perform their self-selected goal. They achieved their goal with a very limited amount of practice time, 5 to 10 minutes per session. Since this goal was self-selected, motivation and practice outside of therapy may have influenced goal achievement. The PES was useful for monitoring exertion for the 10-year-old participant. However, an alternate means of monitoring exercise intensity may be necessary for children younger than 10 years since the 5- and 7-year-old participants were unable to accurately report perceived exertion. Counting the number of ground contact times was useful to prevent a high number of jumps. Falls were spread out over the intervention and did not appear to be associated with learning new exercises or increasing the intensity of exercises. There were no injuries from falling, and the rate of falling was low for all 3 participants.

We saw improvement in the BOT2 scores in the body coordination composite both in relation to age/sex-matched peers and within the participant from pretest to posttest. Two subjects made gains in the strength/agility composite similar to the results reported in research on children who are developing typically.17,18 The decline in the strength/agility composite for participant 3 is concerning. Individual muscle strength was monitored by hand-held dynamometry, and he did improve. Despite his ability to increase muscular force production, he did not improve his performance on the fitness tests assessing general strength. His performance at the posttest might reflect inattention, behavior, or fatigue during testing.

Two of the 3 participants increased the diversity of physical activity but did not change the intensity of physical activity. Participant 1 declined in both diversity and intensity of physical activity, and her declines may have been attributed to family circumstances (her sister's wedding and father's work travel). However, she had a change of 3 points in the “with whom” category, indicating that she went from being mainly alone to being with friends during her physical activity. This change was attributed to going to the playground and playing with friends rather than family. Dancing, water sports, gardening, team sports, and playing on playground equipment activities accounted for the changes in diversity and appeared to be related to seasonal fluctuations (from fall to winter). Enjoyment improved in 1, remained stable in 1, and declined in 1 participant. Our hypothesis that a plyometric training program would result in increased physical activity participation and enjoyment was not fully supported. Previous research has shown that personal factors (age, sex, and functional ability) along with environmental factors (family preference, income, parental education, and marital status) may limit or facilitate participation in recreation and leisure activities.38 The levels of diversity and intensity of participation for the 3 children with NF1 were similar to those reported by Law et al39 for children with minor motor disorders. Participation in recreational and leisure activities is a complex phenomenon. A physical therapy program that includes interventions to address personal barriers may result in increasing the intensity of recreational and leisure activities. Environmental factors, such as change in season and major family events, help to explain the changes in participation diversity and intensity for these children. Use of repeated CAPE assessments over short durations appeared to be influenced by seasonal variation in activities and family circumstances. In addition, 10 weeks may be too short a time to see changes in scores reflecting family lifestyle modifications.

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A 10-week plyometric training program resulted in improved consistency in throwing and jumping distance in 3 children with NF1, although expected improvement was less than the values reported for children who are developing typically. Improved consistency tended to precede changes in distance. The program resulted in improvement in body coordination for 3 children and in strength/agility for 2 of them. The response of children with NF1 to training may be similar to the response of children with typical development. However, the program duration may need to be longer to achieve optimal outcomes. It is possible that the length of the intervention and the response to the training program may vary depending on the severity of motor delay, the age of the child, and the presence of comorbidities such as learning, behavior, attention, and musculoskeletal impairments.

Because plyometric training includes high-impact and explosive actions, safety precautions and accommodations for the activities should be integrated into training programs. Because the safety of plyometric training has not been rigorously evaluated in young children, therapists should provide adequate supervision, ensure proper technique, use appropriate training loads, and monitor children for signs of injury. A limitation of this case series was the lack of blinded assessments. Larger experimental studies including a control group and blinded assessments will be necessary to account for maturation and to see whether these results can be generalized to other children with NF1.

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The authors thank the 3 children and their families. They also thank Judith Holt, PhD, as an advisor; Amber S. Perry, DPT, Soffe Lowell, Austin Stevens, Katie Smith, and Janice Davis for assistance in carrying out and coordinating the study; and Drs Bruce MacWilliams, David Viskochil, Jacques D'Astous, and John Carey for their advice on protocol, design, and resource management.

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case report; child; exercise therapy; neurofibromatosis type 1; outcomes; plyometric training

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