Cerebral palsy (CP) is a group of debilitating motor disorders resulting from insult to the brain during the first 2 years of life, with nearly 80% of cases occurring within the prenatal period with an etiology never identified (1). With an incidence of approximately 2.5 per 1000 live births in the United States, CP remains the most common physical disability among children (2). CP carries a wide array of clinical presentations ranging from isolated physical or cognitive impairment to global loss of function.
Several classification systems have been used to categorize these patients into groups for management protocols and epidemiological purposes; however, the Gross Motor Classification System (GMCS) is the most useful from a movement and exercise standpoint. The GMCS assigns classification grades I to V to patients based on severity of physical impairment as follows:
- Class I — Ability to ambulate
- Class II — Independently ambulates with limitations
- Class III — Ambulates with walking aids
- Class IV — Independently mobilizes with powered mobility
- Class V — Dependent on assisted devices for all mobility (3).
Challenges Faced by Patients with CP
Within the last 10 years, advancements in medical technology have enabled better understanding of the underlying etiology of CP and have broadened our knowledge of the associated pathophysiology. This in turn has assisted the development of comprehensive and evidence-based treatment plans for this diverse population. Effective treatment of children with CP requires a multidisciplinary approach with several health care professionals including physicians of varying specialties, therapists, nutritionists, and skilled nursing staff. Management should be tailored to each patient and focus on the capacity of the individual. Various recommendations and guidelines for exercise and physical activity have been produced to reduce morbidity and mortality in this population. Several epidemiological studies have demonstrated that individuals with CP who have higher GMCS classifications along with accompanying sedentary lifestyle, have a risk of developing cardiovascular disease with an increased incidence of hypertension, hyperlipidemia, type 2 diabetes, and central obesity. Additionally, CP patients suffer from degenerative joint disease, osteoporosis, osteoarthritis, hip displacement, and chronic joint pain as a sequelae of their condition (4–9). This sedentary lifestyle also makes them prone to overuse injuries and muscle soreness when first starting a new exercise routine.
Current exercise and physical activity regimens and recommendations for CP patients
The American College of Sports Medicine (ACSM) recommends healthy adults participate in 150 min of moderate-intensity cardiorespiratory exercise and muscle strengthening at least 2 d·wk−1 (10). These guidelines have been shown to improve stamina and functional capacity; decrease the incidence of obesity; reduce the development of osteoporosis and fracture incidence; reduce the incidence of type 2 diabetes by decreasing insulin resistance; and reduce cardiovascular complications, including coronary artery disease, hypertension, and cerebrovascular accidents (11). While there are no consensus statements that provide standardized recommendations for adults with CP, the majority of the studies reviewed revealed that this population can benefit from even a reduced dose of exercise and physical therapy.
In their reviews, Tudor-Locke et al. (12) and Verschuren et al. (13) demonstrate that CP patients gain similar benefits from exercise and physical therapy in accordance with ACSM. Furthermore, the studies also demonstrate that CP patients still experience benefits even with reduced frequency and intensity.
Baseline Physical Activity in Individuals with CP
Current recommendations suggest that increasing physical activity in individuals with CP beginning in childhood and continuing through the critical periods of adolescence is key to improving morbidity and mortality rates within this population. Carlon et al. (14) showed that school-age children with CP are 30% less engaged in physical activity than their healthy counterparts and two times more likely to be engaged in sedentary behavior. It also has been found that more than 75% of children and adults with CP spend nearly all of their waking hours engaged in sedentary activities (13). Baseline activity represents tasks performed by healthy individuals on a daily basis, such as housework/cleaning (3.3 metabolic equivalent of task [MET]), sitting (1.2 MET), standing (1.3 MET), and slow/average speed walking (3.0 MET) (15). Within the CP population, only GMCS I to III patients are able to reach this, because patients with GMCS IV to V are unable to perform activities greater than 1.0 MET.
All individuals can benefit from a baseline assessment of physical activity when preparing to start an exercise program. Individuals with CP in particular can benefit by creating individualized programs that are designed to reduce injury, provide adequate recovery time, and monitor engagement for continued interest. The majority of CP patients are moderately to severely deconditioned and are prone to injury, excessive muscle tenderness, fatigue, and diminished improvement in exercise capacity. Health care professionals should become familiar with signs and symptoms of overtraining to adjust the regimen to maximize the benefit for the individual and reduce morbidity (16).
Therapeutic goals of CP patients differ based on their GMCS classification. Classes IV to V have significant motor limitations and will struggle performing structured exercise programs. Mild physical activity, such as range of motion exercises and stretching, should be recommended for this subtype as it reduces their amount of sedentary activity (17). In general, individuals with CP should not exceed 2 h·d−1 engaging in nonoccupational leisure activities and should be encouraged to break up prolonged sedentary activities with 2 min of active movement every 30 to 60 min (16).
Cardiorespiratory endurance training in patients with CP
Aerobic exercise has been a study focus for CP patients because of their sedentary lifestyle and the strong correlation of cardiovascular fitness with improved health. Randomized controlled trials (RCTs) performed on individuals with CP have demonstrated a significant increase in aerobic endurance, although typically only noted in GMCS I to III. Trials were evaluated in sessions per week, intensity of action, duration, and type of exercise (18).
The protocol from the studies reviewed included two to four sessions of training every week for the duration of the individual trials. These deviated from the ACSM recommendations of three to five sessions per week in an effort to assess the benefit of decreased exercise frequency. Further consideration of baseline activity, functionality, and level of deconditioning was included in the exercise prescription, making sure to afford sufficient time for healing to prevent regression of endurance gains. The experimental groups demonstrated a significant increase in aerobic endurance, suggesting that even individuals with lower levels of conditioning can receive benefits with very few sessions and with gradual increases in endurance (13,18).
In their comprehensive review, Verschuren et al. (13) evaluated the intensity of the training and found that even though the intensity, graduation of intensity, and duration varied among participants, all studies demonstrated that individuals with CP were able to attain similar cardiorespiratory benefits as their healthy counterparts.
Based on the comprehensive review, Verschuren et al. (13) recommend prescribing cardiorespiratory activities to CP patients at a frequency of two to three times per week, with an effort of 40% to 80% of heart rate reserve or 50% to 60% of peak oxygen consumption at a minimum of 20 min, for a duration of 8 wk to measure increases in endurance and other health benefits. Unfortunately, adherence to exercise programs is challenging with most patients abandoning a new regimen within 7 d. This is even more challenging in GMCS III to V in which a successful exercise program is dependent on the commitment of both patient and the caregiver.
A study in 2007 demonstrated that many individuals lost much of the cardiorespiratory endurance and mobility benefits within 4 months of discontinuing routine exercise. Thus, it is important to maintain regular activity to receive the sustained benefits, because short courses of increased aerobic activity provide no sustained permanent benefit once activity is diminished (19).
Peak oxygen uptake (V̇O2peak) typically is used as a measure of aerobic fitness, and this is generally lower in children with CP as has been shown through exercise tests using cycle ergometry or a treadmill (20,21). Timed walking tests, such as the 6-min walk test (6MWT), has been shown to predict cardiorespiratory fitness in both healthy and severely disabled children, whether or not used with gas collection (21,22). In a case study, six children participated, four of which had bilateral or unilateral spastic CP levels I and II based on GMCS, and two normally developed children. According to Jung et al. (23), the age of the participants was 5 to 16 years, and the ability to walk continuously for 6 min and have the ability to provide informed consent were inclusion criteria. Patients had their concentration and volume of oxygen (V̇O2), peak respiratory exchange ratio, and minute ventilation measured simultaneously by preVent pneumotachs. This limited study revealed that children with CP have lower V̇O2 peak values, as well as shorter walking distances in set times than normal children. This, therefore, suggests that children with CP tend to participate in lower-intensity physical activities. This leads to a cycle of deconditioning causing further deterioration and reduction in activity at young ages increasing the risk of chronic conditions as CP patients age (19).
Resistance and strength training
Similar to cardiorespiratory activity, the long-term health benefits of resistance and strength training have been well documented (24). To achieve these benefits, the National Strength and Conditioning Association (NSCA) recommends following activity guidelines based on current activity level for healthy individuals:
- (1) youth/beginners, perform 1 to 2 sets for 10 to 15 repetitions without significant muscle fatigue;
- (2) moderate level athlete: perform 2 to 4 sets with 6 to 12 repetitions prior to muscle fatigue.
Until recently, these benefits were not addressed in individuals with CP and there were no clear consensus recommendations for these patients until Verschuren et al. published in their 2016 review guidelines for resistance training in CP patients (13). It was suggested 2 to 4 sessions per week on nonconsecutive days, performing 1 to 3 sets of resistance exercises at 6 to 15 repetitions or 50% to 85% of 1 repetition max — this pertains to both upper and lower extremities. This helps build muscle strength and mass, which has been proven to decrease the cardiometabolic risk profile, mortality rates, incidents of cardio/cerebrovascular disease, and risk of functional decline with average age. Until recently, strength training was contraindicated for CP patients, especially within the most predominant type — spastic CP, which typically includes patients with GMCS IV to V. The predominantly held belief was that muscle breakdown and fatigue promoted muscle stiffness, which further exacerbated spasticity. However, more recent studies have rejected this notion showing strong evidence that spasticity can be improved with strength training and is relatively safe with few, if any, adverse effects.
It is well known that individuals with CP experience activity and participation limitations. These are often related to impaired walking capacity as it pertains to achieving a certain pace or walking/running a certain distance. Of concern, particularly in children with CP, is that they only have about 36% to 82% of the muscle strength of typical developing children (25). Several methods have been used to increase muscle strength and improve the walking capacity of children with CP. The most commonly used method is progressive resistance exercise training (PRE) (26). Van Vulpen et al. (27) developed a functional power-training program consisting of resistance training with exercise at high movement velocity, using a double baseline-controlled trial, to measure the improvement of both muscle strength and walking capacity. This program demonstrated improved lower-limb strength (13% to 83%), as well as increased walking capacity (18% to 128%), in young children with CP. This study compared the changes in outcome measures after a 14-wk period of usual care with changes after a 14-wk training intervention (functional power training) that was followed immediately by another usual care period. The treatment goals were measured by using a goal attainment scaling. Goals were set which included improvement in running, improvement in walking, and improvement in gross motor activities. According to van Vulpen et al., after functional power training, 86% of children achieved or exceeded their goals; whereas after a usual care period, only 14% of children achieved their goals. The degree to which goals were achieved during the usual care period and during the functional power training period differed significantly (P < 0.001). The degree to which goals were achieved during the functional power training period and during the follow-up also differed significantly (P = 0.006).
Lower Extremity Strengthening
One issue that was consistent throughout the majority of reviewed studies was the lack of inclusion of CP patients with a GMCS IV and V. Five RCTs included CP patients with ages ranging from childhood to adulthood. In all of the studies, participants were required to engage in strength training activities three times a week with the exception of one study that reported only two times per week (13,18).
Only three studies reported in the previously mentioned review article adhered to the NSCA’s recommended level of activity as detailed earlier. In addition to varying levels of activity, multiple studies also varied in duration of strength training activity. Studies ranged from 5 to 8 wk (28–30), and others were 12 to 20 wk in duration, making it difficult to recommend altering guidelines given the large variation in study duration. The previously mentioned review article investigated multi-joint functional exercises to target the recruitment of multiple muscle groups to compile data for their recommended levels of activity. The final recommendations from these studies are as follows for patients with CP: frequency of two to four sessions a week, tailored to individual fitness level; effort of 1 to 3 sets of 6 to 15 repetitions per exercise with effort range of 50% to 85% of one repetition max; and duration of the program should be at least 12 wk to obtain maximum benefit. It is suggested that these recommendations could be applied to individuals with higher GMCS levels as a vast majority of these studies did not incorporate GMCS levels greater than III; however, currently, there are not any studies to support this claim (13).
Another issue that was highlighted in this review is that recent literature has focused largely on the benefits of strength training programs rather than suggestions for creating a universal guideline for these programs with regards to CP patients. One case control study followed 40 children aged 6 to 8 years with GMCS I-II over 6 wk while engaging in a weighted lower extremity strengthening program. This was recorded via preassessments/postassessments with Grade Motor Function Measure dimensions D (standing) and dimension E (walking, running, jumping). The patients demonstrated improved gross motor strength and function when compared with the control group. While this suggests that for GMCS grades I to II, a 6-wk program may prove beneficial to gross motor function (GMF) and strength, the long-term benefits were not addressed (31).
A smaller, but promising, randomized control trial published in 2017 followed 15 subjects aged 6 to 15 years with spastic CP GMCS grades I to III as they engaged in a combined aerobic and resistance training program for 8 wk. This study fell within suggested NSCA guidelines and evaluation criteria and includes common function tests including the 6-min walk test, 10-min walk testing, 30 s sit-to-stand test, and function reach tests for all participants with a pretest and posttest. The results showed significant improvement in lower extremity strength, gait, and balance (32). However, because of the duration of only 8 wk, this study's ability to be used for long-term benefits as an outcome measure is limited. Additionally, the study had low power making its findings weak. Yet, given the methodology and following within the suggested NSCA guidelines, there is an opportunity to expand on this with a larger and more robust trial for future guideline evaluation and long-term benefits.
Another promising study on the horizon is the Strength Training for Adolescents with CP (STAR) trial. This trial is a multicenter RCT developed to evaluate the effects of strength and resistance therapy on gait efficiency. The individuals involved in this study fall within the GMCS grades I to III. The study protocol acknowledges the decline in ambulatory function and increased gait inefficiency between the ages of 20 and 40 years as a particular motivating factor for the need for this type of research and evaluation of long-term benefits of these therapies. This reduction in gait efficiency leads to high-energy expenditure when compared with healthy patients (33,34). Continued decline leads to reduction in GMF and diminished participation and interest in physical activities. This can lead to a worsening spiral that can negatively result in these individuals becoming unmotivated and unwilling to participate in strength and resistance training exercises, which could benefit them.
Gait assessments within CP patients have demonstrated that peak inefficiencies in GMF can begin at 12 years of age. These functional inefficiencies lead to progressive GMF decline, which can lead into the cycle as mentioned above. The STAR study aims to target individuals within this narrow spectrum to halt this negative cycle and improve outcomes. One of the proposed mechanisms for gait improvement in these patients is incorporation of targeted resistance training via reduction of co-contraction of antagonistic muscle groups leading to spasticity. The hypothesis of the study is that resistance training focused on ankle plantar flexors will improve efficiency of gait through neural and biochemical adaptations leading to lasting improvements. The study plans to include 60 participants within the RCT to determine evidence-based benefits of strength training in CP patients (34). Unfortunately, no follow-up data have been published to date; however, the design and focus on long-term outcomes can be a model for future studies to assist in developing and finalizing guidelines for lower extremity strength and resistance training in CP patients.
Upper limb impairment is estimated to occur in 50% to 70% of patients diagnosed with CP and is most commonly observed in patients with hemiplegia, though this can occur in other CP subtypes, such as monoplegia and quadriplegia (1,2). CP patients with upper limb impairment often experience muscle weakness, spasticity, decreased motor function, and an impaired sensory mechanism. These symptoms often limit motor performance and participation in daily activities and frequently lead to limb preference with resultant further decline in function of the least functioning limb (35). This negative cycle is an area of focus for strength and resistance training in patients with CP to prevent limb preference and worsening motor function.
Current therapies that target the upper limbs include constraint-induced movement therapy (CIT), hand-arm bimanual training (HABIT), and strengthening exercises for spastic muscles. Approaches to gross motor rehabilitation in both unilateral and bilateral studies have shown improvement in upper limb function; however, patient adherence to intensive training programs has been found to be difficult to establish and maintain (36–38). This difficulty with long-term commitment has limitations on the strength and resistance activities in both the intensity and duration that is required to potentiate long-term improvement in CP patients (37). Despite the challenge of patient compliance and adherence, the development of new technologies has provided clinicians the ability to develop therapeutic services that patients are adherent to and afford providing clinicians the ability to monitor patient progress remotely. One of these new innovations in therapies is the home-based rehabilitation programs facilitated by digital communication technologies. This new method of therapy has improved both patient satisfaction and compliance and further encouraging the improvement of current and new rehabilitative approaches in the development of guidelines for patients with CP (37).
CIT and HABIT have been regarded as both safe and the most successful therapies for improved motor performance in patients with unilateral CP (36,39,40). However, despite the success of both programs, CIT and HABIT are regarded as intrusive and impractical by clinicians, patients, and caregivers because of the intense protocol. Recommendations include intensive training splits of up to 6 h·d−1 for 5 d·wk−1, with a cumulative total of 60 to 90 h of training (36,37). While recent studies support older findings of improved functional status with this training methodology, there was no significant correlation between intensity and length of constraint on functional status for patients undergoing CIT. There also was no noted significant correlation between intensity and scheduling regarding functional status for patients undergoing HABIT (36,41). This is in direct contrast with a 2008 study by Gordon et al. (42) that found, for both CIT and HABIT, 90 h of intensive training was significantly more effective for improving functional status in CP patients than 60 h of intensive training. This highlights the need for further studies on patient outcomes following intensive treatments and the duration required. With conflicting data, it is imperative that an area of interest for future research in this field be focused on duration for optimal outcomes following strength and resistance training in CP patients.
In addition to the burden of maintaining rigid training schedules, the intensive protocols have been reported to have adverse effects on children with CP leading to frustration, inattention, and a lack of motivation (36,37). These adverse effects can not only lead to negative consequences in other areas of life but also can directly correlate with compliance and adherence to strength and resistance training activities in the future. In light of these concerns, recent studies have aimed to maximize the positive benefits of CIT, while minimizing the negative impact on patients and caregivers.
One of the modified protocols for CIT is the home-based Friendly-CIT, or Gentle-CIT. Researchers introduced three adjustments to the current protocol by improving schedule, adding gentle restraint of the unaffected arm, and providing a playful environment, all while allowing the child to remain in their home for therapy. Fifteen children with CP were chosen to participate in a preintervention and postintervention trial for 8 wk of 36 h of Friendly-CIT. Motor and psychosocial outcomes were evaluated both pretherapy and posttherapy. Following therapy, there was significant improvement in motor function, as well as an increase in playfulness. In addition, caregiver stress remained stable over the 8-wk study without an increase throughout the therapy. This approach has shown promise, although further studies are necessary to determine the long-term impact of this approach as a viable option for upper extremity therapy for patients with CP (38).
Preliminary studies for a modified version of HABIT, Home-Hand Arm Bimanual Intensity Training (H-HABIT) showed improved bimanual function in seven children with unilateral CP aged 29 to 54 months. H-HABIT was provided by trained caregivers for 2 h·d−1, 5 d·wk−1, for 9 d. Bimanual tasks were accessed via camera before and after therapy. All seven children included in the study experienced improved temporal and functional bimanual movement following the 9-d H-HABIT intervention (43). They did not have any long-term follow-up to comment on sustained benefit of their intervention. However, this suggests that future studies can test similar modified trials for both upper-extremity strength, as well as other components, such as caregiver stress and compliance versus the standard HABIT.
Several studies have demonstrated that intensive therapies, such as CIT and HABIT, improve upper body function in children with CP, but there is not any substantial research on the effects of power training on the upper extremities. Traditional resistance training for CP patients incorporates the use of weights, resistance machines, medicine balls, and resistance bands, which have been found to improve expiration and grip strength in children with CP. However, these training modalities are not useful for measuring power output via incorporating force and velocity (13,35,44).
A recent study assessed a home and community-based approach for upper extremity power training using The Concept2 SkiErg, a device designed to provide feedback on power output as a cost-effective way to monitor patient progress. Youths diagnosed with CP, ages 7 to 24 years, were chosen to participate in a 6-wk study. This study involved training that took place three times a week in either the participant's home or school. Preliminary findings suggest that community-based upper extremity power training increased power output in youth with CP, and several participants noted a decrease in pain after the 6-wk training period — indicating a need for further studies on power training for individuals with CP (35). Anecdotally, Internet viral sensation Miles Taylor, is an athlete with CP who is known for his ability to deadlift more than twice his body weight, as well as his exuberant celebrations. This suggests that power training of the upper extremities in patients with CP has potential benefits of decreased pain, as well as improved quality of life.
In addition to the home-based models for current therapeutic approaches, researchers have developed new rehabilitative modalities for patients with CP. Action observation therapy (AOT) is a new therapy based on “mirror mechanisms,” which suggests that imitation drives motor controls. Children ages 5 to 10 years with unilateral CP were chosen to participate in 20 sessions of AOT. Participants were tasked to observe and imitate a peer performing dexterity-intensive magic tricks. After 20 sessions of AOT, there was a significant improvement in motor dexterity and hand motor skills of participants when compared with their peers. In addition, children appeared to experience greater improvement if the leading peer had greater motor skill. This preliminary study suggests AOT is a helpful tool for hand rehabilitee programs, either alone or as a combined therapy, for children with unilateral CP (6).
In recent years, innovative research has incorporated the use of gaming technology in current rehabilitation programs. Borstad et al. (45) found that home-based CI therapy delivered through virtual reality gaming to be a safe, enjoyable, and effective therapy for patients with hemiparesis. Other studies have introduced low-cost video gaming devices in resistance therapy to improve upper limb function in patients with CP with promising results (46,47). Several studies have found that home-based resistance training using the Nintendo Wii resulted in an improvement in grip strength as well as improved compliance and motivation in children ages 7 to 12 years with spastic hemiplegic CP (46–48). Similar improvements of upper limb function and satisfaction were observed, in children ages 7 to 16 years with CP, when introduced to video game components adapted for resistance therapy (49). Current research supports the delivery of rehabilitative therapy via gaming technology as a unique and novel approach to improve upper limb function, reduce cost, and improve compliance and satisfaction in CP patients.
The last 20 years have provided a large body of evidence that shows increased health benefits with exercise of both upper and lower extremities for patients with CP (13). However, even the most successful exercise and rehabilitation programs have faced challenges with patient compliance and adherence to protocol — usually because of duration and difficulty. However, these challenges can represent opportunities for future projects to specifically target and improve upon. While upcoming research is encouraging, there are limitations to these studies, including power, standardized measures/outcomes, and inclusion of all classifications of GMCS patients. Future projects demonstrating appropriate activity and benefits in GMCS IV and V will be vital to the advancement of research in this population as these patients are the most severe and will need to be accounted for to prevent even further worsening of their motor function. A standardized method of measurement and outcomes that can be universally applied across various trials would better assist researchers in providing more compelling arguments and recommendations in this field of study. At its current rate of growth, the future appears bright for the development and utilization of new technologies and innovations for strength and resistance training of patients with CP.
There are many different organizations in the United States that promote fitness, exercise, and recreation for people with disabilities. Becoming familiar with some of these and what they offer would be vital to patients with CP. I will briefly mention a few here but I encourage readers to visit the American Academy for Cerebral Palsy and Developmental Medicine web site for more in-depth information. The Northeast Disabled Athletic Association is a nonprofit charitable organization that provides recreational and competitive athletic opportunities for people with physical disabilities. They also support disabled athletes in their pursuit of excellence off the field of play. The National Sports Center for the Disabled is a therapeutic recreation organization providing leadership and expertise in adaptive sports. Disabled Sports USA provides opportunities for individuals with disabilities to develop independence, confidence, and improved fitness through participation in community sports, recreation, and educational programs. The National Center on Health, Physical Activity, and Disability is a public health practice and resource center that offers directories of programs, organizations, and equipment by state, for persons with disabilities. The United States Adaptive Recreation Center works with schools, hospitals, rehabilitation centers, and parks and recreation departments to serve children and adults with all types of cognitive or physical disabilities.
CP is a common neurological disorder and can lead to lifelong functional impairment, as well as an increase in cardiovascular risk factors by way of a sedentary lifestyle. In the last two decades, tremendous strides have been made to improve these patients' outcomes through exercise and physical activity. The ACSM provides guidelines for exercise, and there is no evidence to suggest that these requirements should be any different for those with CP. The caveat is that many people with CP have more physical limitations; therefore, these recommendations may be difficult to achieve. Depending on the severity of CP, some exercises may not even be possible. However, many health benefits may still be achieved by doing less than the recommendations. Being more fit and exercising should not be considered all-or-nothing. Recent literature trends are suggesting that, despite varying modalities and durations, strength and resistance training has been proven beneficial for both upper and lower extremity training in patients with CP (50–53). There is a large need for further research to assess what long term benefits are achieved. This suggests that any increase in activity is better than none, and these patients should be encouraged to continue with exercise, even if only for a few minutes a day. As larger and more robust research studies include both long-term benefits and easily replicable methods, the hope of developing CP-specific guidelines for resistance and strength training will be realized.
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