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Exercise and Musculoskeletal Rehabilitation

Restoring Optimal Form and Function

Walter R. Frontera, MD, PhD

Exercise Physiology Series Editor:
Howard G. Knuttgen, PhD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 31 - NO. 12 - DECEMBER 2021


In Brief: A comprehensive rehabilitation plan for musculoskeletal sports injuries is composed of the acute, recovery, and functional (return to training and competition) phases. Exercise, in its various forms, is an integral part of all three phases. Aware clinicians can tailor exercise and other interventions, such as medications, physical modalities, psychological support, and orthoses, to promote the return of preinjury function for active patients.

Musculoskeletal sports injuries may result in the partial or complete loss of anatomic form and physiologic function. Impairments may occur directly as the result of the injury or indirectly from inflammation, secondary tissue damage, or therapeutic rest or immobilization. Other clinical situations, such as surgical procedures (eg, reconstruction of the anterior cruciate ligament of the knee or the lateral ligamentous complex of the ankle) may cause the same set of conditions. Rehabilitation restores optimal form and function after injury or surgery. In most instances, rehabilitation begins immediately after injury or surgery to minimize the deleterious effects of inactivity and speed the return to training and competition. In some situations, it may start before elective surgical procedures and continue after surgery.

Rehabilitation uses medications (particularly nonsteroidal anti-inflammatory drugs [NSAIDs] and other analgesics), physical modalities (eg, cryotherapy, ultrasound, hydrotherapy), therapeutic exercise (flexibility, aerobic, and strengthening), assistive devices such as orthoses, and interventions to address the psychological and mental health needs of those who have sports-related injuries. For this brief review of basic concepts, the rehabilitation process will be divided into three distinct, but overlapping, phases: acute, recovery, and functional (table 1). Although many rehabilitative interventions will be mentioned, special emphasis will be placed on different types of rehabilitative exercise in all phases.

TABLE 1. Phases of Rehabilitation

PhaseGeneral Goals

AcuteProtect injured tissue from further damage
Control inflammation
Manage pain
Minimize physiologic and functional losses

RecoveryRestore physiologic capabilities, such as flexibility, muscle
strength and endurance, and cardiovascular endurance

Functional   Return to sports-specific training or regular activities
Evaluate equipment requirements (sports equipment and
  orthotic devices)
Prevent reinjury

Acute Phase

Sports medicine clinicians see injured patients who have a combination of symptoms and signs, including pain, swelling, weakness, muscle or cardiovascular fatigue, limited range of motion, joint locking or other mechanical symptoms (eg, joint instability), and decreased sports performance. Symptom duration may be short, as in acute traumatic injuries, or longer, as in chronic overuse injuries. Rehabilitative interventions, including various types of exercise programs, are designed to address these impairments and the resulting functional losses.

In the acute phase of a traumatic musculoskeletal injury, pain and swelling require immediate attention. Functional rehabilitation cannot be started until analgesia is effective and inflammation is controlled. Patients with chronic overuse injuries may also report acute pain and show signs of inflammation, especially when they train and compete. Physical modalities, such as cryotherapy, and pain medications may help control the symptoms, limit secondary tissue damage, and facilitate the use of exercise for treatment.

Alternative interventions for pain control, such as transcutaneous electrical nerve stimulation and acupuncture, should also be considered. The protection of injured areas and surrounding healthy tissue from additional damage is being studied, and more investigations are needed in this area. Minimizing tissue damage has obvious implications for rehabilitation. If the extent of the physiologic deficit is lessened, more aggressive interventions can be started earlier in recovery.

Static muscle actions. Pain and swelling limit the injured patient's ability to exercise and participate in sports. This is partly a voluntary decision by the patient, who may anticipate discomfort, and partly a muscle-reflex inhibition.1 When pain and inflammation are under control, it is reasonable to begin rehabilitation. Beginning with static (ie, isometric) muscle actions helps to maintain muscle strength and mass, and this approach is well-tolerated by patients, because it avoids joint movement. Static muscle training must involve maximal voluntary efforts at a comfortable joint angle, last for 5 to 10 seconds per repetition, and be repeated several times a day. With static training, adaptations in muscle strength will occur mainly at the joint angle at which the exercise was performed.2 Thus, for adaptations to occur throughout the range of motion, static exercises must be done at multiple angles. When the patient is ready, dynamic exercises to move the joints are implemented.

Joint activation. If the patient is comfortable, active joint exercise with no load or with minimal external load can be performed through pain-free range of motion. Sports-related injuries rarely require prolonged bed rest, but progressive resistance exercise during bed rest can prevent, at least partially, the reduction in strength and muscle mass associated with inactivity.

The recruitment of motor units may be maximized by superimposing electrical stimulation during voluntary static muscle actions. Electrical stimulation may reduce pain and help overcome some of the reflex inhibition associated with joint swelling. Thus, electrical stimulation and voluntary muscle activation may have a synergistic effect during immobilization after injury or surgery.3 Frequently, high-voltage pulsed (alternating) galvanic stimulation is used to enhance tissue healing, provide analgesia, and activate muscle directly. This technique is more comfortable for patients than is direct galvanic stimulation.

Recovery Phase

Controlling pain and inflammation may take several days. During this time, pain medication may be continued. Physical modalities, such as superficial heat (eg, hydrocollator packs, hydrotherapy, paraffin), deep heat (eg, microwave, ultrasound), or electricity, may alleviate pain, reduce edema, increase circulation to the injured tissues, enhance tissue healing, and improve collagen flexibility. For example, ultrasound has been shown to enhance the tensile strength of healing tendons.4 Cryotherapy may continue to be useful, particularly after exercise training sessions. Because of the effect on tissue extensibility, deep heat modalities may facilitate the recovery of joint range of motion and flexibility, especially when the stretching is done during ultrasound application.

Sometimes bed rest or immobilization is necessary in the acute phase, and, when added to the initial tissue damage and inflammatory response, it may have dramatic physiologic consequences. Loss of flexibility or joint range of motion, skeletal muscle weakness, reduced muscle endurance, and diminished cardiovascular endurance or aerobic capacity are concerns. The biologic events that underlie these impairments are activated hours after the tissue insult or the implementation of therapeutic immobilization. Substantial physiologic losses can result in a matter of days. For example, muscle protein catabolism leading to atrophy can be seen 6 hours after joint immobilization in animal models. Thus, the sooner patients can make the transition from the acute phase to the recovery phase, the better. However, symptom relief does not mean that physiologic losses and functional capacity have been restored. In the absence of proper rehabilitation, a premature return to training or competition may be associated with reduced performance and a higher risk of reinjury.

Flexibility During Recovery

Although several types of exercise can be initiated simultaneously early in rehabilitation (table 2), recovery of joint range of motion should receive priority. Many rehabilitative interventions cannot be fully useful unless normal joint flexibility is restored. Full range of motion will allow dynamic exercise training and functional activities that simulate sports-specific actions. Flexibility training can be accomplished with a number of stretching routines, including static techniques and proprioceptive neuromuscular facilitation (PNF) techniques, such as the contract-relax and the contract-relax-antagonist-contract methods.5 PNF techniques may be more effective but are more complex and may require a knowledgeable assistant. Stretching exercises should be performed after—not instead of—a warm-up, because it is easier to stretch the soft tissues when they are warm. Also, the combination of active warm-up and stretching is more effective in increasing joint range of motion than either technique used alone.

TABLE 2. General Recommendations for Exercise During the Recovery Phase

GoalExamplesFrequencyDurationIntensity

FlexibilityStatic stretches

PNF
Daily, 2-3 sets

Daily, 2-3 sets
3 reps of
30-60 sec/set
3 reps of
10 sec/set
Pulling sensation
but not pain
Pulling sensation
but not pain
Muscle
strength
Limb weight,
free weights,
weight machines
3-4 times/wk8-12 reps/set,
3-5 sets for each
muscle group
60%-80% of 1 RM
Muscle
endurance
Limb weight,
free weights,
weight machines
3-4 times/wk> 20 reps/set,
3-5 sets
30%-50% of 1 RM
Aerobic powerBicycling,
swimming,
rowing
3-5 times/wk20-60 min40%-85% of
maximum heart rate
reserve

PNF = proprioceptive neuromuscular facilitation; 1 RM = one repetition maximum

The standard recommendation is that stretching exercises be done two to three times per day. This is based on the observation that, following a stretching session, the newly achieved maximal joint range of motion can be retained for approximately 4 to 6 hours. As with any type of exercise, the duration and number of repetitions to be performed must be accurately defined in each training session. Taken together, scientific studies suggest that static stretching techniques require three repetitions of approximately 30 to 60 seconds each for every joint or muscle group in each training session.6 In contrast, proprioceptive neuromuscular facilitation techniques may require three stretches for 10 seconds each per training session.6

Recovering Strength

Muscle weakness is a common finding in patients who have acute or chronic injuries.7 One explanation is that initial treatment effectively alleviated the symptoms, but the rehabilitation was not comprehensive enough to restore full function. Another explanation is that the duration of rehabilitation may have been insufficient to induce substantial and permanent physiologic adaptations. Years after an injury, patients can have significant strength deficits, even when the injury may have occurred distal to the muscle group being tested (eg, weakness of the knee extensors in athletes who have history of ankle sprains or fractures). Significant muscle weakness of the uninjured contralateral side has also been reported.8 Thus, an important goal in the recovery phase is to restore strength to at least preinjury levels in the muscle groups proximal and distal to the injured area. The implementation and completion of a strength conditioning program is the best way to accomplished this.

Dynamic exercises. As soon as the patient is comfortable within a range of motion, exercises to increase strength may commence. Initially, the exercises can be limited to pain-free range of motion, or to the postoperative range of motion allowed by the surgeon. Progression of range-of-motion exercises should follow increases in flexibility as discussed above. Strengthening exercises should include concentric and eccentric muscle actions, because both are needed in many functional and sports activities. Exercises that include both actions enhance the strength gains associated with strength conditioning programs better than concentric alone.9 Obviously, adding eccentric actions must be done gradually and monitored closely because of the potential to induce muscle soreness.

Exercise prescription. In general, strength rehabilitation programs can be administered three to four times per week. Although recommendations vary, training sessions usually consist of three to five sets of 8 to12 repetitions at the prescribed intensity. Rest periods between sets are usually 2 to 4 minutes but can be shortened as the patient improves and increased intensity is desired. The optimal intensity range can be expressed in relation to the repetition maximum (the maximal load that can be lifted throughout the full range of motion for a given number of repetitions without fatigue). Based on the one repetition maximum (1 RM) concept (the maximal load that can be lifted throughout the full range of motion once but not twice), the optimal intensity range for training in the recovery phase is 60% to 80% of 1 RM. The intensity can be determined using other methods described by Kraemer (see "Strength Training Basics: Designing Workouts to Meet Patients' Goals"). Generally, during the recovery phase, the relative intensity of the training should be maintained and the load increased as the patient gains strength (thus the name "progressive resistance exercise"). Other approaches to strength conditioning have been studied, but some techniques (eg, periodization) may be more appropriate for the functional phase of rehabilitation and sports-specific conditioning than for the recovery phase.

Training variables. Strength conditioning recommendations for the injured patient include many important elements, such as the selection of muscle groups, sequence of exercises, duration of rest periods, and the combination of various routines.10 The type of resistance used can be the weight of the patient's limb (eg, straight leg raises), free weights (eg, dumbbells), dynamic exercise equipment (eg, pulley systems, leg extension bench), or isokinetic devices. Weight machines may be safer, be less difficult to master, and facilitate the isolation of muscle groups for training purposes. Isokinetic devices are very popular, but no scientific data show the superiority of isokinetic programs.

Both open-kinetic chain (free distal end of the exercising segment) and closed-kinetic chain (distal segment is in contact with a surface) exercises can be effective, depending on the injury and the rehabilitation goal. Muscle groups may be isolated during open-kinetic chain exercises, and more co-contraction of various muscle groups occurs during closed-kinetic chain exercises. Some authors11 have reported that the strain on the anterior cruciate ligament is lower during closed kinetic chain exercises, but this is not a universal finding.

Restoring Endurance

Muscle weakness and fatigue are common after a period of inactivity. During recovery, the goal is to rebuild muscle strength and general aerobic conditioning to near preinjury levels.

Local muscle endurance. A reduction in muscle endurance can be caused by the effects of the injury and deconditioning on elements of the oxygen transport chain, such as capillary supply to the muscle and mitochondrial function.12

Training to regain local muscle endurance is based on a high number of repetitions (usually > 20) per set with light loads and relatively short rest periods (1 to 2 minutes) between sets. In contrast, standard strength conditioning uses fewer repetitions with high loads. It is usually best to begin local muscle endurance training after general strength conditioning has been implemented.

Aerobic power. The effects of deconditioning and rest—the frequent companions of injury—on maximal aerobic power and endurance are well known.13 An injury interrupts sports training and may require varying degrees of inactivity that result in detraining. Maximal aerobic power and the ability to sustain a given level of oxygen uptake for a prolonged period of time are diminished.

During the recovery phase of rehabilitation, particularly in the presence of pain, swelling, and limited joint range of motion in the lower limbs, the best endurance conditioning programs limit weight bearing. Activities such as swimming, cycling, and rowing are ideal to prevent or minimize detraining. An arm ergometer can also be used to maintain aerobic conditioning when the injury affects the lower limbs. Limited-weight-bearing programs protect the injured area from further damage, minimize the loss of aerobic power and capacity, and restore endurance to preinjury levels. When pain control and protection of the injured area are no longer at issue, many types of aerobic or endurance activities can be performed in a gymnasium, including walking or running on a treadmill, stationary cycling, and rowing.

In general, three to five sessions per week, approximately 20 to 60 minutes each, of continuous or intermittent exercise can be done as tolerated. Clearly, the patient's aerobic capacity may limit the duration of the sessions when the program is beginning. The intensity of the exercise can be prescribed and monitored using a relative level (40% to 85%) of the maximal heart rate reserve (see "Aerobic Exercise and Endurance: Improving Fitness for Health Benefits").

Functional Phase

After weeks or months of rehabilitation to restore anatomic form and physiologic function, the patient prepares to return to regular activity, training sessions, and/or competition. The functional phase is important, because the rehabilitation program must be gradually replaced by sports-specific training. In other words, the exercises and the exercise prescription are more functionally oriented and more closely simulate the demands of the patient's sport or activity. The sports-specific demands may vary with the patient's level of skill, sport intensity, and level of competition.

Training. Most of the rehabilitation during the functional phase takes place not in the clinic, but in the gym or sports venue. Although some of the exercises and training programs used in the previous phase may be continued, the functional phase incorporates movements that activate specific muscle groups needed for sports performance. The rehabilitation professional must have a good understanding of the metabolic and neuromuscular demands of the sport to make sound recommendations for training. Muscle activation patterns must be studied so that specific conditioning programs can be prescribed. The degree to which basic physiologic capacities (eg, flexibility, strength, endurance) contribute to performance in a particular sport must be examined and reflected in the recommendations.

A detailed description of sports-specific programs for the functional phase is beyond the scope of this article but is readily available14 (see also suggested readings). The return to training and competition must be planned and performed in collaboration with the conditioning coach and other members of the training team. Many drills and practices include basic skills, such as running, jumping, and throwing or kicking a ball. Individual body segments and joints move in certain coordinated sequences called the kinetic chain. The functional phase focuses on the rehabilitation and conditioning of the entire kinetic chain—not just the upper limbs in sports such as baseball, or lower limbs in sports such as soccer. Plyometrics is one type of functional exercise that is very useful in developing explosive strength. In this type of exercise, a muscle group is rapidly stretched immediately before a concentric action (eg, when a basketball player crouches before jumping for a rebound).

Preventing reinjury. The functional phase is also ideal for preventive work. Return to training and competition will expose the athlete to the same external forces and conditions that were associated with the initial injury. The identification and evaluation of weaknesses in other anatomic areas; deficiencies in physiologic capacities such as flexibility, balance, and coordination; improper sports technique; and lack of protective equipment should all be addressed to reduce the risk of reinjury.

During this phase, the athletes and coaches want to know when to return safely to competition. Subjective clinical guessing should be avoided, and the decision must be based on objective criteria, such as:

  • The absence of pain and signs of inflammation,
  • Full range of motion,
  • Muscle strength symmetry with appropriate strength ratios (injured to uninjured side; agonists to antagonists),15
  • Adequate endurance for the demands of the sport,
  • Tolerance for the use of orthotic devices, and
  • Acceptable technical performance in training.

Other Considerations for All Phases

From a conceptual point of view, rehabilitation takes place simultaneously at various levels. Two other processes are integral in restoring form and function: (1) biological tissue healing and strengthening, and (2) psychological recovery. In addition, various orthotic devices may be used in each phase of rehabilitation.

Tissue healing. Research into the enhancement of tissue healing in the acute and recovery phases could dramatically affect the design of future rehabilitation programs. Limiting fibrosis and enhancing tissue healing as early as possible could allow patients to progress faster in rehabilitation.

Emotional needs. Addressing the active patient's emotional needs is just as important as the physical recovery. The patient may be depressed about the current injury and apprehensive about future injuries. Recognizing the psychological and emotional needs of the injured athlete in each rehabilitation phase will go a long way toward enhancing recovery and assuring the enthusiastic participation of the patient.16

Orthoses. Throughout rehabilitation, orthotic devices can be used to protect the injured area, relieve pain, resist abnormal joint motion after surgery, stabilize limb segments, prevent or correct joint deformity, enhance function, and facilitate the implementation of exercise training. The number and design range of commercially available orthoses is considerable. Shoe inserts and ankle and knee braces are particularly useful as rehabilitation becomes more aggressive in the early initiation of exercise and return to training and competition.17 The role of protective devices during the acute, recovery, and functional phases has grown.

Some ready-made devices can be purchased, but in many instances custom fabrication is necessary. Patients who could benefit from orthotic devices include runners who have abnormal foot and ankle biomechanics (ie, overpronation), basketball and volleyball players who have moderate-to-severe ankle sprains, and football players who have had knee ligament reconstructive surgery.

The Power of Exercise

Exercise is a ubiquitous part of a multistep comprehensive rehabilitation process. Physical rehabilitation takes place simultaneously with the biological healing of injured tissues and the psychological rehabilitation of the patient. Sports medicine practitioners should be familiar with the different types of interventions used to restore strength, flexibility, endurance, and function after injury or surgery. The exercise prescription must be progressively adapted to achieve the best possible outcome.

References

  1. Hurley MV, Jones DW, Newham DJ: Arthrogenic quadriceps inhibition and rehabilitation of patients with extensive traumatic knee injuries. Clin Sci (Lond) 1994;86(3):305-310 [published erratum in Clin Sci (Lond) 1994;86(6):vxii]
  2. Lindh M: Increase of muscle strength from isometric quadriceps exercises at different knee angles. Scand J Rehabil Med 1979;11(1):33-36
  3. Snyder-Mackler L, Delitto A, Bailey SL, et al: Strength of the quadriceps femoris muscle and functional recovery after reconstruction of the anterior cruciate ligament: a prospective, randomized clinical trial of electrical stimulation. J Bone Joint Surg Am 1995;77(8):1166-1173
  4. Enwemeka CS: The effects of therapeutic ultrasound on tendon healing: a biomechanical study. Am J Phys Med Rehabil 120219;68(6):283-287 [published erratum in Am J Phys Med Rehabil 1990;69(5):258]
  5. Krivickas LS: Training flexibility, in Frontera WR, Dawson DM, Slovik DM (eds): Exercise in Rehabilitation Medicine. Champaign, IL, Human Kinetics, 1999, pp 83-102
  6. Schwellnus M: Flexibility and joint range of motion, in Frontera WR (ed), Rehabilitation of Sports Injuries: Scientific Basis. Malden, MA, Blackwell Science, 2021, pp 232-257
  7. Holder-Powell HM, Rutherford OM: Unilateral lower limb injury: its long-term effects on quadriceps, hamstring, and plantarflexor muscle strength. Arch Phys Med Rehabil 1999;80(6):717-720
  8. Urbach D, Awiszus F: Impaired ability of voluntary quadriceps activation bilaterally interferes with function testing after knee injures: a twitch interpolation study. Int J Sports Med 2021;23(4):231-236
  9. Dudley GA, Tesch PA, Miller BJ, et al: Importance of eccentric actions in performance adaptations to resistance training. Aviat Space Environ Med 1991;62(6):543-550
  10. Kraemer WJ: Strength training basics: designing workouts to meet patients' goals. Phys Sportsmed 2021;31(8):39-45
  11. Escamilla RF, Fleisig GS, Zheng N, et al: Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc 192021;30(4):556-569
  12. Mujika I, Padilla S: Muscular characteristics of detraining in humans. Med Sci Sports Exerc 2021;33(8):1297-1303
  13. Mujika I, Padilla S: Cardiorespiratory and metabolic characteristics of detraining in humans. Med Sci Sports Exerc 2021;33(3):413-421
  14. Kibler WB, Chandler TJ: Sport-specific conditioning. Am J Sports Med 1994;22(3):424-432
  15. Croisier JL, Forthomme B, Namurois MH, et al: Hamstring muscle strain recurrence and strength performance disorders. Am J Sports Med 2021;30(2):199-203
  16. Brewer BW, Andersen MB, Van Raalte JL: Psychological aspects of sports injury rehabilitation: toward a biopsychosocial approach, in Mostofsky DI, Zaichkowsky LD (eds): Medical and Psychological Aspects of Sport and Exercise. Morgantown, WV, Fitness Information Technology, 2021, pp 41-54
  17. Munns SW: Knee orthoses, in Physical Medicine and Rehabilitation: State of the Art Reviews. Philadelphia, Hanley and Belfus, 2021;14(2):423-433

SUGGESTED READINGS

Fleck SJ, Kraemer WJ: Designing Resistance Training Programs, ed 2. Champaign, IL, Human Kinetics Publishers, 1997

Frontera WR: Rehabilitation of Sports Injuries: Scientific Basis. Malden, MA, Blackwell Science, 2021

Renström P: Sports Injuries: Basic Principles of Prevention and Care. Boston, Blackwell Scientific Publications, 1993

Renström P: Clinical Practice of Sports Injury Prevention and Care. Boston, Blackwell Scientific Publications, 1994


Dr Frontera is an associate professor at Harvard Medical School and chair of the department of physical medicine and rehabilitation at Harvard and Spaulding Rehabilitation Hospital in Boston. Address correspondence to Walter R. Frontera, MD, PhD, Spaulding Rehabilitation Hospital, 125 Nashua St, Boston, MA 02114; address e-mail to [email protected].

Disclosure information: Dr Frontera discloses no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.


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