Leverage is an important mechanical principle that influences strength because

Range of Motion and Muscle Strength

The application of heat and controlled stress results in increased tissue extensibility during and shortly after the treatment is applied. This is caused by the viscoelastic properties of connective tissue and the response to preconditioning.12,13 Controlled stress should be applied simultaneously with heating (Fig. 101.e5). This is an ideal preconditioning technique that allows the therapist to determine how compliant the tissues are to controlled stress.57 Depending on the target tissue, superficial or deep heat may be used. Both AROM and passive range of motion (PROM) benefit from preconditioning.

Fig. 101.e5. Application of heat and controlled stress with a hot pack to the elbow as elbow is being stretched into extension.A, The use of a cuff weight on the forearm allows for stress to be placed on elbow and the patient can relax.B, The use of a dumbbell is not recommended because the patient cannot relax, and stress is likely to be put on the wrist, not on the elbow.

The application of heat may also enhance motion by decreasing pain, altering contractile properties of muscle, and increasing blood flow. Heat also decreases the perception of joint stiffness. The application of cryotherapy may enhance motion by decreasing pain and edema. Although joint stiffness may be perceived, the benefits of pain and edema reduction may improve ROM gains. Both AROM and PROM benefit from decreased pain and edema.

Neuromuscular electrical stimulation may be used to augment muscle strength to improve AROM. As previously mentioned, the stronger the contractions are, the greater the strength gains. NMES is particular useful in the presence of disuse atrophy and to promote learning after immobilization. NMES does not take the place of volitional exercise, but it can enhance the AROM gains. NMES should be discontinued when the patient is able to perform a manual muscle test against gravity with minimal resistance (F+ contraction).32,33 The emphasis on volitional exercise will promote the normal muscle physiology in terms of recruitment order and rate coding of the motor units. This may assist coordination and proprioception during functional activities.

Other than the application of heat and controlled stress for preconditioning, physical agents are not used to resolve joint contracture. The authors believe that low-load prolonged stress in the form of orthotic intervention is the first choice to resolve joint stiffness or tendon tightness. NMES has been used in the neurologic population to contract the antagonist to a muscle with spasticity in the hopes of reducing spasticity and increasing motion.58

Muscle Power

Muscle power (Box 3.7) is the ability to produce speed or large forces in a specified amount of time—a vital component of functional performance.8 Examples of functional activities requiring greater muscle power are jumping, snatch lifting, and sprinting. Exercises that address muscle power are performed at greater speed and can involve both initiating and stopping the movement (Clinical Example 3.8). Typically, the larger global movers, which have a higher percentage of glycolytic fibers, are capable of generating greater forces and anaerobic energy production involved in quick movements. When making adjustments in an exercise or functional activity, there is an inverse relationship between speed and resistance. Power exercise, such as plyometrics or snatch lifting, is usually included in therapeutic exercise only after other impairments have been addressed and when adequate functional strength and mobility are available with slower movement. If muscle power deficits are contributing to diminished functional performance, training speed can be increased or the resistance decreased to target physiological changes in glycolytic fibers without placing excessive stress on the connective tissue or muscle.

Scapular Muscle Strength Testing and Special Tests

An alteration in the normal position or motion of the scapula during coupled scapulohumeral movements is called scapular dyskinesis.52 Scapular dyskinesis can be caused by multiple reasons.76 Scapular winging may be considered a type of scapular dyskinesis characterized by significant scapular medial border displacement during shoulder motion. Kelley77 and Leggin and Kelley78 described special tests and muscle testing used in an evaluative scapular muscle algorithm. We describe examination tests to assist in determining if the cause of scapular dyskinesis is from a nerve palsy, glenohumeral instability, or poor motor control.

The patient is first observed in standing for resting winging or scapular displacement and obvious atrophy. If resting winging is noted, the patient is checked for a scoliosis demonstrated by a thoracic rib hump during trunk flexion. Resting medial winging can be caused by an increased thoracic rib angle because the flat scapula’s medial border is displaced. AROM of both shoulders is assessed in the standing position by elevating in the sagittal and coronal planes. Significant scapular winging that normalizes beyond 90 degrees during sagittal plane flexion elevation is typically related to poor motor control of the serratus anterior. If medial winging persists beyond 90 degrees, a long thoracic nerve (LTN) palsy or posterior glenohumeral instability is suggested. Often, normal scapular motion occurs while elevating, but dyskinesiais seen on descent of the arm (usually <90 degrees). As mentioned earlier, “eccentric dumping” is a common finding among many individuals, especially those who performed years of bench pressing or push-ups. Eccentric dumping is a common finding and may or may not be related to shoulder pathology.

Overload

Muscular strength and endurance are developed by the progressive overload principle (e.g. by increasing more than normal the resistance to movement or frequency and duration of activity; American College of Sports Medicine, 2009). Muscular strength is best developed by using heavier weights/resistance (that require maximum or near maximum tension development) with few repetitions, and muscular endurance is best developed by using lighter weights with a great number of repetitions (American College of Sports Medicine, 2009). There are several ways to overload a muscle or muscle group:

add weight or resistance;

sustain the contraction;

shorten resting periods between contractions;

increase speed of the contraction;

increase number of repetitions;

increase frequency and duration of workouts;

decrease recovery time between workouts;

alternate form of exercise;

alternate range to which a muscle is being worked.

The PT can manipulate all the above-listed factors when training the PFM. However, certain important factors are difficult to apply for PFMT (e.g. to add weight and resistance). Plevnik (1985) invented vaginal-weighted cones to make a progression of overload to the PFM (Fig. 6.12). Vaginal cones come in different shapes and weights and are placed above the levator muscle. The patient is asked to start with a weight that she can hold for 1 minute in standing position. The actual training is to try to stay in an upright position with the cone in place for 20 minutes. When the woman is able to walk around with a weight in place for 20 minutes, a heavier weight should replace the one used to make progression in workload. Although correct from a theoretical exercise science point of view this method can be questioned from a practical point of view. In addition, holding a contraction for a long time may decrease blood supply, cause pain and reduce oxygen consumption (Bø, 1995). Many women report that they are unable to hold the cones in place and adherence may be low (Cammu and Van Nylen, 1998; Bø et al., 1999).

Any magnitude of overload will result in strength development, but heavier resistance loads to maximal or near maximal will elicit a significantly greater training effect (American College of Sports Medicine, 2009). Heavy resistance training may cause an acute increase in systolic and diastolic blood pressure, especially when a Valsalva manoeuvre is evoked (American College of Sports Medicine, 2011). This is of importance for PFMT because many women tend to erroneously perform a Valsalva manoeuvre when attempting to perform a PFM contraction. Ferreira et al. (2013) assessed heart rate during PFMT sessions and blood pressure before and after each training session in pregnant women. Heart rate significantly increased during training, but only for a limited time. Increase in blood pressure and heart rate during the training period was within normal ranges. Anecdotally, some women report slight headache, dizziness and discomfort during their first PFMT sessions, and this may be due to an increase in blood pressure or inadequate breathing. Normal breathing during attempts to perform maximum contractions is almost impossible. Therefore, an emphasis on normal breathing between each contraction is important.

Eccentric (lengthening) exercises are effective in increasing muscle strength (Fleck and Kraemer, 2004). However, the potential for skeletal muscle soreness and muscle injury is increased when compared to concentric (shortening) or isometric contractions, particularly in untrained individuals (Fleck and Kraemer, 2004; American College of Sports Medicine, 2009). Eccentric contractions are also more difficult to perform (require more motor skill and muscle awareness) than concentric or isometric contractions, and are therefore not recommended at the beginning of a PFMT programme.

Parascapular Muscle Strength

The role of the scapula in optimal shoulder function is well described.76 Normal scapular mechanics and neuromuscular control of the parascapular muscles allow for (1) proper glenohumeral joint alignment, which enhances the function of the rotator cuff muscles; (2) adequate retraction and protraction along the thoracic wall; and (3) elevation of the acromion for overhead activities such as throwing. In addition, two particular roles of the scapula may affect optimal function of joints distal to the shoulder in the upper extremity. First, the scapula serves as the proximal link in the upper extremity kinetic chain.76,77 This sequencing allows the transfer of kinetic energy and force from the base of support (trunk) to the terminal link (hand). The efficiency of this kinetic chain depends on a stable scapula. Second, the scapula serves as a point of attachment for many muscles known as scapular stabilizers.76 These muscles include the trapezius, rhomboids, levator scapulae, and serratus anterior. Although their contribution to activity varies by task, the serratus anterior muscle has been identified as a primary scapular stabilizer.

The balanced muscle strength and synergistic function of these muscles maintain scapular position or stability during upper extremity tasks.76 Scapular dysfunction may cause injury and dysfunction to distal joints in the upper extremity, particularly the elbow.77,78 Descriptive studies have demonstrated motion loss, strength deficits, and strength imbalances in individuals with LET.24–26,28 Therefore, patients with lateral elbow pain should be examined for ROM and strength impairments of the shoulder girdle so that these impairments can be addressed during treatment as needed.27

Power Training – High-Velocity Resistance Training

Muscle power training (or high-velocity resistance training) has been advocated as a potentially superior form of resistance-based training to enhance physical performance, muscle power, and reduce the risk of falls in older adults [173,174]. Muscle power, which represents the product of force and velocity, is characterized by rapid concentric movements performed at moderate-to-high loads. In a meta-analysis designed to compare different types and intensities of PRT on muscle and functional outcomes in older adults, Steib et al. reported that power training was more effective for improving muscle power and physical performance (chair rising time and stair climbing ability) than traditional PRT [175]. It is hypothesized that this form of training may also provide an enhanced osteogenic effect due to the higher strain rates compared to traditional PRT. In the only study conducted to date, Stengel et al. compared the skeletal response in 53 postmenopausal osteopenic women who participated in either a twice weekly power training or traditional PRT program for 2 years [176, 177]. The training programs were identical except that those women undertaking traditional PRT took 4 seconds for the concentric phase of the movement whereas the power-trained group performed this phase in a rapid explosive fashion. In addition, all women performed gymnastics and home training. Following 12 months of training, total hip and lumbar spine BMD was maintained in the power training group, but decreased in the PRT group [177]. After 2 years, the beneficial effects of power training persisted at the lumbar spine, with a trend for maintenance at the hip [176]. It is important to note that the women in this study had previously participated in a 3-year exercise trial, and thus the response to the exercise training may have been attenuated based on the principle of diminished returns. Nevertheless, these findings provide preliminary evidence that power training might be an effective modality to enhance both bone health and muscle function in older adults.

ACSM Guidelines for Prescription of Strength-Training Exercise

Muscular strength and endurance can be developed with both dynamic and static exercise. Both forms have their indications, but for most individuals dynamic exercise is recommended. Strength exercise should be rhythmic, performed at low to moderate speed, and performed through a full range of motion. Normal breathing should be maintained. Heavy resistance training associated with breath holding can result in dramatic rises in SBP and DBP.

A specific technique for each exercise should be closely adhered to. Both the lifting (concentric) and lowering (eccentric) phases of resistance exercise should be performed in a controlled manner. When possible, training with a partner can provide feedback, assistance, motivation, and safety.

Recommended guidelines for strength training are listed in Table 15.5.

Muscle Performance.

Muscle power, strength, and endurance will influence a patient's ability to achieve leverage and operate or handle tools and environmental controls. Functional muscle testing, such as whether the individual has the strength to handle tools, operate levers, and lift, carry, push, and pull objects as required by their expected roles, can be more useful than examination of strength by measurement of individual muscle performance with manual muscle tests or other approaches. When measuring functional strength, one should note if there are movement variations or muscle substitutions that may increase the risk of injury. Handling tools requires dexterity, power, and control. The patient's method of handling tools should be safe and when work-related, adhere to company guidelines.

The importance of muscle strength

Muscular strength is defined as the ability to exert force on an external resistance. Within sports, an athlete may be required to manipulate their own body mass against gravity (e.g., sprinting, jumping), both their body mass and an opponent’s body mass (e.g., rugby), or that of an external object (e.g., shot put, weightlifting). Ultimately, the force exerted will change, or tend to change, the motion of a body in space. This is based on Newton’s second law of acceleration whereby force (f) is equal to the product of mass (m) and acceleration (a). Based on this principle, the acceleration of a given mass is directly proportional to, and in the same direction as, the force applied. Therefore, muscular strength is the primary factor for producing an effective and efficient movement of an athlete’s body or an external object. This concept is supported by several studies that have found a relationship between muscular strength and performance in a range of motor skills such as sprinting (Comfort et al., 2014; Kirkpatrick and Comfort, 2012; Styles et al., 2015; Seitz et al., 2014a; Wisloff et al., 2004), jumping (Hori et al., 2008; Wisloff et al., 2004), and change of direction (Hori et al., 2008; Nimphius et al., 2010).

Previous literature has indicated that both rate of force development (RFD; change in force divided by the change in time) and power output (rate of work performed) are two of the most important characteristics regarding an athlete’s performance (Baker et al., 2001; Morrissey et al., 1995 Stone et al., 2002). RFD is critical given the time constraints of various sporting tasks. For instance, evidence suggests that it takes individuals a longer period of time (>300 ms) to produce their maximum force (Aagaard et al., 2002; Aagaard, 2003) compared to the duration of jumping and ground contact time during sprinting (Andersen and Aagaard, 2006). Furthermore, athletes have limited time to perform the mechanical work involved with typical sporting tasks and thus, it would seem beneficial to complete the work as fast as possible. For example, an athlete who completes the required work of a given task more quickly may be given a competitive edge compared to their opponent (e.g., beating an opponent in a sprint to the ball in soccer). Given that muscular strength serves as the foundation upon which other abilities can be enhanced, improvements in RFD and power output can result from increases in strength (Suchomel and Comfort, 2017). Furthermore, unless athletes are strong (maximal back squat ≥1.9 × body mass), increasing strength appears to result in greater improvements in performance than ballistic or plyometric training using lighter loads, but with a focus on the velocity of movement (Cormie et al., 2007; 2010a; 2010b; 2011).

MUSCULAR STRENGTH AND ENDURANCE

Muscular strength and endurance training that focuses on exercising specific muscle groups falls under one of three traditional categories:

Swedish remedial/medical gymnastics for health and rehabilitation (Kleen 1921)

‘body building’ for purely aesthetic goals (Chapman 1994)

athletic performance enhancement (Kraemer et al 2002; www.nsca-lift.org).

It is beyond the remit of this text to delve into the specific physiological and biomechanical principles of muscular strength and endurance training. The reader may be required to review, from other texts, some underpinning elements that relate to the evidence and its application to specific populations. The three main types of muscular contraction used in strength and endurance training are of specific note: isotonic, isometric and isokinetic. Some biomechanists may actually question the theoretical constructs of each of these types of contraction but from a practical perspective they are adequate to describe the type of exercise being performed. Typically isotonic activity involves using a fixed amount of weight (e.g. a dumbbell or barbell). In this case, the challenge of moving this given amount of resistance will be dependent upon the angle of the joint(s), which in turn affects the length and tension of the muscle at its tendons. Isometric activity indicates the presence of a muscular contraction where no joint movement occurs. Isokinetic activity refers to muscular work where velocity (linear, or more often, angular) is kept constant throughout the movement. This requires that the resistance changes with the joint angle, which is achieved by employing a device, machine or apparatus. All three types of muscular activity are used in health- and rehabilitation-based exercise.

It is important to remember that improved movement and functionality, rather than muscular strength/endurance, is the most important outcome of any training or rehabilitation programme. Often the evidence reports an improvement in muscular strength but this is only of value if it translates into enhanced functioning or performance. The movement power which can be generated by a person is not just a function of the size and strength of a muscle. It is also significantly influenced by the neurological motor coordination, dynamic balance, stability and ultimately the amount of muscular discomfort an individual is willing to tolerate in producing the given movement. For example, in the chapters on pulmonary and cardiac disease, evidence is presented that increased muscular strength, independent of aerobic exercise training, can enhance walking endurance. The potential mechanisms include improved movement efficiency as a result of improved dynamic stability of the ankle, knee, hip and pelvic-lumbar joints, and the ability to tolerate higher levels of muscle fatigue.