Regaining Muscle Strength & Endurance

Regaining Muscle Strength & Endurance Rehabilitation Techniques for sports medicine and athletic training: william e. prentice

introduction • Following musculoskeletal injury there will be some degree of impairment in muscular strength and endurance • Rehabilitation program must focus on regaining and improving strength and endurance • Through thorough evaluation; identify weak links and address them during rehabilitation program • Injured area and along kinetic chain

introduction • Muscle Strength: ability for muscle to generate force against some resistance • Weakness or imbalance can impair normal functional movement • Muscle Endurance: ability to perform muscle contractions against some resistance for an extended period of time • As strength increases there is a corresponding increase in endurance • When Developing rehab. Plan, you must have an understanding of what you are trying to accomplish

Types of skeletal muscle contraction • Isometric: muscle contracts to produce tension, but there is no change in muscle length • Considerable force can be generated even though no movement occurs • Concentric: Muscle shortens in length, while tension increases to overcome or move some resistance • Eccentric: Muscle lengthens while producing tension • Resistance is greater than the muscular force being produced

Types of skeletal muscle contraction • Recommended that strengthening programs include exercises that strengthen muscles in a manner in which they contract functionally • All muscles function concentrically, eccentrically, and isometrically in 3 planes of motion • Rehab plan may begin with single joint, single plane isolated contractions, but should progress to multi-plane, multi-joint functional movement

Factors that determine levels of muscular strength, endurance & Power • Size of muscle • Number of muscle fibers • Neuromuscular efficiency

Factors that determine levels of muscular strength, endurance & Power • Size of muscle • Muscular strength is proportional to the cross-sectional diameter (CSD) of muscle fibers • Greater the CSD, or bigger a particular muscle is, the stronger it is, thus more force it is capable of generating • Size of muscle can increase with resistance training • Hypertrophy: increase in muscle size • Atrophy: Decrease is muscle size

Factors that determine levels of muscular strength, endurance & Power • Number of muscle fibers • Strength also determined by the number of muscle fibers within a given muscle • Inherited characteristic • Person with a large # of muscle fibers has the potential to hypertrophy to a much greater degree than someone with relatively few fibers • Through resistance training we can increase size of muscle fibers, but NOT the number of muscle fibers within a given muscle

Factors that determine levels of muscular strength, endurance & Power • Neuromuscular Efficiency • Strength is also directly related to the efficiency of the neuromuscular system and the function of the motor unit in producing muscular force • Motor unit: motor nerve and group of muscle fibers it innervates • Electrical impulse from CNS through motor nerve to muscle fibers it innervates cause muscle contraction • Initial increases in strength during 1st 8 to 10 weeks of a resistance training program can be attributed primarily to increased neuromuscular efficiency • Increase in # of motor units being recruited • Firing rate of each motor unit • Synchronization of motor unit firing

Muscle Fiber and Motor Unit

Fast-Twitch vs. slow-twitch • All muscle fibers in a particular motor unit are either fast-twitch or slow-twitch • Each has distinctive metabolic and contractile capabilities • Slow twitch • Type I or slow oxidative fibers • First on and last off • Resistant to fatigue, however time required to generate force is greater • Associated primarily with long duration aerobic-type activities

Fast twitch vs. slow-twitch • Fast –twitch • Capable of producing quick, forceful contractions, but fatigue more rapidly than Type I • Useful in short term, high intensity activities which mainly involve anaerobic system • 2 types • Type IIA or fast-oxidative-glycolytic • Second on Second off • Type IIB or fast-glycolytic • Last on and first off • Fatigue rapidly • “true” fast twitch fibers

Fast-twitch vs. slow-twitch • Ratio in muscle • Within a particular muscle there are Type I and II muscle fibers • Ratio of types varies with each person • Muscles whose primary function is posture against gravity tend to have more slow twitch • Muscles that produce powerful, rapid, explosive strength movements tend to have a higher percentage of fast-twitch

Fast-twitch vs. slow-twitch • Ratio in muscle continued • Genetically determined and may play a part in determining ability for given sport activity • Must recognize what muscle fibers you are targeting during your rehabilitation plan and develop appropriate exercises • Can improve metabolic capabilities of each type through specific strength and endurance training • Can change Type IIB to Type IIA, but cannot change type II to Type I or vice versa

Physiology of Strength Development • Muscle Hypertrophy • Increase in size of muscle fiber • Theorized that dormant capillaries might become filled with blood to meet demands of increased blood flow from resistance training • Theorized that there is an increase in size and number of actin and myosin (myofilaments) within the muscle fiber • Thus muscle fibers increase in CSD • Hyperplasia: Increase in # of muscle fibers • Seen only in animal studies and not generalized for humans

Physiology of Strength Development • Reversibility • If resistance training is discontinued or interrupted, muscle will atrophy, decreasing strength and mass • As little as 48 hours • Consistent resistance training is essential to maintain strength and size

Techniques of Resistance Training • Overload Principle • For a muscle to improve strength it must be forced to work at a higher level than it is accustomed to. • Must be overloaded • Without overload, strength can be maintained with low to moderate intensity resistance training, but will not increase • Might be good training method for muscular endurance • In rehabilitation, progression may be limited by tissue healing and athletes pain, however most injuries will result in atrophy or be caused by atrophy of one or multiple muscles, so hypertrophy will lilely be goal of rehab. plan

Techniques of Resistance Training • SAID Principle • Specific Adaptations to Imposed Demands • When body is subjected to stress and overloads of varying intensities, it will gradually adapt over time, to overcome demands placed on it • Must apply term to different phases of rehab. • What are you trying to accomplish? BE SPECIFIC • For example: When reconditioning a basketball player would you want to have them run a mile?

Techniques of Resistance Training • Isometric Exercise • Used in early phases of rehabilitation when full ROM exercises exacerbate symptoms or could cause further injury • 10 second hold for 10+ repetitions per hour recommended • Can be useful in strength increases at specific point in ROM • Submaximal to maximal intensities • Must be careful with increase in intrathoracic pressure (Val Salva) that occurs with maximal contractions • Also used by weight lifters to help increase strength at “sticking point” during a specific lift

Techniques of Resistance Training • Progressive Resistive Exercises(PRE) • Exercises that strengthen muscles through a contraction that overcomes some fixed resistance • Dumbbells, machines, elastic tubing • Uses isotonic contractions: contractions in which force is generated while muscle is changing length • Concentric and eccentric contractions

Concentric vs. Eccentric • Can generate more force against resistance with an eccentric contraction • Movement requires lower level of motor unit activity to achieve certain force than a concentric contraction • With fewer motor units firing to produce specific force additional motor units can be recruited to generate increased force • Eccentric contractions are less resistant to fatigue because requirement for Oxygen is less

Concentric vs. Eccentric • Eccentric contractions during rehabilitation have recently received considerable emphasis in research • Eccentric contractions critical in deceleration of limb motion, especially during high velocity dynamic activities • Strength deficits or inability to tolerate these forces may predispose a person to injury • Should focus on concentric and eccentric exercises during rehabilitation • Concentric movement: 1-2 seconds • Eccentric contraction: 2-4 seconds • Ratio of concentric to eccentric should be approximately 1:2 • Muscle will fatigue more rapidly concentrically than eccentrically • Eccentric loading can assist in increasing tensile strength of healing tissue

Progressive Resistive Exercises(PRE) • Repetitions: number of times a specific movement is repeated • Repetition Maximum: Maximum # of repetitions at a given weight • Set: A group of repetitions and recovery intervals • Intensity: Amount of weight or resistance lifted • Recovery Period: rest interval between repetitions and sets • Volume: Amount of work (reps x sets) in a given training session • Frequency: # of training sessions in a week’s period • Periodization: preplanned, systematic variations in training specificity, intensity and volume organized in periods or cycles • Used in strength and conditioning, but should also be used in rehabilitative setting

Periodization Model for Resistance Training

Free weights vs. Exercise machines • Exercise machines • Can be safer and easier to use • Design constraints often only allow single plane motions • Not very functional • Free weights • Element of neuromuscular control to stabilize weight from moving in different directions • May decrease amount of weight lifted compared to machine • Machines have restricted motion • Can incorporate multi-joint, multi-plane functional movements

Surgical tubing/theraband • Widely used in rehabilitation • Can perform isolated strengthening exercises or multi joint, multi-plane exercises • Easy for athlete to use at home • Can purchase different resistance levels identified by colors • Athlete can adjust resistance by increasing or decreasing tension on the band • Movement can occur in multi planes simultaneously • Exercise against resistance in more functional movement planes

Plyometric Exercise • Incorporated in later stages of rehabilitation • Hops, bounds, depth jumps, weighted throws and rotations • Specific exercises that require a rapid stretch of a muscle eccentrically followed immediately by a rapid concentric contraction • Increase ability to use stored elastic energy • Affected by time, magnitude of stretch and velocity of stretch • Facilitate and develop a forceful, explosive movement over a short period of time • Help in developing eccentric control in dynamic movements

Open vs. Closed Kinetic Chain exercises • Open chain: foot or hand is not in contact with ground or some other surface • Closed Chain: Foot or hand is weight bearing or fixed on ground or surface • Most functional activities involve some aspect of weight bearing for the feet or hands • May start with open chain exercises, but must progress to closed chain exercises to optimize rehabilitation • Closed chain exercises will transmit forces throughout kinetic chain • Strengthening and stabilization of multiple muscles and joints

Conclusion • During rehabilitation must incorporate muscle strength and endurance exercises • Assist in tissue healing by realignment of scar tissue and increasing tensile strength • Identify weaknesses and address during rehab program • Strength deficits or atrophy from the injury or that may have predisposed athlete to the injury • Use progressive resistance exercises following periodization, overload and specificity principles when developing rehab program • Communication with the athlete is essential to proper progression of resistive exercises • Pain and swelling can help guide your progression

Regaining Muscle Strength & Endurance