Resistance exercise

HEALTH PROMOTION AND PHYSIOTHERAPY

Introduction to Resistance exerciseSubhanjan Das

Definitions:Resisted exercise: Resisted exercise is any form of active exercise in which dynamic or static muscle contraction is resisted by an outside force applied manually or mechanically.

Strength: Muscle strength is the greatest measurable force that can be exerted by a muscle or muscle group to overcome resistance during a single maximum effort.Power: Muscle power is defined as work produced by the muscle per unit of time. Power= forceXdistance/timeEndurance: It is the ability to perform low intensity repetitive or sustained activities over a prolonged period of time.

Types of muscle works:Isometric muscle work: in this type of muscle work there is increase in tone of the muscle without any change in the muscle length.e.g. isometric strengthening for neck extensors: the clasped hand behind the head is pushed back by the head. No movement of the head or neck occurs but the tone of neck extensors increases.

Isotonic muscle work: in this type of muscle work there is change in length of the muscle while it maintains an even tone throughout the contraction period. This is of two typesConcentric work: here the origin and insertions come closer and the muscle length shortens.e.g getting up from a chair: knee and hip extensors contract concentrically to bring about extension in these two joints.Eccentric work: here the origin and the insertion go away from each other and the muscle length increases.e.g. sitting on a chair from standing: : knee and hip extensors contract eccentrically to bring about flexion in these two joints.

In concentric contraction the force generated by the muscle is greater than the resistance.In isometric contraction force generated by the muscle is equal to the resistance.In eccentric contraction the force generated by the muscle is lesser than the resistance.

Principles resistance exercisePrinciple of overload:If muscle performance is to improve , a load that exceed the metabolic capacity of the muscle must be applied; that is a muscle must be challenged to perform at a level greater than to which it is accustomed.Overload can be applied by increasing the intensity or volume. In strength training the intensity is increased where as in endurance training the volume i.e. frequency, repetitions and time is increased.

SAID (Specific Adaptation to Imposed Demand ) principle:Adaptations produced by the training are highly specific to the nature of the stimulus or overload applied.SAID applies to all the systems of the body.The adaptations are specific to strength, power, endurance, functional activity, joint angle, sequence of muscle activations, energy systems and virtually all other variable present.

Principle of Reversibility: The adaptations achieved through resistance exercise persist as long as the resistance exercise is performed regularly and go back gradually to the pre exercise levels once the training is stopped. This means the effects of resistance training are reversible.

Inter individual variability:Every individual responds to resistance exercise in a different way, thus similar stimuli may bring about a lot of improvement in one patient and no improvement in others.

Initial values:

Ranges of muscle workFULL RANGE:Contraction takes place throughout the range, starting from fully stretched position in case of concentric contraction and from fully shortened position in case of eccentric contraction. Full range contractions are normally needed only during emergencies (e.g. preventing a fall).Uses: Maintain joint mobilityIncrease circulationPreparation for situations when power & mobility is needed.

Ranges of muscle workINNER RANGE:The muscle either shortens concentrically from half way of its range, or is lengthened by eccentric contraction from fully contracted state to halfway.Uses:Gain or maintain joint movement in the direction of muscle pull.Train some extensors that stabilize joints. E.g. Knee: VMO strengthening

Ranges of muscle workOUTER RANGE:Concentric contraction from fully stretched position to halfway range and eccentric contraction from halfway range to the fully contracted positionUses:Very useful for initiation of contraction (stretch reflex acts better) Muscles contract more forcefully (Frank sterling law)

Ranges of muscle workMIDDLE RANGE:

In this range of muscle work the muscles neither reach the fully contracted range nor are fully stretched, but moves only in the range inbetween. This range is most functional and generally most efficient (angle of pull near 90 degree)USES:Maintenance of muscle tone and normal power .

Group action of musclesPrime movers/ agonistsAntagonistsSynergistsfixators

Prime moversThey are the muscles who bring about the movement by contraction. They are responsible for most of the forces generated in the movement.E.g. for shoulder abduction deltoid is acting as the prime mover.

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AntagonistsThese are the muscles that are opposing group of prime movers. They relax and are lengthened (either passively or eccentrically) to allow controlled movement.E.g. shoulder adductors lengthen passively during abduction, knee extensors lengthen eccentrically during knee flexion in standing to sitting

SynergistsThey work or relax to modify the movement of the prime movers. They may alter the direction of pull of prime mover or when a multijoint muscle is the prime mover, fix the joint where movement is not required in a position of advantage.E.g. rotator cuff in shoulder alters the pull of deltoid and creates abduction. Without them the deltoid would create an upward translation.While making a fist the finger flexors are agonists, they are multijoint muscle and can flex the wrist too. The wrist extensors act as synergist and fix the wrist in extension so that the force of prime movers are used only in fingers.

Indications Curative: Muscle: weakness or paralysisBone: to increase densityAerobic system: improves aerobic capacityOther connective tissues: improve pliability and strength

2. Preventive: to preserve muscle power in all the conditions where muscle weakness is anticipated.To live a healthy life with high levels of fitness.3. Preparative: to prepare for some specific activity where the adaptations of resistance exercise will be useful, e.g training for arm muscles of a boxer will prepare him for a better performance.4. Recreative: various form of resistance training is used as sports and recreation activity, like body building.

Causes of muscle weakness & paralysisLesions in motor pathway:Lesion in brain / spinal cord: spastic paralysis e.g stroke, spinal cord injuryLesions in AHC: flaccid paralysis: e.g polioLesion in peripheral nerve: flacccid paralysis, e.g. Saturday night palsyII. Lesion affecting muscle tissue:Degeneration, e.g. muscular dystrophyIschemia e.g. VICScarring e.g. cut injuries

Causes of muscle weakness & paralysisIII. Disuse of normal nerve and muscle: can occur because:Muscle inhibition by pain or spasmRest:Splintage, immobilisation or bed restHypoactive patientIV. Other causes:Systemic illness: constitutional diseases like RA causes marked muscle wastingFunctional: apparent muscle weakness for secondary gain.

Adaptations of resistance exerciseI.Neural adaptation:Starts within 4 weeks of regular training. Caused by decreased CNS inhibition, decreased GTO sensitivity & changes in NMJIncreased no. of motor unit recruitmentIncreased rate of firingSynchronized firing

Adaptations of resistance exerciseII. Skeletal muscle adaptation:

A. HYPERTROPHYIt is increase in the muscle bulk without increase in the no of muscle fibers, due to increased myofibril volume.Starts between 4-8 weeks of resistance training.Caused by increased protein synthesis and reduced protein degradation.Maximum hypertrophy in high volume moderate resistance exercises performed eccentrically.

Adaptations of resistance exerciseB. HYPERPLASIAIt means increase in the no of muscle fibers.A small portion of muscle fibers may increase in no by longitudinal splitting.C. VASCULAR & METABOLIC ADAPTATIONSDecreased capillary bed densityDecreased mitochondrial densityATP & CP storage increaseMyoglobin storage increasesCPK & Myokinease increase

Adaptations of resistance exerciseIII. Bone:Minimizes or prevents loss of bone mineral density.Can be used for the treatment of osteoporosis/ osteopeniaIV. Connective tissueTensile strength of tendons ligaments and connective tissue in muscle increses

DETERMINANTS OF RESISTANCE TRAININGFrequencyIntensity TimeTypeAlignment & StabilizationVolumeperiodizationRest intervalSequencingIntegration to functional activities(FITT pas vir)The determinants are interdependent for a successful regime

frequencyNo. of exercise sessions per day or per week.Depends on the goal or adaptaion desired, should be set in accordance with intensity and volume.Importance:Decides the rest time between two sessions of exercise. The rest is needed to recover from the fatigue and for the adaptations (e.g. protein sysntesis) to occur.Higher the intensity and volume lower should be the frequency, as strong exercises creates microtrauma which needs time to recover.In immediate post surgery conditions short sessions of exercise is given several times a day whereas high intensity exercise for body building are usually performed 3-5 sessions a week.

Frequency contd.Excessive frequency: progressive fatigue, decline in performance, overuse injuryInadequate frequency: no or minimal adaptaions

Intensity/ exercise load/ training loadThe intensity is the amount of resistance/ load imposed on the contracting muscles during each repetitions of an exercise.2 types: Maximalmaximal intensity resistance of a muscle is the highest resistance a muscle can withstand, higher than maximal intensity being beyond the muscles capacitySubmaximal submaximal intensity resistance is a resistance that is lower than the maximal intensity, usually some percent of the maximal intensity (between 30 to 80%)

Repetition maximumRM is a method of quantifying exercise intensity, Givenn by DelormeDefinition:A repetition maximum is defined as the greatest amount of weight a muscle can move through the available ROM a specific no of times.1 RM for a muscle is the maximum weight (resistance) with which the muscle can contract through full/ available ROM for one time. The muscle will be unable to perform the repetition for a second time .10 RM for a muscle is the maximum weight (resistance) with which the muscle can contract through full/ available ROM for 10 times. The muscle will be unable to perform an 11th repetition .

Uses of RMTo document a baseline measurement of dynamic strength of a muscleTo identify an exercise load to be used during exerciseTo find out prognosis in reassessment and alter the exercise regime accordingly.

How to measure 1RMMeasured by repetitions to fatigue method using equations/ charts.Various equations and charts are available eg. 1 RM=(No of reps/30+1)X weight usedExample: if one lifts 15 kg for 20 times, 1RM= ?For reps to fatigue the muscle is warmed up and stretched and then given a weight (preferrably free weight) which can be performed comfortably over 5 repetitions. The no of repetition the candidate can perform before fatigue is noted.

Training zoneThe amount of resistance to be used in a training program is usually a percentage of 1RMFor sedentary: 30-40% of 1 RMFor untrained healthy individual: 60-70% of 1 RMFor highly trained: 80-95% of 1 RM

Time/duratiionThe duration of a resistance training regime is the total no of weeks or months during which the exercise program is carried out.Duration determines the adaptations: