Muscular Strength and Endurance 1

Muscles make up more than 40% of your body mass Well-developed muscles can assist with: Daily routines Protection from injury Enhancement of your overall well-being Muscular strength is the amount of force a muscle can produce with a single maximum effort Muscular endurance is the ability to resist fatigue while holding or repeating a muscular contraction 2

Basic Muscle Physiology Muscles consist of individual muscle fibers (cells) connected in bundles Muscle fibers are made up of smaller protein structures called myofibrils sarcomeres (actin and myosin) Myofibrils are comprised of contractile units called sarcomeres (actin and myosin) Proper strength training causes individual fibers to increase the number of myofibrils resulting in hypertrophy Inactivity can reverse this process resulting in atrophy 3

Skeletal Muscle Tissue 4

Sarcomere Gives muscle its striated appearance. –Lighter area: I band –Darker area: A band Smallest contractile unit in the body. –~ 4.0 μm at rest –~ 2.5 μm when contracted Actin –Thin filament Myosin –Thick filament TroponinTropomyosin

Sarcomere A band – Total length of the myosin H zone – Only myosin M line – Center of the sarcomere I band – Only actin Z lines – Ends of the sarcomere

Actin-Myosin Orientation Actin is the “sliding” filament. Myosin heads can attach to the actin binding sites to create a crossbridge. Myosin heads can pivot at the cost of ATP.

Muscle Contraction The Sliding Filament Theory Step 1: Nerve signal arrives at the myofibril and releases neurotransmitter ACh. Step 2: ACH depolarizes the sarcolemma Step 3: Sarcolemma releases Ca 2+ Step 4: Ca 2+ binds to tropomyosin and “pulls” it off of the actin binding site. Step 5: Myosin head binds with actin forming corssbridge.

Muscle Contraction The Sliding Filament Theory Step 6: ATP binds to the crossbridge causing the myosin heads to pivot and the actin filaments to slide towards the M line. Step 7: Crossbridge activation continues as long as Ca 2+ remains high. Step 8: Muscle stimulation stops and Ca 2+ moves back into sarcolemma. Step 9: Calcium removal allows tropomyosin to return to its resting position, covering the actin binding site.

Basic Muscle Physiology Hypertrophy is the development of large muscle fibers Atrophy is the reduction of the size of the muscle fiber due to inactivity or injury Hyperplasia is the increase in the number of muscle fibers. It is not thought that hyperplasia plays a significant role in muscle size in humans. 10

Basic Muscle Physiology Slow-twitch fibers are: Fatigue resistant Don’t contract as rapidly and forcefully as fast- twitch fibers Rely primarily on the aerobic energy system Fast-twitch fibers: Contract rapidly and forcefully Fatigue more quickly than slow-twitch fibers Rely more on the anaerobic energy system 11

Muscle Fiber Types

Motor Units A motor unit is made up of a nerve connected to a number of muscle fibers –Small motor units contain slow-twitch fibers while large motor units contain fast-twitch fibers Motor unit recruitment happens when strength is required; nerves assist with the action –The number and type of motor units recruited are dependent upon the amount of strength required Muscle learning is the ability to improve the body’s ability to recruit motor units 14

Strength Gains Neural factors: –Adaptive alterations in nervous system function that elevate motor neuron output largely account for the rapid and large strength increases early in training. Muscular factors: –An increase in muscular tension with exercise training provides the primary stimulus to initiate the relatively slow process of hypertrophy.

Contributions to Strength Improvements

Types of Muscle Actions

Benefits of Muscular Strength and Endurance Improved performance of physical activities Injury prevention Improved body composition Enhanced self-image and quality of life Improved muscle and bone health with aging Metabolic and heart health 18

Assessing Muscular Strength and Endurance Muscular strength is usually assessed by measuring the maximum amount of weight a person can lift one time (1 RM) –Also can use an estimated maximum test (submaximal lift) –Need to train for several weeks before testing –Retest after 6-12 weeks Muscular endurance is assessed by counting the maximum number of repetitions of a muscular contraction a person can perform to fatigue 19

1RM One-repetition maximum refers to the maximum amount of weight lifted one time using proper form during a standard weight-lifting exercise. –Not always practical –Can be difficult to attain Estimating 1RM  1RM (kg) = X 7-10RM (kg)

Effects of Specific Repetition Ranges

Power Recommendations

Hypertrophy Recommendations

Strength Recommendations

Endurance Recommendations

Creating a Successful Strength Training Program Static (isometric) exercise involves a muscle contraction without a change in the length of the muscle or joint angle An example is pushing against a brick wall Considered useful in strength building after an injury/surgery Isometric contractions are usually held for 6 seconds Dynamic (isotonic) exercise involves a muscle contraction with a change in the length of the muscle Two types Concentric contraction Eccentric contraction 26 Static vs. Dynamic Strength Training

Comparing Static and Dynamic Exercises Static exercises: Isometric exercise Muscle contraction without a change in the length of the muscle or the angle in the joint Require no equipment Build strength rapidly Useful for rehabilitation Dynamic exercises: Isotonic exercise Muscle contraction with a change in the length of the muscle Can be performed without or with equipment Can be used to develop strength or endurance Use full range of motion Are more popular with the general population 27

Training Methods Other Dynamic Methods –Constant and variable resistance –Eccentric loading –Plyometrics –Speed loading – Kettlebells –Isokinetic Other Training Methods and Types of Equipment –Resistance Bands- Medicine balls –Exercise (stability) balls- Suspension training –Pilates- Stones –No-equipment calisthenics 28

Applying the FITT Principle F requency: At least 2-3 nonconsecutive days/week allowing 1 day of rest between workouts –Based on the ACSM guidelines I ntensity: (Amount of Resistance) Strength requires lifting % of your 1 RM; Endurance requires 50-70% of your 1 RM T ime: (Repetitions and Sets) 8-12 reps for strength; reps for endurance; making sure each set leads to overload of that muscle group T ype: (Mode of Exercise) target large muscle groups (8-10 exercises) including opposing muscles –Agonist muscle groups –Antagonist muscle groups 29

Warm Up and Cool Down Everyone should perform a warm-up prior to each weight training session A general warm-up (like walking or easy jogging) and performing light reps of each exercise is recommended before every training session To cool down after weight training, relax for 5-10 minutes by stretching—which could possibly prevent soreness 30

Getting Started and Making Progress First few sessions –Should be devoted to learning the movements –Choose a weight you can move easily 8-12 times; 1 set and rest 1-2 minutes between exercise –Goal is to be doing 1-3 sets of 8-12 repetitions Progress –“Two-for-two” rule –General guideline for increasing weight – increase by approximately 5% of what you are currently lifting –Your rate of improvement depends on how hard you work and your bodies response to resistance training 31

Weight Training Safety Use proper lifting techniques –ACSM recommends a moderate rate for each repetition –Strive to maintain a neutral spine position during each exercise Use spotters with free weights Be alert for injuries –R.I.C.E. principle 32

A Caution About Supplements and Drugs Supplement manufacturers often make claims that their products will promote or enhance sport performance or physique Most of these substances are ineffective and expensive as well as possibly dangerous Before purchasing and using these products, find other resources that document these dietary aids 33