Muscle Strength and Resistance Training for Health and Athletics Chapter 11

Learning Objectives Understand the twitch response of a muscle contraction. Understand how muscle length and joint angle affect force production. Compare and contrast various different muscle actions. Describe the potential health-related benefits of resistance training. Know the basic characteristics of a resistance training program for athletes.

Properties of Muscle Tissue Contractility Irritability Conductivity

Phases of a Muscle Twitch

Summation of Twitches and Tetanus Summation of twitches:  Additive tension from more twitches  Can increase force production Tetanus:  Fusion of individual muscle responses  Occurs when excised muscle is stimulated too frequently and muscle twitch becomes prolonged

Summation of Twitches

Muscle Twitch Responses— Incomplete (A, B, C, and D) and Complete (E) Tetanus

Temperature and Muscle Contraction Heating a muscle: More rapid muscle contraction and relaxation Cooling a muscle: Slower contraction and relaxation Practical application:  Difference may contribute to muscle injury after improper/insufficient warm-up.

Gradations of Response Force of Contractions of Whole Muscles Recruitment:  Varying the number of motor units activated Rate coding:  Increasing or decreasing the rate of firing for the motor units involved

Angle of Pull of the Muscle and the Joint Angle at Which Muscle Action Occurs

Relationship Between Tension and Muscle Length

Gender Differences in Strength Adult females tend to be about 40–80% as strong as males, depending on muscle group. Can be explained by differences in body weight, fat-free body weight, and muscle mass.

Types of Muscle Actions and Examples Isometric:  Pushing against an immovable object, arm wrestling Dynamic constant external resistance (DCER):  Resistance training, power lifting Isokinetic:  Used in rehab settings Concentric:  Biceps curl Eccentric:  Walking, running, squatting

Inverse Relationship Between Amount of Weight Lifted and Number of Repetitions (DCER muscle action)

Relationship Between Torque Production and Range of Motion (Isokinetic muscle action)

Relationship Between Concentric Strength and the Velocity of Muscle Action (Concentric muscle action)

Relationship Between Eccentric Strength and the Velocity of Muscle Action (Eccentric muscle action)

Clinical Application Delayed Onset Muscle Soreness The pain felt 24 to 48 hours after an exercise bout. Eccentric muscle actions are primarily responsible. No treatments prevent or permanently reduce muscle soreness. Individuals adjust quickly to eccentric muscle actions; one bout of activity makes the muscle less susceptible to later tissue damage. How do you handle the experience of feeling sore after an unaccustomed activity?

Physiology of Strength Gains Increase in muscle size could be a result of:  Enlargement of existing muscle fibers (hypertrophy)  Increase in the number of muscle fibers (hyperplasia) Increase in muscle strength could be a result of:  Hypertrophy  Neural adaptations

Hypertrophy Resistance training results in hypertrophy of both fast- and slow-twitch fibers. Increase in contractile protein content of skeletal muscle. Protein synthesis is mediated by complex interactions among hormones—  Influences degree of hypertrophy

Your Perspective Before reading about the 2000 study by Hass et al., would you have said that more sets of a resistance- training program would lead to more strength gains? What have you seen from your own experience, or those of your friends, from lifting weights at the gym? Do more reps mean more gains? What advice would you give to someone who wants to improve health and fitness through resistance training?

Cross-Education Resistance training of one limb results in strength training in that limb and in corresponding untrained contralateral limb.  Strength increase in untrained limb is about 60% of increase in trained one. Health-related implications:  Maintaining muscle tone  Preventing atrophy in immobilized muscles

Goals of Health-Related Resistance Training Programs 1. Make activities of daily living less physiologically demanding and stressful 2. Effectively manage, reduce, and prevent chronic diseases (e.g., osteoporosis, type 2 diabetes mellitus, obesity)

Health Benefits of Resistance Training Increased bone mineral density Favorable changes in body composition Increased functional strength for daily living Improved insulin sensitivity Increased basal metabolic rate Decreased diastolic blood pressure Reduced risk of low back pain Decreased risk of injury during physical activity Improved blood lipid profiles

Resistance Training Prescription Healthy adults:  2–4 sets of 8–10 multi- joint exercises, at least one for each major muscle group  8–12 reps  2 to 3 days a week (48 hrs between sessions involving same muscle group) Older individuals:  Same program, but reduce the resistance and increase the reps (10–15)

ACSM Recommendations for Increasing Muscular Strength in Healthy Adults

ACSM Recommendations for Increasing Muscle Size Through Hypertrophy

Basic Principles of Resistance Training for Athletes Specificity Overload Progression Periodization

Linear Periodization Model

Recommendations for Designing a Resistance Training Program for Athletes Train at least 3 days/wk, with minimum of 24 hrs of rest between sessions All major muscle groups Appropriate muscle balance Periodize training to vary volume and intensity Recovery periods No more than 2 exercises per body part; different exercises per body part throughout week (continued)

More Recommendations Limit specific large-muscle group exercises to 2 times/wk. Warm-up sets involving very light resistance. Perform large-muscle group exercises first. 4-day-week training protocol; divide the selected lifts into two groups: (a) chest and shoulders, and (b) back and legs. Use multi-joint and Olympic-style lifts with free weights and isolated movements on resistance machines.

ACSM Recommendations for Increasing Muscular Power Through Resistance Training

Plyometric Training Used to increase explosive muscular power Involves stretching a muscle through an eccentric phase followed by a forceful concentric muscle action Improves performance in anaerobic activities Beneficial for sports requiring high level of explosive power (e.g., track and field, football, volleyball, basketball) Examples:  Depth jumps from an elevated stand, leaping over objects, hopping, overhead throw, lateral toss

Concurrent Strength and Endurance Training Improvements in both muscular strength and aerobic capabilities. Increases in muscular strength tend to be less than those that result from strength training alone. No difference in the increase in aerobic power that results from concurrent strength and endurance training vs. endurance training alone.

Overtraining and Detraining Overtraining:  Staleness or burnout  Possible cause: too many competitions, poor dietary choices, stress, not enough rest  Most effective cure: rest Detraining:  Cessation of training  Characterized by an immediate decrease in strength  May be able to maintain training- induced strength gains with only 1 session per week

Where to Learn More Physical factors behind the action potential:  potential.html potential.html Strength training:  Plyometrics: 

ACSM CHFS Certification Standards— and Knowledge of twitch, summation, and tetanus with respect to muscle contraction. Knowledge of the physiological principles involved in promoting gains in muscular strength and endurance.  With the cross-education effect, why do you think training of the right leg increases strength in the left leg but not in the left arm?