Strength Training Patricia A. Deuster, PhD, MPH Uniformed Services University Outline of Presentation • Define strength training; • Factors affecting force generation; • Development of muscle strength; • Muscular power and endurance; • Approaches to strength training; • Benefits of strength training; • Designing a strength training program. Objectives • Identify strength training terms; • Discuss trends in the prevalence of strength training; • Discuss factors that determine muscle force development; • Identify and differentiate skeletal muscle fiber types; • Discuss strength training terms and how to develop a strength training program; • Describe benefits of strength training. Strength Training Terms • Progressive Overload • Adaptation • Specificity and Variation • Muscular Strength • Periodization • Muscular Hypertrophy • Loading • Muscular Power • Training Volume, Impulse • Muscular Endurance • Exercise Selection and • Motor Performance Order • Rest Periods and Frequency • Muscle Action and Velocity of muscle action Kraemer et al; American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2002 Feb;34(2):364-80. Healthy People 2010 Objective and Strength Training • Increase to 30% the proportion of adults who perform physical activities that enhance and maintain muscular strength and endurance on > 2 days per week; • Also recommended by the American College of Sports Medicine. Prevalence of Strength Training by Gender Prevalence of Strength Training by Year 40 Men 32 Women 24 2010 Goal 16 8 0 1998 1999 2000 2001 2002 2003 2004 Year Prevalence of Strength Training by Ethnicity Prevalence of Strength Training by Year 40 30 2010 Goal White Men Black Men 20 Hispanic Men White Women Black Women 10 Hispanic Women 0 1998 1999 2000 2001 2002 2003 2004 Year Factors Affecting Muscular Force Generation • Muscle Architecture • Muscle Mechanics • Length-Tension Relationship • Muscle Fiber Types • Force-Velocity Relationship • Electromechanical Delay Muscle Architecture • Long axis of muscle determines arrangement of muscle fibers • Reflects muscle force and power • Two basic types – Fusiform: spindle shaped – Pennate: fan-shaped Muscle Fiber Architecture Pennation Effects on Force and Fiber Packing • Pennation allows for packing a more fibers into a smaller cross-sectional area than parallel fibers. • = surface pennation angle Fusiform Fiber Arrangement Fa = force of contraction of muscle fiber parallel to long axis of muscle Fa SFa = sum of all muscle fiber contractions parallel to long axis of muscle Pennate Fiber Arrangement Fa = force of contraction of muscle fiber parallel to long axis of muscle Fa Fm Fm = force of contraction of muscle fiber = pennation angle Fa = (cos )(Fm) SFa = sum of all muscle fiber contractions parallel to long axis of muscle Muscle Mechanics • Active Force through contractile elements: actin and myosin mechanism; • Passive Force through elastic elements: – Series elastic elements (tendons) smooth out force of contraction and reduce effects of external forces from overloads – Parallel elastic elements (fascia) absorb energy input externally if muscle is stretched beyond normal "resting" length. Muscle Mechanics PE = Parallel elastic component SE = Series elastic component CE = Contractile element Fibers in series • The range of motion Force production modest, and amount of force a but large range of muscle can generate is shortening. largely determined by Fibers in parallel the arrangement of Force production high, but the muscle fibers minimal range of shortening. Length-Tension Relationship • Force generation optimized when muscle is slightly stretched. • Due to contribution of elastic components of muscle (primarily the SEC) QuickTime™ an d a TIFF (Uncompressed) decompressor are need ed to see this p icture . Human Muscle Fiber Types Other Terminology Slow Twitch Fast Twitch Type Ia Type lla Type lld(x) Aerobic Capacity HIGH MED/HIGH MED Myoglobin Content HIGH MED LOW Color RED RED PINK/WHITE Fatigue Resistance HIGH MED/HIGH MED Glycolytic Capacity LOW MED MED/HIGH Glycogen Content LOW MED HIGH Triglyceride Content HIGH MED MED/LOW Myosin Heavy Chain (MHC) MHCIb MHCIIa MHCIId(x) Human Muscle Fiber Types Characteristics Names ST FTa FTd/x SO FOG FG Fibers/Motor Neuron 10-180 300-800 300-800 Motor Neuron Size Small Large Large Nerve Conduction Velocity Slow Fast Fast Contraction Speed (ms) 110 50 50 Type of Myosin ATPase Slow Fast Fast SR Development Low High High Motor Unit Force Low High High Comparison of Maximal Shortening Velocities Between Fiber Types Force and Types of Muscle Contractions Concentric Eccentric Isometric Isotonic Contractions • Muscle changes length (changing angle of joint) and moves a load. • Two types of isotonic contractions – Concentric: Muscle shortens as it contracts – Eccentric: Muscle lengthens as it contracts Isometric Contractions • Tension increases without changes in length • Occurs if the load is greater than the tension the muscle is able to develop Force-Velocity Relationship • Maximal force developed by muscle is governed by its shortening or lengthening velocity - holds true for all muscle types Force Velocity Relationships • Concentric: CON Ability to develop force is greater at slower contraction velocities - allows greater time for cross-bridges to generate tension Force-Velocity Relationship • Eccentric: ECC Greater force with increasing velocity/ acceleration, due to lower metabolic cost, greater mechanical efficiency and greater contribution from series elastic components. Force-Velocity Relationship Electromechanical Delay • Time between arrival of neural stimulus and tension development by muscle • Varies among muscles (20-100 msec) • Short EMDs produced by muscles with high percentage of FT fibers • Not affected by muscle length, contraction type, contraction velocity, or fatigue Electromechanical Delay Development of Muscle Strength • Maturation • Training Maturation and Strength Factors contributing to muscle 100% Adult potential strength during maturation Lean body mass Theoretical fiber type differentiation Testosterone Neural myelination development Birth Puberty Adult Strength primarily Consolidation Optimal strength via motor patterns of strength potential factors Kraemer, 1989 Adaptations to Strength Training • Physiological Adaptations – muscle fiber size and strength; – connective tissue density and bone integrity. – Muscle fiber type conversion? • Neural Adaptations – recruitment of motor units; – in firing rate of motor neurons; – Improved synchronization in motor neuron firing; – Counteraction of autogenic inhibition to allow greater force production. Skeletal Muscle Adaptations • Muscle Fiber Size • Muscle Fiber Type Conversion • Muscular Strength Muscle Fiber Hypertrophy • Increase in numbers of myofibrils and actin and myosin filaments – Allows more cross-bridges. • Increases in muscle protein synthesis during post-exercise period. • Testosterone plays a role in promoting muscle growth. • High intensity training may promote greater fiber hypertrophy than low intensity training. Muscle Fiber Hyperplasia • Muscle fibers may split in half with intense weight training. • Each half may then increases to size of parent fiber. • Satellite cells may also be involved in skeletal muscle fiber generation. • Clearly shown in animal models, but in only a few human studies. Process of Strength Gains • Early strength gains • Long-term strength influenced by neural gains due to muscle factors. hypertrophy. Mechanisms of Strength Training Adaptations • Mechanical stimuli – CON-only training equally effective as ECC, despite mechanical advantage of ECC (greater forces, muscle damage, etc) • Metabolic Stimuli – Greater metabolic costs with CON – Build-up of metabolic by-products may enhance release of anabolic hormones and lead to greater motor unit activation. Muscular Power • Power = Work/Time = – (Force X Distance)/Time = – Force X Velocity • Maximal power occurs at: – ~ 1/3 max velocity – ~ 1/3 max concentric force • Affected by muscular strength and movement speed; • Main determinant of performance for throwing, jumping, changing direction, and striking activities. Force-Power Relationship • Power generated is greater in muscle with a high % of fast-twitch fibers at any given velocity of movement; • Peak power increases with velocity up to movement speeds of 200-300º•sec-1 – Force decreases with increasing movement speed beyond this velocity Force-Power Relationship Muscle Load and Shortening Velocity Maximum • Max velocity at minimum load Power • Max load at velocity 0 Velocity of Contraction (cm/s) 30 Power (force x velocity) • Power = 0 at 0 load and max load 20 • Maximal power of muscle occurs at 1/3rd max load, or where 10 Velocity X Load is greatest. 0 0.33 0.66 max Muscle -10 Load opposing contraction lengthening -20 Muscular Endurance • The ability to exert tension over a period of time. – Constant: gymnast in iron cross – Varying: rowing, running, cycling • Length of time dramatically affected by force and speed requirements of activity. • Training involves many repetitions with light resistance. Approaches to Strength Training • Static (isometric) actions • Dynamic actions – Free weights – Gravity dependent – Variable resistance – Isokinetic actions – Plyometrics • Other – Neuromuscular electrical stimulation Free Weights • Gravity dependent • Resistance pattern constant or variable • Concentric and eccentric action of same muscles: antagonistic muscles not utilized • Momentum may be factor in resistance pattern Gravity Dependent Machines • Universal Gym • Resistance moves upward • Round pulleys changes direction of resistance • Constant resistance Variable Resistance Machines • Nautilus • Cam design creates variable resistance • Designed to mimic strength curve Isokinetic Devices • Biodex, Cybex, Orthotron, and hydraulic equipment • Accommodating resistance • Constant velocity Plyometrics • Used to develop jumping, sprinting and explosive power; • Muscle is contracted eccentrically then immediately concentrically (muscle is lengthened before it is contracted); • Should not be done more than 2x/wk; • Requires 100% effort for all movements; • Need adequate rest time between exercises to recover: 1 to 5 work:rest ratio. Other Devices • The body – pushups, sit-ups, pull- ups • Pushup variations • Sit-ups, curl-ups - changing resistance • Pull-ups – pronated vs. supinated grip Neuromuscular Electrical Stimulation • Characterized by low volt stimulation targeted to stimulate motor nerves to cause a muscle contraction. – Brain sends a special signal via a nerve impulse to muscle "motor point" causing muscle to contract and exercise just as if it had received a signal from the brain. • TENS is designed to stimulate sensing nerve endings to help decrease pain. Strength Training Benefits • Reduces: – # of injuries – Severity of injuries – Rehabilitation time • Increases and Maintains: – Strength and power – Endurance and stamina – Lean body mass • Develops: – Mental focus & toughness Designing Strength Training Programs • Identify goals, depending on sport and equipment available; • Carry out strength testing to select appropriate resistance levels; – Repetition Maximum or RM - Maximum amount of weight lifted for a given number of reps – 1RM = amount of weight that can be lifted only one time. Determining a 1RM • Warm up for 10 minutes then select weight light enough for > 10 reps; • Perform 12 - 15 reps, then rest 2 minutes; • Increase weight 2% - 10%, perform 10 - 12 reps, then rest 3 minutes. • Increase weight 2% - 10%, perform 6 - 8 reps then rest for 3 minutes. • Increase weight 2% - 10%, perform 5 reps - should be close to 5RM; • Multiply 5RM weight by 1.15 to get 1RM. Key Training Principles Overload Specificity Progression Individualism Adaptation Maintenance Periodization Periodization • Training technique that involves altering training variables over a specific period to achieve well-defined gains in strength, endurance, and overall performance. • Cycle of phases: activation (getting ready for new activity), strength development, muscular endurance development, and active recovery. Acute Program Variables Muscle Action Rest Periods Load and Volume Repetition Velocity Exercise Selection Frequency and Order Muscle Action • Dynamic repetitions of concentric (CON) and eccentric (ECC) actions; • Isometric actions serve stabilizing role; • Concentric actions elicit greater growth hormone response; • Training should include both CON and ECC. Loading and Volume • Load: amount of weight - key variable – Determined by RM or % of 1RM – Increase by 2-10% when can perform load for 1-2 reps over desired # reps – Maximal strength gained with 12RM in untrained and 8RM in trained • Volume: total work performed Number of Sets • Multiple set programs and periodized multiple set programs are superior to single set programs over both short and long term periods for strength; • 3 sets better than 6 and 12 sets; • Altering frequency, intensity and volume best strategy to improve strength. Galvao DA et al. J Strength Cond Res. 2004 Aug;18(3):660-667. Volume of Training Sets x Repetitions x Resistance Sets Reps Weight Volume 3 5 87 1,305 3 10 80 2,400 2 15 70 2,100 1 60 30 1,800 Impulse Product of force applied and time during which it acts: Impulse = Force x Time of application Impulse Force Time Exercise Selection and Order • Single Joint (leg extension, biceps curl) - less risk because requires less skill • Multiple Joint: more neurally demanding and more effective for overall strength • Order - from large to small muscle mass/groups Rest Periods • Dependent on – Training goal – Relative load lifted – Status of individual • Primary determinant of intensity • Affects metabolic and hormonal demands • Determines amount of ATP-CR resynthesis Repetition Velocity • Not adequate research but: • “Gold Standard” = 2:1:4 or 2 s CON; 1 s pause; 4 s ECC • Slow: 2:4 ( good for novices) • Super Slow: 10:5 • Moderate: 2:2 • Fast: 1:1 Frequency • Function of type of training session, training status, and recovery of person • Typical: 2 -3 d/wk to allow for recuperation • Maintenance: 2 d/wk • Competitive Lifters: 5 - 7 d/wk Specific Training Outcomes Muscle Muscle Maximal Power Endurance Hypertrophy Strength ECC:CON ECC:ISO:CON ECC:ISO:CON ECC:CON 1-3 Sets 4-6 sets 3-5 sets 3-5 sets 15-20RM 8-15RM 3-8RM 1-3RM 30-60s rest 1-2m rest 3-5m rest 5-8m rest 1:0:1 2:1:2 1:1:1 Explosive 2-3x/wk 3-5d/wk 3-5d/wk 4-6d/wk Sept Develop Strength Oct Nov Dec Muscle Endurance Jan Feb Develop Strength Mar Apr Muscle Endurance May Periodization Plan Jun Jul Cross Training/Rest Aug Develop Strength Approximate Intensity Levels Relative to a 1RM Number of Energy % of 1RM Reps System > 95 1 ATP/CP 80 - 95 2-5 ATP/CP 65 - 80 6 - 10 ATP/CP/LA 50 - 65 8 - 15 ATP/CP/LA 30 - 50 15 - 60 LA/Aerobic Optimal Strength Gains • Maximal strength gains elicited with training intensity of 85% of 1RM (2 - 5 reps), 2 d/wk, with 8 sets per muscle group. – Peterson MD et al. J Strength Cond Res. 2004 May;18(2):377-382. Optimal Power Gains • Optimal load for maximal power gains depends on nature of exercise (single versus multiple joint exercises) and experience of athlete: – Untrained load 30-45% of 1RM – Trained load 40 - 70% of 1 RM • Explosive training best • Periodization important Kawamori N et al. J Strength Cond Res. 2004;18(3):675-84. Eccentric Loading • Supra maximal loading to optimize force production – E.g. loads set at 100, 130 and 150% of 1RM • May be useful for recruiting high threshold motor units. Safety of Strength Training • Relative Safety of Weightlifting and Weight Training. Hamill 1994. – Injury rates were 0.0012 per 100 hours of participation compared to 0.03 for basketball, 0.1 for football, and 0.03 for all other athletics. • Regular participation in broad-based training that includes strength training can significantly lower sports-related injury rates and time for rehab of adolescents. Faifenbaum 2004. Physical Performance and Injury Prevention Model 8 Primary Exercises 1. Leg Press or Parallel Squat 6 2. Bench Press or Incline Bench 4 6 3. Lat Pulldown or Low Pull 3 2 4. Shoulder Press or Upright Row 7 7 Secondary Exercises 1 5 5. Leg Curl and Leg Extension 6. Biceps Curl and Triceps Extension 5 7. Low Back Extension and Abs Crunch 8. Grip/Forearm and Calves 8 Contribution of Strength to Performance of Tasks Milwaukee PAT Roof Ladder Relatve Contributions (N-22) Relatve Contributions (N-467) 23.9% 5.9% 14.4% 39.7% Size 45.9% 70.2% Strengt Combat Testｨ h "Elite Firefighter" Relative Contributions (N-22) Relatve Contributions (N-174) Fitness 16.0% 30.6% 26.6% 28.6% 40.8% 57.4% ACSM Position Stand • To develop and maintain cardiorespiratory and muscular fitness, and flexibility in healthy adults – 8–12 repetitions for 8–10 exercises, including one exercise for all major muscle groups; – 10–15 repetitions for older and more frail persons. Summary: Strength Training • Is a physiologic stimulus with multiple actions; • Is complex and requires administrative and physiologic planning; • Confers benefits to young and old, weak and strong; • Is safe when entered into with clearly defined goals; • Requires an understanding to be effective. Questions ?
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