2 Muscular StrengthDefinition: The ability of a muscle group to develop maximal contractile force against a resistance in a single contraction.Force developed during muscular contraction is determined by velocity of the contraction.Maximal force is determined at a velocity of zero. Maximal force is produced when the limb is not rotating. As the speed of joint rotation increases, the muscular force decreases.
3 Muscular EnduranceDefinition: The ability of a muscle group to exert submaximal force for extended time periods.Similar to muscular strength, it can be assessed for static (isometric) or dynamic contractions.
4 Types of ContractionsBoth strength and muscular endurance can be assessed for static and dynamic muscular contractions.Static (isometric) contractions: no visible change in joint angleDynamic: visible change in joint angleTypes of dynamic contractionsConcentricEccentricIsokinetic
5 Concentric Contraction Force exerted by muscle or muscle group exceeds external resistance or load.Joint angle decreasesMuscle shortens
6 Eccentric Contraction Joint angle increasesMuscle lengthens while contractingServes as a braking mechanism to decelerate body segment movement, or to resist gravity.
7 Isokinetic Contraction Maximal contraction of muscle or muscle group at a constant velocity throughout entire range of motion (ROM).Specialized machines control velocity of contraction and adjust external resistance to match the force produced at degree in the ROM.Resistance is variable, velocity is constant)(Electromechanical devices vary the resistance to match the muscular force produced at each point in the ROM. Thus, isokinetic exercise machines allow the muscle group to encounter variable but maximal resistances during the movement.)
8 “Isotonic Contractions” Both concentric and eccentric contractions are sometimes called isotonic (“iso,” same; “tonic,” tension). The term “isotonic contraction” is a misnomer because the tension produced by the muscle group fluctuates greatly even though the resistance is constant throughout the range of motion (ROM).Thus, the greatest resistance that can be used during regular, dynamic exercise is equal to the maximum weight that can be moved at the weakest point in the ROM.
9 Figure 6.2The fluctuation in muscular force during isotonic contractions is due to the change in muscle length and angle of pull as the bony lever is moved, creating a strength curve that is unique for each muscle group. For example, the strength of the knee flexors is maximal at 160° to 170°.
10 Assessing Strength and Endurance Measures of static or dynamic strength and endurance are used to establish baseline values before training, monitor progress during training, and assess the overall effectiveness of resistance training and exercise rehabilitation programs(continued)
11 Assessing Strength and Endurance Isometric strength is measured as the maximum force exerted in a single contraction against an immovable resistance (i.e., maximum voluntary isometric contraction, or MVIC in kg or N).Devices used to assess static strength and endurance: (see photos in text)Isometric DynamometersCable tensiometersStrain gaugesLoad cellsHandheld Dynamometers(continued)
12 Assessing Strength and Endurance Hand grip dynamometry for strength:Adjust hand grip to accommodate client’s hand.Set dial to zero.Stand upright and grasp dynamometer.Arm position varies between protocol selected.Client squeezes hand grip quickly and as tightly as possible and then releases the pressure.Extraneous body motion is kept to a minimum.Do 3 trials for each hand; 1-minute rest between trials.Select best trial for each hand.
13 Back and Leg Dynamometry Both use same dynamometer; score in kgFor leg assessment:Using the back and leg dynamometer, the individual stands on the platform with trunk erectStart with knees flexed to 130o to 140o.Use pronated grip with bar across thighs.Extend knees but do not engage back muscles to pull bar straight up.For back assessment:Fully extend knees and keep head and back erect.Use over-under grip with the bar across the thighs.Pull bar straight up by rolling shoulders without bending backward.
14 Dynamometry Normative Values Can use dynamometric scores to determine static muscular strength:Add best strength score for right hand, left hand, legs, and back.Be sure to convert values to lb.Can use total dynamometric score to compute relative static muscular strength score (divide total score by body weight and multiply by 100).See Tables Next Slides
17 Assessing Strength and Endurance (continued) Dynamic Muscle Testing: strength measured as the maximum force exerted in a single contraction against a movable resistanceDevices used to assess dynamic strength and endurance:Free weightsConstant-resistance machinesVariable-resistance machinesIsokinetic machines(continued)
18 Isometric Strength Assessment Guidelines Use cable tensiometers or strain gauges.Follow standardized procedures closely.Select proper tensiometer based on anticipated strength score (above or below 100 lb).Isometric assessments specific for single joint angle.Testing of multiple muscle groups is recommended for overall strength score.Digital, handheld dynamometers are now available.Detailed procedures for digital dynamometry are in appendix C of textbook.
19 Isometric Strength Assessment Guidelines (cont.) Digital, handheld dynamometers are now available.Detailed procedures for digital dynamometry are in Appendix C of textbook.
20 Dynamic Strength and Endurance Constant-resistance machines or free weights are best.However, each only assesses maximal strength of weakest point in joint ROM.Why? Mechanical and physiological advantage changes throughout ROM, but resistance doesn’t.Variable-resistance machines (VRM) were created to address this (i.e., lever, cam, or pulley).Load changes throughout ROM with VRMs, so it is difficult to assess maximal strength. As the weight is lifted, the mechanical advantage of the machine decreases.Variable-resistance exercise machines, therefore, have limited usefulness for maximal testing - Not recommended for strength assessment, but good for resistance training programs.
21 Free weights Versus Constant-Resistance Machines Increase, and require more neuromuscular coordinationAllow full ROMSpotter may be requiredIncrease neuromuscular coordinationROM limited by machineNo spotter requiredWeight increments may be limitedMachines may not accommodate all body types
22 Free-Motion MachinesEliminate many challenges of free weights and constant-resistance machinesAllow movement in multiple planesCan allow both constant- and variable-resistance exerciseHave many adjustable compartmentsMust simulate starting and ending body position of validated muscular tests in order to use those normative valuesNote settings during baseline assessment testing; use them for follow-up assessment settings.
23 Dynamic Strength Testing One-repetition maximum (1RM): maximum weight that can be lifted for one complete repetition of the movementInvolves trial and error in setting weightsHas been applied to all age groups, but use standardized technique to keep all clients safe.Spotting for your client is a must.1RM bench press and leg press are good for assessing upper body and lower body strength.Compute relative strength (maximal lift/body mass) and use normative values. Norms for men and women are provided in Tables 6.4 and 6.5.
24 Dynamic Strength Testing 1 RM max testing 1. Have your client warm up by completing 5 to 10 repetitions of the exercise at 40% to 60% of the estimated 1-RM.2. During a 1 min rest, have the client stretch the muscle group. This is followed by three to five repetitions of the exercise at 60% to 80% of the estimated 1-RM.3. Increase the weight conservatively, and have the client attempt the 1-RM lift. If the lift is successful, the client should rest 3 to 5 min before attempting the next weight increment. Follow this procedure until the client fails to complete the lift. The 1-RM typically is achieved within three to five trials.4. Record the 1-RM value as the maximum weight lifted for the last successful trial. The following basic steps are recommended for 1-RM testing.
25 Dynamic Endurance Testing Dynamic Muscle Endurance TestsPerform multiple repetitions with weight that is set submaximal load (%1RM) or set %body mass.Individual should be able to perform 12 to 15 reps of each exercise with weight that is 70% of 1RM.The YMCA (Golding 2000) and ACSM (2010) recommend using a bench press test to assess dynamic muscular endurance of the upper body.For this absolute endurance test, use a flat bench and barbell. The client performs as many repetitions as possible at a set cadence of 30 repetitions per minute.(continued)
26 Dynamic Endurance Testing (continued) Other optionsSeven-item multiple repetition battery: maximum of 15 reps at set % of client’s body mass; add the number of reps completed over the seven items; use sum for overall categorization of dynamic muscular endurance scoreTable 6.8 provides percentages for each test item, as well as the scoring system and norms for college-age men and women.
27 Isokinetic Assessment Dynamic Muscle Testing using Isokinetic and Omnikinetic Exercise ModesIsokinetic dynamometers assesses strength, endurance, and power.Machine generates resistance equivalent to client’s muscular force generation (accommodating resistance).Limb moves at constant, preselected velocity.Can evaluate peak torque, total work, and total power for each muscle group tested.
28 Omnikinetic Assessment This testing system provides an accommodating resistance that adjusts to both the force and velocity output of the individual and is not limited to a preset velocity of limb movement.Force and velocity adjust downward as client begins to fatigue (self-accommodating)Assesses isokinetic strength and endurance of both fast-twitch and slow-twitch motor units in the muscle group.
29 Field Test Assessments In certain field situations, you may not have access to dynamometers, free weights, or exercise machines to assess muscular fitness. As an alternative, you may use calisthenic-type strength and endurance tests to assess your client’s strength and muscular endurance.Dynamic strength tests: Add additional weight to client and have them perform the desired movement as a 1RM.Dynamic endurance tests: maximum number of reps performed for select calisthenic exercisesPull-upsPush-ups (see Table 6.10 for Norms)Trunk curls (Table 6.11 for Norms)
30 Sources of ErrorPossible reasons for measurement errors in fitness testing:Client factorsEquipmentTechnician skillEnvironment
31 Sources of ErrorClient factors - Clients with limited or no prior weightlifting experience need time to practice each lift to control for the effects of learning on performance.Clients should get adequate sleep before performing these tests, and you should restrict the use of drugs and medications that may adversely affect their performanceMotivating clients and rest between lifts are important.
32 Sources of ErrorEquipment – The equipment used for testing must match the equipment used to develop the strength norms of the test.It is also important to calibrate the equipment and make sure that it is in proper working condition prior to testing.When selecting exercise machines, make sure that the equipment can be properly adjusted to accommodate varying limb lengths and body sizes.
33 Sources of ErrorTechnician skill - All strength testing should be done by qualified, trained technicians who are knowledgeable about proper lifting and spotting techniques and familiar with standardized testing procedures.Explain and demonstrate the proper lifting technique and then correct any performance errors you see as the client practices.
34 Sources of ErrorEnvironment - The room temperature should be 70° to 74° F (21° to 23° C) to maximize subject comfort during testing.Use a quiet, clean environment with limited distractions (not an overcrowded weight room, for example).Remember to pretest and posttest your client at the same time of day to control for diurnal variations in strength.
35 Additional Concepts Can estimate 1RM from submaximal tests. Although 1-RM tests can be safely administered to clients of all ages, sometimes it is preferable to estimate the 1-RM.The 1-RM may be underestimated for clients with little or no exercise experience because they are unaccustomed to or may be apprehensive about lifting heavy loads.You can estimate the 1-RM of your clients from submaximal muscle endurance tests (see pg. 144)
36 Additional ConceptsLook for muscle balance. Muscle imbalance may compromise joint stability and increase the risk of musculoskeletal injuryMuscle balance ratios differ among muscle groups and are affected by the force-velocity of muscle groups at specific joints.To control limb velocity during muscle balance testing, you will do best to use isokinetic dynamometers. (see chart on pg )The difference in strength between contralateral (right vs. left sides) muscle groups should be no more than 10% to 15%, and the strength-to-body mass (BM) ratio of the upper body (bench press 1-RM/BM) should be at least 40% to 60% of the lower body relative strength (leg press 1-RM/BM)
37 Additional ConceptsBest to express client strength results in relative terms.Because strength directly relates to the body mass and lean body mass of the individual, you should express the test results in relative terms (e.g., 1- RM/BM).This is especially true in comparing your client’s score to group norms and in comparing groups or individuals differing in body size and composition (e.g., men vs. women or older vs. younger adults).If you compare the client’s relative strength scores (from pre- and posttest training), you will be able to evaluate the change in strength that is independent of a change in body weight.
38 Working With Older Clients Muscular strength and endurance are important for maintaining functional independence and activities of daily living (ADLs).You can use 1RM assessments with this age group.You may prefer to estimate 1RM from submaximal loads:Brzycki (1993) equation and Wathen (1994) equation are recommended (see pg. 146)
39 Functional Testing for Older Clients Rikli and Jones (2001) battery assesses physical capacity and functional fitness through 2 tests:30-second chair stand30-second biceps curlsThese tests have functional application for older clients’ ADLs.Be sure to follow standardized technique and follow known safety precautions. (see demos, instructions, and norms pgs )
40 Working With Children Children can safely perform 1RM trials. Must be closely supervisedBest results obtained using child-sized equipmentNo support for contention of premature closure of epiphyseal plates due to strength trainingFollow standard guidelines when testing 1RM:Be sure to allow for familiarization trial(s)Focus on proper lifting and breathing techniquesSee Testing Protocol, (p.150)