1. 1 Strength Testing: variability and relevance Readings - Matheson - Effects of instructions on isokinetic trunk strength variability, reliability absolute value and predictive value Garg - A comparison of isokinetic lifting strength Wolf - relationships among grip strength work capacity and recovery OUTLINE Summaries of above findings and discussions Complete knowledge of methods and results not required

2. 2 Psychological Factors Classic experiments - arm strength –normal conditions –immediately after loud noise –while subject was screaming loudly –influence of alcohol and amphetamines –hypnosis observed increased strength - most with hypnosis theorized temporary modification in CNS - argued most people - neural inhibition (protective reflex) reduced inhibition –highly trained athletes –arousal - unexplainable feats –early phase of strength training

3. 3 Effect of Instructions: ( Matheson) Previous discussions emphasized the need for standardized protocol –consistent instructions important Matheson paper supports this tenet –asks - what type of instructions produce the best results? –Optimize reliability, validity Hypotheses high demand instruction in isokinetic strength testing will show; –decreased variability –increased peak torque –produce stronger correlation with performance capacity When compared to uniform instructions asking subject to put in a consistent effort

4. 4 Instructions - Discussion With high demand instructions Hypothesis one performance variability –Tables 2 and 3 - % coefficient of variation - four trials each speed –Lower variability with high demand less variability at slower speeds with both types of instruction Hypothesis two peak torque - fig 1,2 tables 4 and 5 –higher in high instruction group –groups affected similarly by changes in velocity Hypothesis three Predictive ability - table 6 through 9 –significant correlation between isokinetic strength and lifting capacity in progressive test Only with high demand instruction

5. 5 Comparing Isokinetic Strength (Garg) Goal of research –determine effects of speed of lifting and box size on isokinetic strength –compare isokinetic with static lifting strength psychophysically determined maximal acceptable weight (MAW) Relevance of Research –Measurement of human strength is important for job design –Important to match physical strength requirements with worker capabilities to prevent injury –Measurement of dynamic strength is complex –Isokinetic strength is commonly used to measure dynamic strength –The use of boxes instead of a bar is a better simulation of actual lifting tasks

6. 6 Methods 9 male college students - range in age 22-36 (table 1) 12 lifts per hour (every 5 minutes) lift floor to bench (.8 m) 3 box sizes 25 - 50 cm wide open technique - subjects choice ** Measure MAW, static strength, isokinetic strength –MAW - adjust weight till comfortable –Static measured at origin of lift –Isokinetic evaluated at 3 speeds RPE on low back for all lifts

7. 7 Results Progressive decline in mean and peak isokinetic strength –with inc speed and inc box width –Fig 1 and 2 –speed had greater impact than width Recommend lifting slowly However, high speed lifting perceived to be less stressful –RPE 10.7 (fast) vs 12.7 (slow) –Fig 3 static strength and MAW higher correlation with mean than peak isokinetic strength –high speed - mean isokinetic - within 6% of MAW –low speed - mean - equal to mean static strength –Fig 4

8. 8 Recommendations recommend –both speed of lifting and box width should be controlled carefully –using MAW and Static strength testing SST results in higher allowable limits for workers MAW - effectiveness not yet as well documented the complexities of isokinetic strength testing and its relationship to safe lifting capability are not fully understood

9. 9 Grip Strength, Work Capacity and Recovery Wolf Relationships between strength, fatigue and work capacity are central to occupational rehabilitation Musculoskeletal impairments are often expressed as loss of strength –% disability strength and endurance correlation exceeds.90 –endurance tests often assess repetitions to failure using a % of body weight –strength test often use one rep max (isotonic) ; not always appropriate 1 RM= (weight) / [1- (RM *.02)]

10. 10 Grip Strength, Work Capacity and Recovery questions in paper –how important is strength as a component of work capacity? –how do work capacity and strength affect recovery time? Relevant research Capacity to sustain work activity is inversely related to power required –exponential decrease in endurance, as demand approaches max –Walsh (Fig 1 and 2) after injury - loss of power leads to loss of capacity –rest from injury - often increases impact due to muscular de-conditioning

11. 11 Background Rehabilitation –strengthen and condition worker to improve capacity –Various programs (functional restoration, work conditioning, work hardening) –Often difficult to establish and define dose of intervention precisely The goal is to accelerate the rate of rehab and shorten treatment time Physical training goals in the workplace are different from those ot athletes –Athlete: improve capacity to enhance performance –Worker: improve capacity to minimize the risk of injury and reduce the strain of performing tasks

12. 12 Background Prediction equations for muscular endurance at a given % of max contraction - constants for each muscle group (Sato) –results 10-35 % decline in strength –longer bout, lower recovery strength Fatigue - theory –short - high intensity exercise - metabolic inhibition –longer duration - fatigue may be at level of E-C coupling - ? K+ ? Relevance of isometric evaluation –low - due to low prevalence of isometric activity –Greater relevance for hand

13. 13 Relationships Research goals of Wolf study –develop technology necessary to support a treatment strategy –dose of exercise is able to be closely tied to expected levels of recovery Address issues of ; –expected work duration –work capacity –and recovery rates for sustained high output work tasks Methods - 40 healthy subjects - 1/2 male –Standard body position and instructions –repetitive gripping task at set pace –Measure pre trial isometric max –Utilize 25, 50 and 75 % of max –1 sec reps until fatigue - 2 min recovery –measure isometric grip strength 1, 5 10 and 20 min of recovery –average of three trials

14. 14 Methods (continued) evaluate isotonic strength –LIDO - isotonic - progressive protocol –complete ROM in less than 1 sec –inc resistance - repeat to fatigue Test - based on isotonic results –repetitive gripping to fatigue – 75% and 50% of isotonic max –then 25% for twice as long as 50%

15. 15 Results correlation isometric / isotonic strength no correlation between isometric or isotonic strength and duration of work at either 75 or 50 % significant relationships between isotonic strength and work capacity at 75 and 50% levels Isotonic strength best predictor of work capacity at 75 % level - –When compared with duration Work duration and isotonic strength had a similar predictive ability at the 50% resistance

16. 16 Recovery Results No significant gender differences –either recovery time or % at time points –table III and fig 1 Recovery rate and time to recovery –subjects categorized - time to 100% –significant differences in degree of recovery Fig 2 –no differences in rate –similar slope, different starting points - –Related to degree of loss of strength Good predictor of length of recovery Standards - avg 20% decline in strength with protocol - 20 min recovery –variation - abnormal - intervention –standards - tables 4 and 5

17. 17 Conclusions on Types of Strength testing High demand instructions(isokin) –Reduce variability with high demand instructions –higher correlation to isotonic –good predictive ability for lifting capacity Isokinetic testing –correlations depend on lifting speed and box width –difficult to establish safe lifting capacity –Difficult to design - many variables –Better to use static strength and MAW

18. 18 Conclusions on Types of Strength testing Recovery from fatigue - FCA –duration of work difficult to correlate to either isotonic or isometric strength –work capacity correlates better to isotonic strength than isometric –recovery rates similar between genders and degree of strength loss useful in diagnosis - hand grip only from this study

19. 19 General Conclusions The goals of physical training program in the workplace are Improve a workers physical capacity Minimize risk of injury Reduce the strain of performing daily tasks The lack of physical fitness is a contributing factor for musculoskeletal injuries at work The logistics of implementing changes in a workplace to reduce strain must be considered Using a bar is inappropriate for manual materials handling assessments The type of strength assessed will have a significant impact on the design of weight limits for job design Results from strength tests are influenced by the subjects motivation and perception of how much force to generate without getting injured