Isokinetics in Rehabilitation Isokinetic Exercise Hislop

Isokinetics in Rehabilitation

Isokinetic Exercise Hislop & Perrine (1967) — movement that occurs at a constant angular velocity with accommodating resistance max muscle tension can be generated because resistance is variable to match the muscle tension produced at various points in the ROM!

Isotonic vs. Isokinetic Exercise

Advantages 1) isolate weak muscle groups 2) work maximally throughout ROM 3) velocities simulate functional activity? 4) inherent safety mechanism

Disadvantages 1) cost 2) open-chain motions 3) cardinal planes

Terminology 1) 1) force — when a stimulated muscle acts against a resistance force is produced 2) 2) torque — F x D (from fulcrum or axis of rotation) 3) 3) work — applied force times distance of rotation 4) 4) power — time required to perform work

Normal Torque Curve 1) 1) Angle Specific Torque (AST) — — 2) 2) Peak Torque (PT) — — 3) 3) Average Torque (AT) — torque over entire ROM — lower than PT, higher reliability

Isokinetic Curves

Isokinetic Curves

Power Curves

Abnormal Torque Curve Predicting Injury from Curve? can look at pt of pain, but not predict injury! non-volitional reproduction of pain at the same pt in ROM isokinetics will accommodate the pain by decreasing the dynamometer force

Types of Dynamometers Passive — primary function is the dissipation of energy torque produced by the pt driving the dynamometer old Cybex systems Active — “robotics”, can either dissipate energy by the patient or supply energy to do work on the patient Kin Com, Biodex, Cybex

Instrumentation Mode of Muscle Action con/ecc isometric passive Test Velocity 00 /s — 1000 /s /s above 300 /s /s difficulty generating force (not isokinetics!!)

Principles of Isokinetic Strength Assessment 1) 1) Musculoskeletal and CV. Screening 2) 2) Pt. Education/Familiarization 3) 3) Stabilization/Joint Alignment 4) 4) Gravity Correction 5) 5) Test Velocity

Gravity Correction Must be performed during any gravity dependent joint testing position GC value + to force ? GC value (-) to force ? some dynamometers perform this either dynamically or stationary Failure to GC results in: quads under predicted hams over predicted

Confounding Factors to Accurate Isokinetic Evaluation Assess strength not PAIN! Joint effusion (neuro-inhibitory effect) Muscle co-activation (hams contract near terminal ROM with knee extension may effect AT!)

Test Protocols 1) 1) interrupted — test repetitions separated by a time period greater reliability 2) 2) continuous — no pause between test repetitions better predictor of PT (peak torque) 3) 3) sequencing — con/con, con/ecc, ecc/ecc, ecc/con

Interpreting an Isokinetic Evaluation 1) 1) Torque, Power, Work — — — all have high r values — AT more reflective of pt’s capability to to generate force thru ROM 2) 2) Muscle Endurance — — 3) 3) F-V Relationships — — — differences con vs. ecc

Factors affecting muscular force generation Force-velocity relationship concentric

Factors affecting muscular force generation Force-velocity relationship Concentric/eccentri cc

F-V R Curve – Knee Flex & Ext

FV-R Ankle Eversion

Interpreting an Isokinetic Evaluation Force/Torque ratios Relative to BW — — Nm torque/kg BW mainly involving the lower extremity Bilateral Muscle Group Comparisons Reciprocal Muscle Group Comparisons Knee flex/ext (H: Q) =. 67 ratio Shoulder ER/IR =. 70 -. 90 (. 65 M &. 80 F)F) Shoulder ABD/ADD = (1. 0 M & 2. 0 F)F) Ankle E/I Ratios =. 65 -.

E (CON) : I (ECC) Ratios in the Ankle Trend is for ratios to be < 1. 0 why? ECC strength values in the denominator will in most cases be greater than the CON values found in the numerator 40% greater force production ECC less CON force generated at the higher velocity (120°/sec) lowers the ratios at the higher speeds Lack of normative values for comparisons

E (ECC) : I (CON) Ratios in the Ankle Trend is for ratios to be > 1. 0 why? ECC strength values in the numerator will in most cases be greater than the CON values found in the denominator 40% greater force production ECC Interesting to note that at the higher velocity (120°/sec) that the ratios are elevated ECC force production in the ankle typically rises from the slower velocities to peak around 120°/sec

Implications Normative values are needed to allow for meaningful comparisons Will prove useful for clinician: rehab goals return to play guidelines Perrin (1993) suggests the use of CON to ECC ratios “traditional” Hertel (2000 — Sports Med) suggests ECC eversion to CON inversion ““ Functional” ratio Aagaard et al. (1998 — Am J Sp Med)

Isokinetic Strength Discrepancies

H: Q Ratio Comparison between Athletic Groups

Physiological and Neuromuscular Effects of Isokinetic Exercise Glycolytic, ATP-PC, Krebs Cycle Enhancement Motor Unit Recruitment Duration of Exercise determined by time instead of reps!

Velocity Spectrum Exercise Theories Supporting Usage: 1) 1) Type I (Slow Twitch) Fibers activated at lower velocities longer twitch contraction times specialized for use at slow velocities 2) 2) Type II (Fast Twitch) Fibers specialized for high power/high velocity/short duration 3) 3) Selective Fiber Recruitment vs Variations in the Order of Motor Unit Recruitment

Specificity of Training Con vs. Ecc? most activities are a combination of both Strength Overflow? high velocity training is “less specific” than low velocity Submaximal Isokinetic Exercise if it’s submax then not isokinetics!!

Understanding Eccentric Muscle Actions: Implications for the Clinician

““ ECCENTRIC” a person who has an unusual, peculiar, or odd personality, set of beliefs, or behavior pattern.

Isometric Muscle Actions Muscle creates tension without a change in length Max force is created at the end of the ROM (review length-tension relationships) Peak force = MVC (Maximal Voluntary Contraction) strength of the muscle without any external load

Length-Tension Relationships

Concentric vs. Eccentric Muscle Actions Concentric the muscle develops tension while shortening review sliding-filament theory Eccentric the muscle develops tension while lengthening review physiology of eccentric muscle actions

Sliding-Filament Theory Revisited Resting state = lengthened position Contracts = shortens (concentric) Muscle filaments are pulled back creating new molecular attachments actin and myosin bonds ratcheting effect requires a tremendous amount of energy (ATP)

Physiology of Eccentric Muscle Actions Review articles by H. E. Huxley (Science, 1969) and W. T. Stauber (Exercise and Sport Sciences Reviews, 1989) Contractile and elastic components of the muscle are active Force required to break the cross-bridges within the sarcomere is greater No recycling of bonds (remain in high energy state)

Force Production Differences between Eccentric and Concentric Muscle Actions Differences associated with muscle physiology 40% greater force production require less energy Force-velocity relationships traditional curves contemporary viewpoint

Types of Resistance Training Isometric muscle produces tension without changing length Isotonic muscle produces tension while changing length fixed resistance & variable speed Isokinetic muscle produces tension while changing length variable resistance & fixed speed

Advantages and Disadvantages of the Various Types of Resistance Training Isometrics Isotonics free weights variable resistance machines Isokinetic dynamometers (Biodex® & Cybex®)

Why are Eccentric Muscle Actions Important? Walking: ““ falling forward” interrupted by heel strike (knee flexed — quads act eccentrically) stance phase — tibia begins to roll-over the foot (gastrocnemius fires eccentrically) only concentric action during walking is psoas firing to flex the hip

Why are Eccentric Muscle Actions Important? Running: the activity represents “stretch and recoil” ““ toe strike” quads absorb elastic energy which is then released to contribute to forward momentum ““ deceleration phase” hamstrings act eccentrically to slow the lower leg deficient strength = strain injury ““ foot plant” hamstrings reduce forward translation of the tibia (unload the ACL)

Why are Eccentric Muscle Actions Important? Throwing Activities: baseball throw involves 88% eccentric actions IROT’s are acting eccentrically during the wind-up (“cocking phase”) energy recaptured by the “stretch and recoil” mechanism = forward momentum of ball on “follow-through” EROT’s act eccentrically to slow the arm down after release

Why are Eccentric Muscle Actions Important? Jumping Activities: best example of “stretch-recoil” mechanism (Stretch-Shortening Cycle / Plyometrics) quads and calf (gastroc-soleus) act eccentrically at “foot plant” to store energy that is released at take-off box jumps, depth-jumps, plyo’s

Clinical Implications Muscle Strength Training Isometric angle specific gains Isotonic concentric eccentric Limiting factors with contemporary variable resistance devices Research studies indicating eccentric strength gains are the greatest

Clinical Implications Muscle Strain Injuries: M-T junction Eccentric muscle actions can occur early in rehab because stretch receptors are de-activated process called concentric “off-loading” used in patellar and Achilles tendinitis, strains, rotator cuff pathologies

Clinical Implications Eccentric “over-loading” used with muscles that statically contract to stabilize a joint (shoulder, knee, etc…) stabilizing muscles counteract the tendency for the unstable joint to sublux used in the prevention of recurrent MT injuries use concept of progressive resistance exercise (PRE’s) MT unit is then exposed to functional levels of resistance

Negator™ Research The Negator™ offers enhanced eccentric isotonic exercise in a safe, controlled manner Can attach to existing variable resistance machines No need for assistance by other strength professionals

1 RM Percentage Gain

Negator™ attached to a Cybex Arm Curl Device

Negator™ attached to a Cybex Arm Curl Device

Negator™ Counter-Weight Stack

Negator on Leg Curl Device

Video of the Negator

Discussion How are you interpreting an isokinetic evaluation on muscle endurance by performing multiple repetitions of contractions. How do you conduct a isokinetic test to determine the proportion of fast-twitch muscle fiber for a young sprinter. What is the importance of isokinetic eccentric contraction test to athletes prone to sport injury.