MEDI221 Mechanical Ergometry PDF

MEDI221 Mechanical Ergometry  Text Book Chapter 5 (Page 121+) Lecture Outcomes Describe the terms Force, Work & Power Calculate force, work and power from provided parameters Describe methods of ergometry and their application Describe what...

MEDI221 Mechanical Ergometry  Text Book Chapter 5 (Page 121+) Lecture Outcomes Describe the terms Force, Work & Power Calculate force, work and power from provided parameters Describe methods of ergometry and their application Describe what is meant by specificity and reliability of tests Describe limitations of different methods  What is Ergometry? Ergometry: The measurement of mechanical energy production. Force- the resistance to overcome Work- the amount of exercise Power- the intensity of exercise Ergometer: A device from which work and power can be determined. Many types- swim, step, run, cycle, row, kayak, ski etc. Validity (inc. specificity) Your Turn Which of the two Need to consider: bikes explained would be used to 1. What it is you are trying to assess? Anaerobic and aerobic power? measure VO2max Performance or fitness? and why? 2. Does the ergometer measure what you want it to? Muscle groups, velocities, exercise patterns, intensities Power: average, peak, rate of force development etc. Reproducibility- reliability also really important to consider  Work is the energy imparted onto an object when it is moved to a position of higher potential energy. This lecture only focuses on Mechanical Energy = Capacity to Energy Perform Work Work Work = Force X Distance [N.m, = Joule (J)] Force = Mass X Acceleration Therefore, Work = Mass X Acceleration X Displacement Power Power is the rate at which work is/can be done or performed Power= Work/Time [J.s-1, Watts] Your Turn How would you calculate the force of each of these hits? Watch: https://www.youtube.com/watch?v=av9jrlJUJQE  Who has the most force? Scenario 1: a=3m/s/s a=4m/s/s m=80kg OR m=80kg F=ma F=ma F=80kg X 3m/s/s F= 240N  F=80kg X 4m/s/s F= 320N  Who has the most force? Scenario 2: a=3m/s/s a=4m/s/s OR m=130kg m=80kg F=ma F=ma  F=130kg X 3m/s/s F= 390N F=80kg X 4m/s/s F= 320N If you (weighing 90kg) wanted to overcome the 220N force Your Turn: produced by a 100kg rugby Example Exam player how fast would you Question (Show Working) need to be running? Acceleration Can mean different things in different sports Gravity (e.g., climbing, jumping, throwing) Your body (e.g., springing, jumping) Someone else’s body weight (e.g., tackling Sporting equipment (e.g. ball, javelin, racket) Gravity= 9.8 m/s/s These calculations are important for labs and exams Of Interest- Work and Power in Rugby https://physicsinrugby2 012.weebly.com/energy -work-and-power.html  Always a Q like this in Calculation “The Bench Step” your exam The mechanical work is in raising (lifting) the body. Typically work is varied by altering the cadence (i.e. faster cadence greater mechanical work): Q. Calculate Work: 60 kg female, 30 steps/min for 20 mins @ 0.20 m step height. Work = force x distance = mass x gravity (m·s-2) x height (m) x cadence (·s-1) x duration (s) = 60 kg x 9.8 m·s-2 x 0.20 m x 0.5 ·s-1 x 1200 s = 588N x 120 m = 70 560 J Remember you make Power = Work/Time sure of your units. = 70 560/1200 s = 60 J ·s-1 Watts  Text Book: McArdle, Katch & Katch Know how to calculate work on a treadmill, cycle, bench press etc….. Different Ergometers Used in Exercise Physiology Monarch Cycle Ergometer Friction (Mechanically) braked ergometer Apply a known mechanical resistance against a flywheel As cadence increases so does work Pros: easy to use, calibrate and calculate, cheapish and relatively robust Cons: Limited precision of work rate control, reducing reliability To keep a set wattage they must maintain the same cadence  Pro’s: highly specific, encourage central v’s peripheral fatigue Cons: Cost/size, variability in running Treadmill efficiency (therefore less reliable in energy cost unless measured) Usually motorised Incline slope or Attached to a load cell to measure work Work = Force x Displacement = body mass x gravity x vertical velocity x time If slope is known: = body mass x gravity x %grade x distance run If angle known: = body mass x gravity x sin x distance Calculate the work done on the treadmill. W=FxD W = force x vertical distance travelled (if known) OR W = force x sin θ x speed x exercise duration (if angle of treadmill from ground is known) Q. Calculate Work: 50 kg female, 5km/hr, incline of 8o for 1 hr Work = Force x Displacement = 50kg x sin8O x 5000m/hr x 1 hr = 34 800kg/m (note: make sure your units for time are the same) Power = 34 800kg-m / 60mins = 580 kg-m per min More Modern Ergometers Ergometry Summary Many applications for ergometry Many different approaches- depends on what you are measuring and how accurate you need it to be Consider: Validity Does it produce the desired stress Does it measure what you want Reliability How reproducible is the stress Practicality Cost, portability, ruggedness, safety etc.