Standard Operating Procedure Equipment / Procedure:
Cycle Ergometry – Monark Ergometers
Assessor’s name & date: Reviewer’s name & date: Review Date:
Richard Metcalfe, December 2012 Rebecca Toone, December 2012 December 2014
Cycle Ergometry – Monark Ergometers Safety Information: Prior to performing exercise bouts with participants you must have read the following risk assessments: o 2013.0124RA_exercise_ergometry This standard operating procedure provides information on how to calculate a number of important variables when using Monark cycle ergometers. General Information about Monark Ergometers: The Monark Ergometer is a friction-based device meaning that the work-rate depends on the resistance applied to the flywheel basket and the pedal frequency. The flywheel basket weighs 1 Kg (Figure 1A) and resistance is increased by adding free weights to the basket (Figure 1B). The saddle height and position of the handle bars can be adjusted using the appropriate levers (Figure 2).
Figure 1 – Monark Flywheel Basket without (A) and with (B) weights.
Figure 2: Levers for adjusting handle bars (A) and Saddle Height (B) The Monark ergometer is portable but must be handled carefully. To move the ergometer, first ensure the flywheel basket is lowered and secure (otherwise the rope is prone to slip off the flywheel), then tilt the ergometer onto its wheels (from the front) using the handlebars. DO NOT LEAN ON THE PROTECTIVE PLASTIC COVERING OF THE ERGOMETER. 1. Calculating Work-Rate The Monark ergometer is a friction-braked device. Therefore, work-rate depends on both the resistance applied and the pedal frequency. Pedal frequency is maintained, while the amount of resistance applied is varied. It is important that subject’s cycle as close to 60rpm as possible for the duration of all exercise tests. Work = force x distance Force = mass (kg) x acceleration m.s-2 The force acting on a mass of 1kg at normal acceleration of gravity is 1 kilopond (kp), which equals 9.81 Newtons (N) The flywheel circumference is 1.622m. Therefore, the force is exerted over a distance of 1.622m during each flywheel revolution. As a result, when a mass of 1kg is applied to the ergometer, the work done per flywheel revolution is: (1 x 9.81 x 1.622) Nm = 15.9 Nm or 15.9 J Each time the pedal turns, the flywheel turns 3.7 times. Therefore, if a subject cycles at exactly 60 rpm, the flywheel turns 222 times (3.7 x 60). Subjects are
instructed to cycle at 60 revolutions per minute, and therefore work must be converted into a rate (J.s-1 or watts). (1 J.s-1 = 1 watts) 222 x 15.9 = 58.8 J.s-1 or watts 60 Using the flywheel counters fitted on the cycle ergometers it is possible to determine the exact number of times that the flywheel turns during a given amount of time. This figure should be entered into the above calculation in place of the number 222. 2. Calculating Mechanical Efficiency Metabolism during exercise is not 100% efficient at turning the energy derived from the catabolism of substrates into mechanical work. Indeed, it is relatively inefficient, and approximately 70-80% of available energy is released as heat, with only 20-30% being utilised for positive work. It is possible to calculate how efficient the body is at a particular activity: Mechanical Efficiency (%) = Work rate (kJ.min-1) Exercise-induced metabolic rate (kJ.min-1)
n.b. Exercise-induced metabolic rate is the product of exercising metabolic rate – resting metabolic rate. Also, note that workrate is expressed in kJ.min-1, which is converted from watts or J.s-1 to kJ.min-1 by multiplying by 60 and dividing by a 1000. 3. Calculating Relative Exercise Intensity The responses to exercise are largely governed by the relative intensity of a particular exercise, not the absolute intensity. Exercise at the same absolute work-rate (e.g. 100 W) will provoke very different responses in different subjects. Although the absolute level of work will be similar, and therefore the absolute oxygen cost also similar, the demands may be very different if expressed as a proportion of each individual’s maximum oxygen uptake. Relative exercise intensity may also be assessed in terms of heart rate at relative exercise intensity. 2 is known at a number of submaximal work-rates, then the linear Once VO relationship between oxygen uptake and work-rate can be determined. If this 2 max), is coupled to each individual’s personal maximum oxygen uptake ( VO 2012.1214SOP_cycle_ergometry_on_monarks
2 max may be derived. A similar relationship then a relative percentage of VO may be determined for heart rate (should be treated with more caution).
A worked example of how to calculate relative exercise intensity: Workrate (W): 2 (l.min-1) VO 2 max (l.min-1) VO
88 120 147 178 1.45 1.84 2.08 2.49 3.5
2 (put on the horizontal axis on this occasion), 1. Plot workrate against VO and derive a linear regression equation between these variables. This will enable the calculation of the workrate (y) required to elicit a certain percentage of maximum oxygen uptake. For the example above, the equation would be: y = -39.942 + 88.164 (x). 2 max that is required (e.g. 50%). In the 2. Calculate the percentage of VO example above, this would be 1.75 l.min-1.
3. Substitute this value (1.75) into the regression equation derived for your subject e.g. y = -39.942 + 88.164 (1.75). Therefore, the workrate required to elicit 2 max is 114 W. 50% of VO 4. Assuming that pedal revolutions will be 60 rpm (222 flywheel revolutions), calculate the actual mass that must be applied in order to elicit 114 W. Applied mass (kg) =
WR (W) x 60 9.81 x 1.622 x 222
Using the example given above, this would mean that 1.94 kg must be applied to the flywheel in order to produce a power output of 114 W, which in turn should elicit 50% of maximal oxygen uptake.
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