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Endurance Training – Lower Limb (intensity)

Mode | Intensity | Duration | Frequency | Type

 

Lower intensity continuous exercise training is as beneficial as high intensity continuous exercise training. Both high and low intensity interval training are also equally effective, however there may be a greater benefit from high intensity training performed in greater volumes (i.e. greater frequency, duration and length).4,5

Walking training intensity: It is recommended that for walking training a starting intensity should be 80% of the average six-minute walk test (6MWT) speed (see below how to calculate walking intensity from the results of a 6MWT) or 70% of the peak speed achieved on the incremental shuttle walk test (ISWT) (see below how to calculate walking intensity from the results of a ISWT).6,7

Cycle training intensity: It is recommended that a starting intensity for cycle training should be 60% of peak cycle work rate.  In many settings, the peak cycle work rate will not have been measured and exercise intensity may be titrated based on achieving a dyspnoea score or rate of perceived exertion score (RPE) of 3 to 4 on the modified BORG 0-10 scale.8

A. Prescribing intensity based on exercise test results

The results of a 6MWT or an ISWT can be used to prescribe training intensity for a walking program (over-ground walking or walking on a treadmill) and a stationary cycle program.  The calculations and examples for prescribing exercise intensity are provided below.

 

(i) Exercise intensity for walking laps – based on 6MWT

To calculate an appropriate intensity for walking laps: 80% x ([6MWD ÷ 6] x prescribed duration)


Six-minute walk distance (6MWD) ÷ 6 = Distance in one minute
For distance in 30 minutes = one minute distance x 30
For distance in 20 minutes = one minute distance x 20
For distance in 10 minutes = one minute distance x 10 etc…


The patient would not be expected to keep up the same walking pace throughout the walking training session that they achieved in the 6MWT. Therefore, prescribe 80% of the calculated distance by multiplying the prescribed duration distance by 0.8.

 

Example:

If the patient walked 220 m in six minutes:

  • One minute distance = 220 ÷ 6 = 36.7 m.
  • 30 minute distance = 36.7 x 30  = 1100 m.
  • 80% of 1100 = 880 m in 30 minutes.

 

If the distance of the over-ground walking track is known, this distance can be translated into a lap/track count.  Patients may find it easier to count the number of laps they need to walk, rather than the number of metres.

As an example for a walking training intensity of 880 m in 30 minutes, if the walking track is 32 m then the patient needs to walk 27.5 laps in 30 minutes (i.e. 880 ÷ 32 = 27.5 laps, prescribe 27 or 28 laps).

 


Tip: Translate the prescribed walking distance into a format the patient is familiar with.


 

At the beginning of a program, patients (particularly those who have been sedentary) may not be able to walk continuously for 30 minutes.  These patients should aim to start with 10 minutes of continuous walking, and build up to 30 minutes.

From the above example, if a 10-minute exercise session is deemed necessary at the start of the program, then this patient would need to walk 293 m (i.e. 880 m ÷ 3 = 293 m, rounded to 300 m).

 

(ii) Exercise intensity for walking on a treadmill – based on 6MWT

To calculate an appropriate intensity for walking on a treadmill: Treadmill speed = 80% x (6MWT average speed)


Treadmill speed = 80% x 6MWT average speed  


6MWT average speed = (6MWT distance x 10) ÷ 1000 km / hr


Note: On a treadmill the patient should be supervised and the speed adjusted by setting a slower speed initially until the patient has mastered the walking technique. Once the patient is confident and safe walking on the treadmill, increase the speed accordingly to the calculated walking speed.

 

Example:

If the patient walked 300 m in the 6MWT, then:

  • (300 x 10) ÷ 1000 = 3.0 km/hr.
  • 80% of 3.0 km/hr = 2.4 km/hr.

Therefore, the initial treadmill speed would be set at 2.4 km/hr. The treadmill may be started at approximately 1.5 – 2.0 km/hr to account for the patient being unfamiliar with treadmill walking.

 

(iii) Exercise intensity for walking laps – based on ISWT

The distance that the patient walked during the ISWT can be used to determine the walking speed for that patient’s walking program.

Use the table below to find the distance (m) that the patient walked and the corresponding walking speed (km/hr).

ISWT LevelSpeed DistancePredicted VO 2 peak Time / shuttle Number of shuttles
m/skm/hrmml/kg/min*secsleveltotal
10.51.80-304.4-4.92033
20.672.4140-705.2-5.91547
30.0843.0380-1206.2-7.212512
41.013.63130-1807.4-8.710618
51.184.25190-2508.9-10.48.57725
61.354.86260-33010.7-12.47.5833
71.525.47340-42012.7-14.76.67942
81.696.08430-52014.9-17.261052
91.866.69530-63017.4-19.95.461163
102.037.31640-75020.22-22.951275
112.27.92760-88023.2-26.24.621388
122.378.53890-102026.4-30.24.2914102

 

*VO2peak (ml/kg/min) = 4.19 + (0.025 x distance {m})

Patients would not be expected to walk at the speed shown on the table during their endurance exercise training session.  Therefore, only 75% of the peak speed should be prescribed as the walking speed (exercise intensity) for training.  At 75% of peak speed, the patient will be walking at approximately 60% of their predicted peak VO2.

At the beginning of a program, patients (particularly those who have been sedentary) may not be able to walk continuously for 30 minutes.  These patients should aim to start with 10 minutes of continuous walking, and build up to 30 minutes.

If the distance of the over-ground walking track is known, this distance can be translated into a lap/track count.  Patients may find it easier to count the number of laps they need to walk, rather than the number of metres.

 

Example:

If the patient walked 190 to 250 m during the ISWT, then:

  • The peak walking speed (as shown on the table) would be 4.25 km/hr (Level 5)
  • The training walking speed would be 75% of the peak speed 75% of 4.25 km/hr = 3.2 km/hr
  • Therefore, in one hour, the patient would be expected to walk 3.2 km
  • For a 30 minute training walk, the patient would walk 1.6 km
  • For a 20 minute training walk, the patient would walk approximately 1 km
  • For a 10 minute training walk, the patient would walk 0.5 km
  • The distance can be converted to a number of laps.  If the patient’s walking track was 32 m, then the patient would need to complete 31 laps within a 20-minute training walk session

1000 m ÷ 32 = 31 laps

 

B. Prescribing intensity based on dyspnoea assessments.

Research shows that levels of dyspnoea in patients with COPD can equate to levels of oxygen consumption6. Therefore, the patient’s level of dyspnoea may be used to monitor exercise intensity.

Most clinicians encourage their patients to exercise at a dyspnoea score of about 3-4  (“moderate” to “somewhat severe”) on the modified Borg 0-10 scale as this equates to exercising at a cycle training intensity of approximately 75% VO2 peak. Therefore, patients could be encouraged to exercise at this level of dyspnoea.

The use of the dyspnoea score can help patients equate the level of exercise that they perform during the supervised exercise program to the level of exercise that they have been asked to perform during their home exercise program. If they maintain a similar level of dyspnoea, they should be exercising at a similar intensity.

 

C. Prescribing exercise intensity for cycling based on 6MWT

The recommended intensity when prescribing cycle ergometry training is at least 60% of the peak work rate achieved on an incremental symptom-limited cycle ergometry test. However, clinically many patients do not undergo a cycle ergometry test.

Several published equations are available to estimate the initial work rate for prescribing cycle ergometry training based on the performance of a patient with COPD on the 6MWT. These equations have not been prospectively validated and their utility in the clinical setting has not yet been tested.9 An example is provided below to calculate cycle training intensity from the 6MWT.

Based on the 6MWT the following equation will give an estimate of the patient’s peak work rate (ref Hill).

Peak work rate (Watts)= (0.122 x 6MWD) +(72.683 x Ht [m]) – 117.109

Calculate 60% of this value as a starting intensity for cycle training. As this is only an estimated intensity, titrate the work rate so that the patient’s dyspnoea or rate of perceived exertion score is 3-4 on the Borg 0-10 scale. This should equate to exercising at about 78% of VO2 peak8