Target RPE at the Ventilatory Threshold

, Michael GallagherJr.2 and Robert J. Robertson3



(1)
Lock Haven University of Pennsylvania, Lock Haven, PA, USA

(2)
University of Central Arkansas, Conway, AR, USA

(3)
University of Pittsburgh, Pittsburgh, PA, USA

 



Keywords
Ventilatory threshold (VT)Heart rate (HR) rangeHR at the VT (HR-VT)RPE at the VT (RPE-VT)Group-normalized perceptual response


The ventilatory threshold (VT) is an important physiological marker of the exercise intensity at which an individual can sustain performance for a prolonged period, and therefore is an important determinant of aerobic exercise performance capacity. Determination of the exercise training intensity equivalent to the VT is an important measure for both elite athletes and sedentary individuals. Training at the intensity equivalent to the individual’s VT provides an optimal overload stimulus to achieve both performance and health-fitness benefits. Identification of the VT in the laboratory setting requires experienced personnel and expensive laboratory equipment. Therefore, a surrogate measure of the VT is needed to guide exercise training intensity. This can be achieved by identifying a target HR associated with the VT (HR-VT). However, exercise HR can be affected by both environmental and clinical conditions and requires skill for accurate palpation when a HR monitoring device is unavailable. RPE has been validated for the prescription and regulation of exercise in a variety of settings and subject populations. Owing to its ease of use and cost-efficiency, a target RPE associated with the VT (RPE-VT) presents a practical method for prescribing exercise at VT intensity. The primary purpose of this laboratory experiment is to determine RPE-VT, using both the Borg and OMNI Scales, and HR-VT during load-incremented aerobic exercise.


7.1 Background



7.1.1 Ventilatory Threshold


The VT (also known as the ventilatory breakpoint) can be defined as the point during dynamic exercise of increasing intensity when V E begins to increase at a rate disproportionately faster than that of VO2. Some investigations refer to this as the 1stVT inflection point because a further increase in V E resulting in a 2ndVT inflection point (i.e., 2ndVT) often follows the 1stVT during load-incremented exercise tests (Alberton et al. 2013). The experiment described later in this chapter employs the 1stVT. This increase in V E occurs as the body attempts to expel excess carbon dioxide produced as a result of an increased reliance on anaerobic metabolism to meet the energy requirements of higher intensity exercise. The VT occurs at approximately the same exercise intensity or VO2 as the lactate threshold (LT). The LT can be defined as the point during exercise of increasing intensity when the clearance of lactate from the blood can no longer keep up with the increased rate of lactate production by muscle. During exercise of progressively increasing intensity, blood lactate begins to accumulate above resting values owing to an increased reliance on anaerobic metabolism. In the typical adult, the VT and LT occur between 55 and 70 % of VO2max (Kenney et al. 2012).

Identifying the VT is very important when developing training programs for elite endurance athletes because it marks the highest exercise intensity that an individual can sustain for a prolonged period. The VT is a better indicator of performance in endurance athletes than VO2max because one cannot sustain the intensity at which VO2max occurs for extended periods. In addition, an athlete’s VO2max and ability to increase VO2max with training have a significant hereditary determinant. Twenty-five to 50 % of the variance in VO2max can be explained by genetic factors (Kenney et al. 2012). However, once an elite athlete achieves genetically determined VO2max through aerobic training, the athlete can continue to increase endurance performance through further increases in VT. Elite endurance athletes have been known to increase their VT to 80–90 % of VO2max.

The VT can also be used for exercise prescription and programming for non-athletes. The exercise training intensity equivalent to the VT provides an optimal overload stimulus to achieve health-fitness benefits, including weight loss and the improvement of cardiorespiratory fitness. When individuals are allowed to self-select aerobic exercise intensity, many choose intensities similar to the VT (Dishman et al. 1994; Ekkekakis and Lind 2006; Lind et al. 2005). However, at exercise intensities above the VT, marked decreases in self-reported pleasure begin to occur that may lead to cessation of exercise and subsequent dropping out from an exercise program (Acevedo et al. 2003; Bixby et al. 2001; Ekkekakis et al. 2004; Hall et al. 2002).

Direct assessment of the VT or LT is often impractical because it requires expert personnel and expensive laboratory equipment. Generally, an individual must undergo a load-incremented exercise test terminating at maximal intensity in order to adequately measure all of the physiological variables necessary to determine the VT or LT. For many with cardiovascular risk factors, such a maximal GXT may require continuous heart monitoring using an electrocardiograph (ECG) and direct physician supervision. To measure the VT, a respiratory-metabolic measurement system is required. This automated system determines the individual’s volume of expired air, VO2, and the volume of CO2 production (VCO2). This system requires the individual to wear a respiratory apparatus including a head support, mouthpiece and nose clip. These can be uncomfortable and would not be worn during a normal exercise session. To measure the LT, venous or capillary blood samples are taken at regular intervals throughout the exercise test. These invasive measurement procedures can be painful and psychologically stressful.


7.1.2 Target HR at the VT for Exercise Prescription


The calculation of a target HR associated with the VT (HR-VT) has been proposed as an inexpensive method to estimate this important marker of anaerobic metabolism. It is recognized that the target HR method may be more practical and much less expensive than respiratory-metabolic methodology to identify the VT. However, the HR response to exercise can be affected by psychological stress and the body’s need for thermoregulation, especially during exercise in high ambient heat and humidity. When measurements are performed outside of a controlled laboratory environment, there may be considerable variability in HR-VT. In addition, when an exercise prescription is based on a target HR, the individual must be able to measure HR during exercise. This requires skill if measuring HR by palpation, additional cost if using a HR monitoring system, or restriction to a fitness facility where HR can be measured using monitors attached to available ergometers.


7.1.3 Target RPE at the VT for Exercise Prescription


RPE can be used to prescribe and regulate exercise in a variety of athletic, clinical and pedagogical settings (Goss et al. 2003) and can be used in place of or in addition to traditional exercise prescriptions based on HR. Rather than prescribe exercise based on a target HR range, one can prescribe exercise using a target RPE. This application is justified because for most exercise modalities RPE is more closely linked to prescribed levels of VO2 than HR (Goss et al. 2011; Noble and Robertson 1996).

The RPE used in an exercise prescription is selected based on its correspondence to a specific physiological intensity, such as the VT, a %VT or a %VO2max. A target RPE at the VT (RPE-VT) can be identified using responses to a perceptual estimation test protocol including measures of VO2. Once the RPE-VT is calculated, the individual is taught to self-regulate exercise intensity to produce the specified target RPE. It should be noted that when an exercise prescription is based on a target RPE, the client should have a firm knowledge of the RPE scale and its use during exercise. Such familiarization with the RPE scale can be established when the instructional set and anchoring procedures are administered as part of the test orientation.

Goss and colleagues (2003) defined the group-normalized perceptual response as a range of RPE’s that corresponds to a target physiological outcome during exercise and that is common to a specified group of individuals. The use of group-normalized RPE to prescribe and monitor exercise intensity has application to a variety of activities for a wide range of individuals as it is comparatively easy to determine and is readily understood by the participant (Goss et al. 2003). The group-normalized RPE-VT may be a more practical method to establish an optimal training intensity (i.e., zone) to improve cardiorespiratory fitness than the VT or LT which must be determined by laboratory-based exercise testing (Goss et al. 2011). The measurement of RPE does not require expensive equipment or extensive technical skill as do determination of the VT or LT.

Many individuals choose to exercise at intensities near to or just below their VT. However, studies have shown that a substantial number of individuals would not prefer to exercise at intensities above the VT because these levels induce unpleasant feelings and psychological distress (Lind et al. 2005). As such, prescription of exercise intensities above the VT may lead to a decrease in exercise adherence. Therefore, it is important in the health-fitness setting to have a simple, inexpensive method to identify a physiologically optimal training intensity that is subjectively acceptable to the participant. In this context, the RPE-VT may be useful to identify the upper-limit of a prescribed exercise intensity range, especially for beginning exercisers who are psychologically intolerant of high-intensity aerobic exercise. In addition, the RPE-VT is a perceptual marker that can be used to identify the optimal training intensity for elite endurance performers. Competitive cyclists and runners can use the RPE-VT during training and races alike to produce their optimal performance pace, especially when HR and VO2 monitoring are not practical or not allowed (Monnier-Benoit et al. 2009).


7.1.4 Evidence for the RPE-VT: Borg and OMNI Scales


Studies have found RPE-VT to range from 11 to 14 using the Borg (6 to 20) Scale in a wide variety of subjects (Alberton et al. 2013; Ekkekakis et al. 2004; Feriche et al. 1998; Hill et al. 1987; Mahon et al. 1998; Purvis and Cureton 1981; Swaine et al. 1995). A recent study by Elsangedy and colleagues (2013) compared RPE-VT between sedentary women who were normal weight, overweight, and obese as classified by body mass index (BMI). RPE-VT was a mean of ~12 on the Borg Scale regardless of BMI classification (Elsangedy et al. 2013). A recent study by Alberton and colleagues (2013) determined Borg Scale RPE at the 1stVT and 2ndVT inflection points during treadmill exercise and three different water aerobic exercises: stationary running, jumping jacks, and forward kicks. Mean RPE-VT for the 1stVT ranged from 12 to 13, while mean RPE-VT for the 2ndVT ranged from 15 to 16 (Alberton et al. 2013).

Studies investigating the RPE-VT using the OMNI Scale have observed values ranging from 5 to 7 (Fig. 7.1). Goss and colleagues (2011) identified a mean RPE-VT of 5.1 in Division I football players performing treadmill exercise. RPE was assessed by the Adult OMNI Walk/Run RPE Scale. Robertson et al. (2001) identified a mean OMNI RPE-VT of 6.1 in children of average and above average fitness levels performing cycle ergometer exercise. In addition, Robertson et al. (2007) identified the RPE-VT in children using direct observation, rather than subject estimation, with OMNI RPE values ranging from 6 to 6.5. These results derived from the OMNI Scale seem to be in agreement with previous research using the Borg Scale. This comparison can be done using Robertson’s (2004) table to convert RPE between the Borg and OMNI Scales (Fig. 7.2). Using this table, OMNI RPE values ranging from 5 to 7 correspond to Borg Scale RPE values of 12 to 16.

A310442_1_En_7_Fig1_HTML.gif


Fig. 7.1
OMNI Scale RPE-VT Zone (Robertson 2004)


A310442_1_En_7_Fig2_HTML.gif


Fig. 7.2
RPE conversions between the OMNI Scale and Borg (6–20) Scale (Robertson 2004)


7.1.5 Case Study



7.1.5.1 Client Information


A 21-year-old male college student comes to your fitness facility. During a pre-participation interview prior to exercise testing, he tells you that he plays recreational basketball once or twice per week. He describes that he gets “winded” easily when playing a full court game. He also tells you that he exercises on a stationary bike at his school’s student fitness center once or twice per week for 10–20 min per session. He is moderately overweight and he describes his fitness level as average. His goals are to lose weight and increase his aerobic fitness. He enjoys going to the fitness center because he can go with a friend or watch television while exercising and he prefers the bike over the treadmill. He knows he should go to the fitness center more often. He wants to learn the proper exercise intensity to perform on the bike so he can meet his goals and perform better on the basketball court. Due to the client’s age, health status, and current level of PA, a pre-participation GXT is likely not required. Therefore, his exercise prescription could be developed using a group-normalized RPE-VT.


7.1.5.2 Assessments


Perform a graded exercise test on a cycle ergometer or treadmill terminating at maximal exertion to determine CRF (VO2peak/max), the VT, and RPE-VT. These test responses, when incorporated into an exercise prescription, will identify an effective exercise intensity to achieve his weight loss and aerobic fitness goals.


7.1.5.3 Results and Analysis






  • Identify HRmax/peak (b · min−1):


  • Identify VO2max/peak (ml · kg−1 · min−1 or l · min−1):


  • Identify the VT (ml · kg−1 · min−1 or l · min−1, %VO2max/peak, PO):


  • Identify OMNI RPE-VT:


  • Identify HR-VT (b · min−1):

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May 22, 2017 | Posted by in SPORT MEDICINE | Comments Off on Target RPE at the Ventilatory Threshold

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