Non Exercise Estimations of O2max
Questionnaires can be used to predict a client’sO2max to gain insight into their physical activity levels and fitness. George et al (2007) used a method where an equation was used to predict O2max from the client’s BMI, gender, self rated functional ability (see appendix 3) and self rated physical fitness (See appendix 4) using the formula below:
O2max (mL ∙ kg-¹ ∙ min-¹) =
44.895+(7.042xGender)-(0.823xBMI)+(0.738xPFA)+(0.688xPAR)
Gender: Female = 0, Male =1
BMI=Weight (kg) /Height (m)²
PAR= Habitual Physical Activity (0-10)
PFA= Perceived Functional Ability (2-26)
Advantages of this method is that the unfit clients are not required to undergo and activity that may cause any discomfort. The procedure is fairly quick and can be fairly accurate. Despite the advantages of this method, limitations of this method could possibly outweigh the advantages in terms of error with interpretation and recall. Furthermore, deception may occur as the clients may not want to admit that they are sedentary.
BMI
In order to maintain a healthy weight it is important to measure ones weight regularly. This can be done via anthropometric measurements such as BMI. This method is a calculation that considers height in relation to body weight, Buchholz and Bugaresti, (2005) elaborate by explaining the calculation as: weight (kg) divided by height (m)². However, Heo, Faith and Pietrobelli, (2002) claim error occurs in this method as body composition is not accounted for. For example, a body builder and an obese individual may both have high BMI values above 30, yet the bodybuilder is not overweight and actually has a high fat free mass. Nevertheless, Tjepkema, (2006) and The World Health Report, (1998) would classify the body builder as obese.
Skin Folds
Alternatively, body fat can be measured using callipers on skin folds. This entails a pinch of skin to be taken from a particular location of the body (usually the right hand side of the middle of the back or the stomach area). This measures the subcutaneous fat in millimetres (Health Line, 2005). Limitations of this method occur when used on adolescents as they are growing at a quicker and more varied rate so that the measurements against age become unreliable. Other limitations include an uncomfortable situation for an overweight client and faults with the equipment.
Waist Circumference
Buchholz and Bugaresti, (2005) describe how waist circumference is measured, requiring the patient to stand with arms slightly away from the body and legs slightly parted. The tape measure is then placed around the abdomen in a parallel plane after normal expiration. Error occurs within this method as location of measurement is debated (Buchholz and Bugaresti, 2005), nevertheless, a recent study carried out by Wang et al, (2003) declares otherwise, finding that waist circumference measured in four various sites (immediately below the lowest rib, immediately above the iliac crest, at narrowest waist and midpoint between the lowest rib and the iliac crest) found little difference in total body fat in each sex.
Blood Pressure
Blood pressure is measured with a sphygmomanometer and is dependant on cardiac output and total peripheral resistance. High blood pressure (hypertension) is associated with obesity as larger volumes of oxygen and nutrients are required to greater amounts of fat tissue. According to Tuck et al, (1998) weight loss correlates with a reduction in blood pressure. A greater demand in oxygen and nutrients requires the heart to beat faster and work harder, pumping more oxygenated blood through additional blood vessels and therefore, the individual’s breathing increases, as well as heart rate (University of Virginia, 2007). This instigates more blood to circulate, increasing pressure of artery walls and therefore, blood pressure. The extra weight of overweight/obese individuals reduces the ability to transport blood through the vessels and can result in a heart attack. Blood pressure is measured when a client is sitting upright comfortably and has been relaxed for approximately five minutes with their back supported, feet touching the ground and their arm resting on a table at heart level. The appropriate size cuff is then selected and wrapped around the upper arm of the client inline with the brachial artery. The start button is pressed and the measurement is recorded. The procedure should be repeated 3 times and average is calculated. Limitations with this measurement is ‘white coat syndrome’ where the client feels intimidated or nervous in addition to any other exogenous factors which may affect blood pressure and therefore produce unreliable measurements.
Bioelectrical Impedance Analysis (BIA)
Bioelectrical impedance analysis measures body fat percentage and fat free body mass and has a similar accuracy rating as skin fold methods (Heyward, 1996), (Lockner et al, 1999) and (National Institutes of Health Technology Assessment Conference Statement,1996). The standard error estimate (SEE) for skin folds is 3.3% where as the SEE for single frequency bioelectrical impedance analysis (sfBIA) is 3.5% (Heyward, 2004). Despite the small error estimate associated with sfBIA, there is conflict within existing literature to the reliability of this method. While some studies report accuracy and reliability, (Jebb et al, 2007), (Andreoli et al, 2002) and (Utter et al, 1999) others conflict this thesis due to their findings and proving poor results (Frisard, Greenway and Delany, 2005) and (Deurenberg, 2006). Possible rationale for the errors found, may be due to inappropriate equations used or state of hydration within the individual as this has been shown to inflict error in terms of total body water, therefore overestimating fat-free mass and overall body composition (Hendel et al, 1996) and (Carella et al, 1997).
More recently, multi frequency bioelectrical impedance analysis was introduced and thought to be more accurate (Thompson et al, 2007) however, recent studies also show that this method also characterises flaws with respect to underestimating fat mass and percentage body fat (Pateyjohns et al, 2006), (Sun et al, 2005), (Neovius et al, 2006), and (Frisard, Greenway and Delany, 2005). Deurenberg, (2006) explains how BIA is based on the principle that an electrical current is sent around the body (Segal et al, 1985) and due to differing density of fat free mass and fat mass, the impedance can be measured from the resistance. Single frequency bioelectrical impedance uses a frequency of 50 kHz and therefore, due to the low frequency, only extracellular impedance is measured as the low current is unable to penetrate the cell membrane. The measured resistance is used to predict total body water (TBW) from the resistance index (RI=height2/measured resistance). The diffusion of water through the lean tissues is complex and many other factors previously mentioned could potentially alter the resistance of the tissue (). As fat is anhydrous, resistance index can then be used to estimate fat-free mass, using regression equations with more accurate techniques (). An estimate of fat mass can then be calculated by subtraction from the actual weight (Hannan et al, 1994). Fat free mass contains water where as fat mass is anhydrous, therefore fat free mass has a lower resistance and differing conductive and dielectric properties in comparison to fat mass. Due to fat free mass containing water, Minderico et al, (2008) express how error can occur during dehydrated and hyperhydrated states by skewing the results, either to under or over estimating body fat under false pretences. Wright et al, (2008) conveys that BIA can be measured by either using the body stat method (arm-leg) or via the Tanita method (leg-leg). However, both methods are found to be reliable and have gained recognition for use in hospitals and medical settings due to their non-invasive technique, practicality, efficiency and affordable qualities (National Institutes of Health Technology Assessment Conference Statement, 1996), (Powell et al, 2001) and (Wright et al, 2008). BIA is also preferred as it is portable and requires minimal training (Ritz et al, 2007), (Sun et al, 2005), (Neovius et al, 2006) and (Wattanapaiboon et al, 1998).
Dual Energy X-Ray Absorptiometry (DEXRA)
Dual energy x-ray absoptiometry is considered the ‘gold standard’ method of measuring body fat according to Mokdad et al, (2003). It is most commonly used to measure risk of osteoporosis but is also known to measure body fat. The process involves two x-ray beams with differing energy levels that scan the patient’s body to measure bone density by subtracting the amount of soft tissue (i.e. body fat). However, Deurenberg-Yap et al, (2000), Watts et al, (2006) and Van Der Ploeg, Withers and Laforgia, (2003) explain that this method is too costly and impractical to use in hospitals to measure body fat as there are alternative affordable whilst reliable methods of measure such as BMI, BIA and waist circumference. An additional criticism of this method originates from Gambacciani, (1999) who states that DEXRA is unable to distinguish between subcutaneous and intra abdominal fat.
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APPENDIX 1
TABLE 1- Predicted Maximal Oxygen Uptake
APPENDIX 2 - Åstrand-ryhming nomogram for the estimation of O2max from submaximal heart rate values on a step test.
APPENDIX 3- Physical Activity Rating (PAR) Questions
Select the number that best describes your overall level of fitness for the past 6 months.
0= Avoid walking or exertion, e.g. always use the elevator, drive instead of walking whenever possible.
1= Light activity: walk for pleasure, routinely use stairs, occasionally exercise sufficiently to cause heavy breathing or perspiration.
2= Moderate activity: 10-60 minutes per week of moderate activity such as golf, horseback riding, callisthenics, table tennis, bowling, weight lifting, yard work, cleaning house or walking for exercise.
3= Moderate activity for over 1 hour of activities decribed above
4= Vigorous activity; run less than a mile per week or spend less than 30 mins per week in comparable activity such as running/jogging, lap swimming, cycling, rowing, aerobics, skipping, running in place or engaging in vigorous aerobic activity such as soccer, basketball, tennis, racquetball, or handball
5= Vigorous activity: run 1 mile to less than 5 miles per week or spend 30 minutes to less than 60 mins per week in comparable activity as described above
6= Vigorous activity: run between 5 and 10 miles per week or spend between 1 and 3 hours per week in comparable activity described above
7= Vigorous activity: run between 10 and 15 miles per week or spend between 3 and 6 hours per week in comparable activity described above
8= Vigorous activity: run between 15 and 20 miles per week or spend between 6 and 7 hours per week in comparable activity described above
9= Vigorous activity: run between 20 and 25 miles per week or spend between 7 and 8 hours per week in comparable activity described above
10= Vigorous activity: run over 25 miles per week or spend over 8 hours per week in comparable activity described above
APPENDIX 4- Perceived Functional Ability (PFA) Questions
Suppose you were going to exercise continuously for 1 mile. Which exercise pace is most applicable to you i.e. not too easy, not too hard. Circle the appropriate number (1-13)
1 Walking at a slow pace (18 mins per mile or more)
2
3 Walking at a medium pace (16 mins per mile or more)
4
5 Walking at a fast pace (14 mins per mile or more)
6
7 Jogging at a slow pace (12 mins per mile or more)
8
9 Jogging at a medium pace (10 mins per mile or more)
10
11 Jogging at a fast pace (8 mins per mile or more)
12
13 Walking at a fast pace (7 mins per mile or more)
How fast could you cover a distance of 3 miles and not become breathless or overly fatigued. Be realistic. Circle the appropriate number (1-13)
1 I could walk the entire distance at a slow pace (18 mins per mile or more)
2
3 I could walk the entire distance at a medium pace (16 mins per mile or more)
4
5 I could walk the entire distance at a fast pace (14 mins per mile or more)
6
7 I could jog the entire distance at a slow pace (12 mins per mile or more)
8
9 I could jog the entire distance at a medium pace (10 mins per mile or more)
10
11 I could jog the entire distance at a fast pace (8 mins per mile or more)
12
13 I could run the entire distance at a fast pace (7 mins per mile or more)
