Aerobic capacity of young Mexican American adults

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International Journal of Industrial Ergonomics 35 (2005) 91–103 www.elsevier.com/locate/ergon

Aerobic capacity of young Mexican American adults Arunkumar Pennathur, Amit Lopes, Luis Rene Contreras Mechanical and Industrial Engineering Department, University of Texas at El Paso, El Paso, TX 79968-0521, USA Received 29 January 2004; accepted 16 August 2004 Available online 8 October 2004

Abstract This research’s main objective was to determine aerobic capacity in Mexican American young adults. Aerobic capacity was measured using a submaximal treadmill exercise using the Bruce protocol. Sixteen male and five female healthy student volunteers aged 22–30 participated in the experiment. Volumetric oxygen consumption was measured using the breath-by-breath VMaxST oxygen consumption monitor. Results indicate that Mexican American men had a VO2max of 4.8 l/min (SD=1.75) and a weight adjusted VO2max of 56.32 ml/kg/min (SD=12.2), while Mexican American women had a VO2max of 2.8 l/min (SD=0.73), and a weight-adjusted VO2max of 44.69 ml/kg/min (SD=6.72). Results also indicated that the heart rate was nearly 10 times the rating of perceived exertion at each workload. Relevance to industry Given the changing demographics of the US population, and the work force becoming predominantly Hispanic, it is important to quantify the aerobic capacity of Mexican American young adults for work design. r 2004 Elsevier B.V. All rights reserved. Keywords: Mexican American young adults; Aerobic capacity; Physical work capacity

1. Introduction Recent statistics from the Bureau of Labor Statistics (BLS) show that nearly 8% of the US workforce consists of workers of Mexican origin. Furthermore, 64% of Hispanic workers in the US are of Mexican origin. Statistics from BLS also indicate that nearly 13% of Mexican American Corresponding author. Fax: +1 915 747 5019.

E-mail address: [email protected] (A. Pennathur).

workers are engaged in tasks requiring heavy manual work. Several recent studies show that Hispanic Americans, particularly, Mexican Americans, have greater incidences of cardiovascular diseases in the US than other ethnic groups (Goff et al., 1993a, b, 1997). Based on the Corpus Christi Heart Project, and on an analysis of surveillance data for hospitalized coronary heart disease events Mexican Americans experienced greater incident events than non-Hispanic whites (Goff et al., 1997). Recently compiled data from the American

0169-8141/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ergon.2004.08.008

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Heart Association (2002), show that Hispanic men and women have higher risk of developing cardiovascular diseases than other groups. The National Health and Nutrition Examination Survey found that 53% of Mexican American men (ages 20–74) and 48% of Mexican American women (ages 20–74) had total blood cholesterol levels over 200 mg/DL. This is in comparison of 52% and 49% for non-Hispanic whites of the same age, and 45% and 46% for non-Hispanic blacks of the same age. The estimated age-adjusted prevalence among Americans aged 20 and above with LDL cholesterol levels of 130 mg/DL or higher was 46.3% for Mexican American men and 41.6% for women. Studies on dietary trends among different ethnic groups (Siega-Riz and Popkin, 2001; Tortolero et al., 1997; D’Agostino et al., 1996) tend to largely confirm these findings. Physical inactivity, another important factor that can result in a reduction in maximal aerobic power, was more prevalent among Hispanic Americans than other groups (Pescatello et al., 2000).The National Health Interview Survey conducted by the National Center for Health Statistics shows that among adults aged 18 and older, nearly 50% of Hispanic men and 57% of Hispanic women have no leisure time physical activity. Among adults aged 20–74 (with a body mass index (BMI) of 25 and higher to indicate an overweight condition, and a BMI of 30 or higher to indicate obesity), nearly 69% of both Mexican American men and women were found to be overweight; nearly 25% of Mexican American men, and 36% of Mexican American women were found to be obese (Steffen-Batey et al., 2000). Given the increasing numbers of Mexican American workers in the industrial workforce in the US, and given the higher prevalence of risk factors for cardiovascular problems in this group, it is important to determine if the physical working capacity of Mexican American workers are any different from other industrial working groups. If the physical working capacity of Mexican American workers is found to be different from other industrial working groups, it will impact work design limits for manually demanding tasks. Before such comparisons can be made, however, it is critical to obtain estimates of aerobic capacity

of Mexican American adults in the working age group. The objective of this study was to quantify the maximal aerobic capacity of young Mexican American adults.

2. Materials and methods 2.1. Study participants Participants in this study were five young females and sixteen young males (ages 22–30) recruited from the industrial and manufacturing engineering student body at the University of Texas at El Paso. All male participants in this study reported one or more years of experience working in the manufacturing/warehousing industry in the twin-plant industry in El Paso. Female participants in the study, however, had no experience working in the local industry. A health status questionnaire recommended by the American College of Sports Medicine (2000) indicated that of the five female participants, only one smoked a cigarette. Among males 18% smoked cigarettes. Two out of the five females exercised regularly and 44% of the males exercised regularly with an average of 4 days/week. Based on the classification of overweight and obesity by the National Heart, Lung, and Blood Institute (1998) expert panel on the identification, evaluation and treatment of obesity in adults, one of 16 males was extremely obese (BMIX40 kg/m2), 2 were obese (BMIX30 kg/m2), 9 were overweight (BMI between 25 and 29.9 kg/m2) and 4 were normal (BMI between 18.5 and 24.9 kg/m2). One female out of the 5 was overweight, and the rest had normal body mass indices. Studies have shown that first generation Mexican–American Males who were younger acculturated more rapidly than females or older people (Vega et al., 1987; Burnam et al., 1987). Since this study’s participants were University students of Mexican origin residing here in the US, the degree of acculturation was not measured and participants were expected to have acculturated to the American culture. Other participant characteristics are presented in Table 1.

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Table 1 Participant characteristics Participant characteristic

Age (years) Height (cm) Weight (kg) BMI (kg/m2)

Males

Females

Mean

SD

(Min, Max)

Mean

SD

(Min, Max)

23.94 175.88 86.45 28.13

2.38 7.24 11.91 5.22

(20, 28) (160, 186) (63.5, 112) (23.32, 43.75)

22.6 161.8 62 23.68

0.89 12.7 8.49 2.12

(22, 24) (150, 179) (50, 68) (21.22, 26.56)

Fig. 1. The VmaxST portable metabolic monitor.

2.2. Experimental methods 2.2.1. Equipment used A GE Marquette Series 2000 treadmill, with an automatic treadmill controller was used in this experiment. Oxygen uptake was measured using the VMaxST portable breath-by-breath metabolic measurement system (Fig. 1). Heart rate was quantified using a Polar Heart Rate transmitter—the VMaxST metabolic measurement system also recorded the heart rate. The Rating of Perceived Exertion was measured using the Borg’s Rating of Perceived Exertion scale. 2.2.2. Protocol for measurements The first session included a screening test using the ACSM health questionnaire and the measurement of height and weight. Participants then completed the informed consent form approved by the Institutional Review Board for Human

Subjects. Participants were then scheduled for the actual test. The second session consisted of the actual experiment. Before testing, the VMaxST unit was calibrated for volume, gas (O2/CO2) and pressure. After calibration, participants were asked to perform treadmill exercise at three submaximal work rates. The Bruce Treadmill Exercise submaximal testing protocol, which has been recommended by the American College of Sports Medicine (ACSM, 2000) for use with younger individuals who are expected to be more physically active, was used in the experiment. Each workload was 3 min long with the lowest workload for the first stage set at 1.7 mph speed and 10% gradient. At each workload setting, participants’ oxygen uptake was continuously measured using the VMaxST. Heart rate was also monitored at each load. Measurements of heart rate and oxygen consumption were taken once they stabilized and reached steady state values. The steady state values of oxygen consumption and heart rates were then used to generate a x–y graph, with heart rate on the xaxis and the oxygen consumption on the y-axis. A straight line was drawn between the plotted submaximal points on the x–y graph. Maximal heart rate for each participant was estimated from the age-adjusted formula (Cooper et al., 1975), Maximal heart rate=(214 0.71Age) (in years), and plotted on the x-axis. Using this estimated value of maximum heart rate, and a plot of the submaximal oxygen consumption and corresponding submaximal heart rates generated from the experimental protocol at each submaximal workload, a vertical line was projected from the maximum heart rate point to intersect with the

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plotted line on the x–y graph. The maximal oxygen consumption was then estimated by projecting the intersection point along the line into the corresponding y-axis coordinate. Participants also rated their perceived exertion at all workloads using the category RPE scale.

and females, respectively, at various workloads. Results indicate that, for both males and females, VO2, heart rate and RPE progressively increase with increasing workload. Furthermore, heart rate was found to be approximately 10 times that of the RPE at each workload for both men and women. For males, the mean VO2 was 39.1% of the VO2max at the end of workload 1, 50.3% at the end of workload 2 and 65.6% at the end of workload 3. For females, the mean VO2 was 46.2% of the VO2max at the end of workload 1 and 59.4% at the end of workload 2. Heart rate and oxygen consumption at the end of each workload for

3. Results Table 2 presents maximum heart rates and maximal oxygen consumption values for males and females in the experiment. The average maximal oxygen consumption was found to be 4.8 l/min (SD=1.75 l/min) for males and 2.8 l/min (SD=0.73 l/min) for females. Male–female differences in magnitude of oxygen consumption, heart rate and RPE at different workloads, were calculated based on maximum values of corresponding variables for males, and are shown in Figs. 2–4 respectively. Overall, maximum oxygen consumption (l/min) for females was 58.33% that of the males. The weight-adjusted maximum oxygen consumption (ml/kg/min) for females was 79.4% that of the males. Oxygen consumption in females was 40.4% after workload 1 and 52% after workload 2 of the maximum male oxygen consumption. Heart rates for females at workload 1 and 2 were 83.3% and 96%, respectively, of the maximum heart rate for males. The RPE was 76.4% and 101% of the maximum RPE for males. Tables 3 and 4 present VO2 data for males and females, respectively, at various workloads. Tables 5 and 6 present heart rate and RPE data for males

%VO2 males %VO2 females 80 Percentage VO2

70 60 50 40 30 20 10 0 Workload 1 Workload 2 Workload Intensity Fig. 2. Female and male VO2 (%) with increasing workload intensity (Percentage VO2 represents workload VO2 normalized with respect to male VO2 at workload 3; females were not subjected to workload 3).

Table 2 HRmax and VO2max Variable

Maximal heart rate (Beats/Min)

VO2max (l/min)

VO2max (ml/kg/min)

Mean

SD

(Min, Max)

Mean

SD

(Min, Max)

Mean

SD

(Min, Max)

Males (n=16)

197.1

1.75

(194, 200)

4.8

1.0

(3.05, 6.3)

56.32

12.2

(27.2, 75.9)

Females (n=5)

197.8

0.45

(197, 198)

2.8

0.73

(1.9, 3.5)

44.69

6.72

(35, 52.1)

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%HR males

95

in accordance with the proven linear relationship between heart rate and oxygen consumption.

%HR females 120

4. Discussion Percentage HR

100 80 60 40 20 0 Workload 1 Workload 2 Workload Intensity Fig. 3. Female and male HR (%) with increasing workload intensity (Percentage HR represents workload HR normalized with respect to male HR at workload 3; females were not subjected to workload 3).

%RPE males %RPE females

Percentage RPE

120 100 80 60 40 20 0 Workload 1 Workload 2 Workload Intensity Fig. 4. Female and male RPE (%) with increasing workload intensity (Percentage RPE represents workload RPE normalized with respect to male RPE at workload 3; females were not subjected to workload 3).

males were linearly related (po0.05). Heart rate and weight-adjusted oxygen consumption (ml/kg/ min) at the end of each workload for males was also significantly linearly related (po0.05). This is

Aerobic capacity, as measured by VO2max for Mexican American young male adults in this study was found to be 4.8 l/min (SD=1.75). Body weight adjusted maximum volumetric oxygen consumption was 56.32 ml/kg/min (SD=12.16). Although a statistical comparison of results from this study was not performed with results from other studies that report aerobic capacities of other young male adults measured using treadmill running, results this study indicate that overall magnitudes of aerobic capacity measures are comparable. Astrand et al., (1973), with 31 male (average age 26.9) physical education college students from Sweden reported a VO2max of 4.08 l/min (SD=0.07), and a body weight adjusted VO2max of 58.7 ml/kg/min (SD=0.7). MacNab et al. (1969) reported a mean VO2max of 3.92 l/min (SD=0.58), and a body weight adjusted mean VO2max of 51.7 ml/kg/min (SD=5.1) for 24 male college students from Canada. In a study of 23 American men who were college students, McArdle and Magel (1970) reported that mean VO2max and body weight adjusted VO2max values of 3.27 l/min (SD=0.51) and 42.7 ml/kg/min (SD=4.9), respectively. In a study of laborers from Colombia, Maksud et al. (1976) reported a mean VO2max of 2.7 l/min (SD=0.48), and a mean body weight adjusted VO2max of 44.1 ml/kg/min (SD=3.9). Vogel et al. (1986), in a study of new army recruits (without any formal physical training and considered equivalent to a typical US civilian young adult population), reported that the mean VO2max was 3.6 l/min (SD=0.5). The mean body weight adjusted VO2max in their study for the 210 males was 51.1 ml/kg/min (SD=5.1). More recently, Founooni-Fard and Mital (1993), have reported that the treadmill aerobic capacity for 10 adult male students (age range 19–35 years) was 3.5 l/min (SD=0.77). Vitalis et al. (1994), in a study of 14 Greek steelworkers (average age 43, SD=11.2), reported a mean VO2max of 2.44 l/min (SD=0.55), and a weight

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Table 3 VO2 at various workloads for males (n=16) VO2 (l/min)

W1 W2 W3

VO2 (% of VO2max)

Mean

SD

(Min, Max)

Mean

(Min, Max)

1.84 2.37 3.12

0.30 0.38 0.58

(1.38, 2.40) (1.62, 3.26) (2.04, 4.06)

39.1 50.3 65.6

(27.9, 53.4) (38.5, 63.6) (54.2, 78.8)

W1, W2 and W3 refer to workload stages 1, 2, and 3, respectively.

Table 4 VO2 at various workloads for females (n=5) VO2 (l/min)

W1 W2

VO2 (% of VO2max)

Mean

SD

(Min, Max)

Mean

(Min, Max)

1.26 1.63

0.19 0.31

(1.03, 1.49) (1.26, 1.94)

46.2 59.4

(37.8, 52.6) (51.8, 64.8)

Table 5 Heart rate and RPE at various workloads for males (n=16) Workload

W1 W2 W3

Heart rate (beats/min)

RPE

Mean

SD

(Min, Max)

Mean

SD

(Min, Max)

108.19 122.44 146.69

11.01 10.28 10.26

(86, 125) (104, 141) (130, 166)

9.63 12.25 15.19

2.0 1.65 1.47

(7, 13) (9, 15) (13, 17)

Table 6 Heart rate and RPE at various workloads for females (n=5) Workload

W1 W2

Heart rate (beats/min)

RPE

Mean

SD

(Min, Max)

Mean

SD

(Min, Max)

122.2 140.8

6.05 5.89

(116, 132) (134, 149)

11.6 15.4

1.67 1.67

(9, 13) (13, 17)

adjusted VO2max of 33.9 ml/kg/min (SD=8.9). Jackson et al. (1995) studied 145 college educated, white collar male employees at NASA/Johnson Space Center. These men were from 25 to 34 years of age. Maximal volumetric oxygen consumption

after adjusted for body weight was estimated at 45.8 ml/kg/min (SD=7.7). VO2max was estimated at 3.573 l/min (SD=0.675). Lee et al. (1995) reported that the VO2max of 12 Chinese male college students (mean age=21.2, SD=1.88) was

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3.107 l/min (SD=0.41), with a weight adjusted VO2max of 47.20 ml/kg/min (SD=3.67). Mamansari and Salokhe (1996) studied the physical working capacity of agricultural laborers in Thailand. Ten men aged 20–52, participated in a submaximal bicycle ergometer test to determine aerobic capacity. Their results indicate that the mean VO2max is 2.072 l/min (SD=0.57), and the mean weight adjusted VO2max is 36.84 ml/kg/min (SD=9.09). Bhambani and Maikala (2000), in a study of 11 healthy college males (average age 25.1; SD=3) from Canada, found that the maximal oxygen uptake was 4.46 l/min (SD=0.69), and the body weight adjusted maximal oxygen uptake was 56.9 ml/kg/min (SD=7.1). Lloyd and Cooke (2000), in their study with 4 young male participants from the United Kingdom (average age 26.5 years, SD=4.5), report a weight adjusted VO2max of 53.7 ml/kg/ min (SD=10). Kirk and Sullman (2001) in their study on four male cable hauler choker setters in the logging industry in New Zealand, using a cycle ergometer and a submaximal method, estimated a VO2max of 4.2 l/min (SD=0.82) and a weight adjusted VO2max of 56.5 ml/kg/min (SD=11.82). Woo et al. (2001), in their study of 11 male Korean university students (mean age 25, SD=1.21), found that the VO2max using a treadmill was 2.87 l/min (SD=0.33), and that the weight adjusted VO2max was 42.31 ml/kg/min (SD=4.04). Woo et al. (2001) also found that the corresponding estimates of aerobic capacity for males using a cycle ergometer were 2.61 l/min (SD=0.29), and 38.48 ml/kg/min (SD=4.55), respectively. The number of female participants in this study was small (n=5). Aerobic capacity, as measured by the VO2max for Mexican American young female adults in this study was found to be 2.8 l/ min (SD=0.73). Body weight adjusted mean maximum volumetric oxygen consumption was 44.69 ml/kg/min (SD=6.72). Astrand et al. (1973), with 35 female (average age 21.9) physical education college students from Sweden reported a VO2max of 2.83 l/min (SD=0.05), and a body weight adjusted VO2max of 47.6 ml/kg/min (SD=0.7). MacNab et al. (1969) reported a mean VO2max of 2.32 l/min (SD=0.41), and a body weight adjusted mean VO2max of 39.1 ml/kg/min

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(SD=5.1) for 24 female college students from Canada. In a study of 20 American women physical education students, Higgs (1973) reported mean body weight adjusted VO2max value of 41.3 ml/kg/min (SD not reported), respectively. Vogel et al. (1986), in a large study of 212 new army recruits (without any formal physical training and considered equivalent to a typical US civilian young adult population), reported that the mean VO2max was 2.18 l/min (SD=0.32). The mean body weight adjusted VO2max in their study for the 212 females was 37.4 ml/kg/min (SD=3.7). Mamansari and Salokhe (1996) studied the physical working capacity of agricultural laborers in Thailand. Ten women aged 25–55, participated in a submaximal bicycle ergometer test to determine aerobic capacity. Their results indicate that the mean VO2max is 1.38 l/min (SD=0.23), and the mean weight adjusted VO2max is 25.52 ml/kg/min (SD=4.19). Bhambani and Maikala (2000), in a study of 11 healthy college females (average age 23.7; SD=2.8) from Canada, found that the maximal oxygen uptake was 2.86 l/min (SD=0.33), and the body weight adjusted maximal oxygen uptake was 44.6 ml/kg/min (SD=7.6). Lloyd and Cooke (2000), in their study with 5 young female participants from the United Kingdom (average age 23.3 years, SD=4), report a weight adjusted VO2max of 45.5 ml/kg/min (SD=4.5). Woo et al. (2001), in their study of 13 female Korean university students (mean age 20, SD=0.96), found that the VO2max using a treadmill was 2.057 l/min (SD=0.314), and that the weight adjusted VO2max was 37.01 ml/kg/min (SD=6.64). Woo et al. (2001) also found that the corresponding estimates of aerobic capacity for females using a cycle ergometer were 1.853 l/ min (SD=0.227), and 33.54 ml/kg/min (SD=4.37), respectively. A comparison of the overall magnitudes of VO2max and weight adjusted VO2max from this study for Mexican American young university women and results from other similar female university students, again, shows that there may not be significant differences in aerobic capacities of young women of Mexican origin and young women from other countries. Based on the VO2max data from this study, it is also apparent that at workload 1, male

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participants in this study used on the average 39.1% of their VO2max. This number increased to 50.3% for the second workload level. At maximum workload, male participants used 65.6% of their age-predicted VO2max. Comparatively, females in this study used more of their VO2max at workload 1 (about 7% more than males at workload 1). This number for females increased to about 9% more than males at workload 2. Female participants in the study were unable to continue the exercise beyond the 2nd workload stage of the protocol. When compared with males (average of male VO2max taken as 100%), female participants in this study had 58.33% of male aerobic capacity. The equivalent weight adjusted female capacity was 79.4% compared to average of male VO2max. Several other studies have reported similar results when comparing the aerobic capacity of young men and women. Vogel et al. (1986), for instance, reported a 39% difference between VO2max of men and women in their study. Furthermore, Vogel et al. observed that almost 2/3rds of the 39% difference between young men and women could be attributed to the burden of extra body fat and less fat-free weight, resulting in more total aerobic energy in an average man compared to an average woman. Untrained young adult women have been shown to average about 25% body fat, while young men have been shown to average about 15% body fat (Katch and McArdle, 1993). Based on comparing the percentage difference between men and women with respect to their VO2max and weight adjusted VO2max, this study supports a similar conclusion (close to 2/3rds of differences in VO2max between men and women tend to disappear when weight adjusted VO2max percentage difference is considered). Results of comparison of overall magnitude in VO2max between men and women from this study are also similar to other studies such as MacNab et al. (1969) and Patton et al. (1980). Mamansari and Salokhe (1996) report male– female magnitude differences of about 69% when using weight adjusted VO2max, and 67% when using VO2max (l/min). According to Bhambani and Maikala (2000), men had 37% higher VO2max (l/min) than women, and 22% higher weight adjusted VO2max than women. Lloyd and Cooke

(2000) report about a 15% difference (higher in men) in weight adjusted VO2max. Woo et al. (2001) found that VO2max (l/min) of Korean women was 72% that of Korean males in submaximal treadmill testing. Korean women had 88% of the aerobic capacity of Korean men when weight adjusted VO2max values were compared. Even without regular bouts of physical training, differences in normal physical activity levels between an average male and an average female due to social constraints could result in significant differences in maximal aerobic capacities. Several other studies have also reported values of maximum heart rates when estimating aerobic capacity using submaximal methods with young adults. Table 7 presents results from studies considered for comparison in this work. A comparison of the overall magnitude of maximal heart rates indicates that young women in this study had higher maximal heart rates than other populations. Results from this study also validate the relationship between heart rate and ratings of perceived exertion of participants. At each workload stage, the heart rate is approximately ten times the rating of perceived exertion at that stage. Several factors may have affected accurate assessment (particularly, an overestimation) of aerobic capacity in this study. Assessment of VO2max requires recruitment of large muscle groups in the body, and an exercise intensity and duration that is sufficient to maximize aerobic energy transfer. Studies have shown that even with maximal exercise testing protocols, having individuals, especially untrained individuals such as those who participated in this study, reach acceptable levels of oxygen consumption for estimation of peak values, is often difficult and requires considerable prodding of participants (Vogel et al., 1986; McArdle et al., 2001). McArdle et al. (2001) provided a second treadmill test immediately after a first treadmill administration where participants believed they had been pushed to their maximal levels. They found that the aerobic capacity estimated from the second test was significantly higher (by more than 1.4%) after the second test compared to the first.

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Table 7 Maximum heart rates (beats/minute) when estimating aerobic capacity Study

This study

Vogel et al. (1986)

Jackson et al. (1994) Bhambhani and Maikala (2000)

Estimation method

Sub maximal method; 214-0.71 (Age) Maximal testing and recording of heart rate Maximal testing and recording of heart rate Maximal testing and recording of heart rate

Since the quantity of muscle mass activated during exercise has been shown to affect maximal aerobic capacity (Blomqvist et al., 1981; Lewis et al., 1983), the test protocol (whether continuous protocol or interrupted, whether maximal or whether estimated from submaximal methods such as from extrapolation from maximal predicted heart rate), and the method used (bicycle ergometer, graded treadmill exercise, etc) in assessment of aerobic capacity has been shown to be a factor in affecting estimates of aerobic capacity, especially for purposes of comparisons among populations (Hermansen and Saltin, 1969; McArdle and Magel, 1970; Shephard et al., 1968; McArdle et al., 2001). McArdle et al. (1973) and Duncan et al. (1997), for example, reported similar values of maximal oxygen consumption for both continuous and discontinuous (with time for recovery between workload increments) protocols. The largest difference in maximal oxygen consumption between three treadmill running tests in the experiment by McArdle et al. (1973) was only 1.2%. Researchers have compared results of maximal aerobic capacity measured from treadmill testing with various forms of exercise tests such as bench-stepping (Kasch et al., 1966), arm ergometry (Toner et al., 1983), recreational and competitive swimming (Magel and Faulkner, 1967; McArdle et al., 1978), competitive racewalking and running (Menier and Pugh, 1968), and

Exercise type

Maximum heart rate Males

Females

Treadmill

197.13 (n=16, SD=1.75)

197.8 (n=5, SD=0.45)

Treadmill

190.7 (n=210, SD=6.8)

189.8 (n=212, SD=7.4)

Treadmill

187.1 (n=145, SD=8.2)

n/a

Treadmill

190 (n=11, SD=9.6)

182 (n=11, SD=9.3)

competitive cycling (Hagberg et al., 1978). Researchers suggest that a continuous protocol with increments in workload in 15-second intervals may result in accurate assessment of aerobic capacity using treadmill testing (Fairshter et al., 1983). Furthermore, for laboratory-based testing of healthy subjects, treadmill exercise seems to be the recommended approach (McArdle et al., 2001). Other factors such as genetics and family environment have also been shown to affect aerobic capacity of individuals. Researchers currently estimate that genetic effects, together with familial environment, and adjusted to reflect variations in age, gender and body mass/com position, may contribute to explaining up to 50% individual variation in VO2max (Bouchard and Perusse, 1994; Bouchard et al., 1992; Perusse et al., 1989; Gayagay et al., 1998; Maes et al., 1996; Prud’homme et al., 1994; Rivera et al., 1999). Some other factors that influence maximal oxygen consumption include training and age. In this study, only young, college students were selected for participation—exclusion from this study of industrial workers who are older, and who have poor aerobic fitness because of poor fitness training, may have resulted in an overestimate of aerobic capacity. Since the study was cross-sectional in nature, decline in aerobic

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capacities among Mexican Americans with age was not explicitly considered in this research. Body size and composition has been shown to explain as much as 70% of the differences in VO2max among individuals (Wyndham and Heyns, 1969). Although this study quantified differences in VO2max when normalized with respect to body weight and expressed in ml/kg/min, we did not quantify oxygen aerobic capacity adjusted for fat free mass. Expressing aerobic capacity in terms of fat free mass, in addition to estimating adjustments due to variation in muscle mass activated during exercise, has been shown to reduce the between-subject differences in aerobic capacity even further (Washburn and Seals, 1984; Buskirk and Hodgson, 1997; Proctor and Joyner, 1997). When body mass (in kg) was regressed with VO2max of male participants, no statistically significant relationships (linear, quadratic or cubic) were detected. For women participants in this study, however, the linear relationship between body mass and maximum oxygen consumption was significant at the 5% level (p=0.027). Since in this experiment, we predicted VO2max based on extrapolating age predicted maximal heart rate, the predicted VO2max was based on the assumption of a linear relationship between heart rate and oxygen consumption (VO2) when the intensity of the workload was increased from light to heavy using a standard treadmill testing protocol most suitable for testing young adults in a laboratory setting. The assumption of a linear relationship between heart rate and oxygen consumption with increase in exercise intensity has been shown to hold in most cases, particularly during light to moderate exercise activities. However, it has been found that in some subjects, at intense workloads the heart rate-VO2 line curves in a direction that indicates a larger-than-expected increase in oxygen consumption per unit increase in heart rate. In other words, the actual increase in oxygen consumption is more than what is predicted by linear extrapolation of the HR-VO2 line, resulting in an underestimation of VO2max for these subjects. In testing the linearity assumption at the 3 workloads, we found that, for men, when VO2 values were averaged for the 16 men for each workload, and plotted against the corresponding

average heart rates at each workload, the relationship between VO2 (l/min) and heart rate was linear (po0.032). For men, when the average weight adjusted VO2 values for each workload was plotted against the heart rate, again, the linear relationship was significant (p=0.033). On the average, the linear relationship also held for females (p=0.001 for heart rate versus VO2, and p=0.004 for heart rate versus weight adjusted VO2). Although, on the average, the linear relationship between heart rate and VO2 was statistically significant for males and females, when the linear relationship was examined for each individual participant, the authors found that 5 males out of the 16 males had a trend similar to the one presented in Fig. 5. Fig. 5 is a plot between increasing time on the x-axis (also indicating an increase in workload intensity since exercise testing in this study was continuous with an increase in treadmill speed and gradient every 3 min), and heart rate (beats/minute) and VO2 (l/min) on the yaxis for a male participant. It can be seen from Fig. 5 that close to the 7th minute of testing, the lines intersect and the rate of increase of oxygen consumption (expressed in liters/minute) is more than the rate of increase of heart rate. For the same participant, Fig. 6 shows the relationship between increasing heart rate (in beats/min) with increasing time and increasing oxygen

Fig. 5. Heart rate, VO2 and time relationship for absolute VO2 (l/min).

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Fig. 6. Heart rate, VO2 and time relationship for weight adjusted VO2 (ml/kg/min).

consumption, but, this time, the weight adjusted oxygen consumption expressed in ml/kg/min. It can be seen from Fig. 6 that the rate of increase of heart rate and weight adjusted VO2 is almost equal, thereby making prediction by extrapolation of weight adjusted VO2max from age predicted maximal heart rate valid, due to the validity of the linearity relationship between heart rate and weight adjusted VO2. In summary, it was found that 5 out of 16 males violated the linearity assumption when absolute VO2 (l/min) was used. None of the 5 females violated this assumption when VO2 was expressed in absolute terms. None of the males or females violated the linearity relationship assumption when VO2 was adjusted for weight and expressed as ml/kg/min. The estimation of maximum heart rate is also based on an age predicted equation. For individuals of the same age, one standard deviation of the average maximum heart rate is710 beats/ minute (McArdle et al., 2001). Hence, extrapolating the HR-VO2 line of a young adult to 190 beats/ minute overestimates the VO2max of a person whose actual maximum heart rate is 180 beats/ minute. VO2max is underestimated for a person with an actual maximum heart rate of 200 beats/ minute. The exclusion of the age effect (the decrease in maximum heart rate with increase in age) in a cross-sectional evaluation also consistently overestimates VO2max in older adults.

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There is also the assumption of constant exercise economy and mechanical efficiency during exercise for all participants in this study which may have resulted in an inaccurate assessment of aerobic capacity. For a participant with poor exercise economy, due to an elevated heart rate from the added oxygen cost of uneconomical exercise, the submaximal oxygen consumption will increase more than assumed on the basis of estimates of exercise intensity, thereby underestimating this participant’s VO2max. Studies have shown that this variation is about 6% for cycling or walking economy, and about 10% for bench stepping (Thomas et al., 1993). When testing using a treadmill, there may be as much as a 30% reduction in energy cost when participants are allowed to hold on to the treadmill handrails when exercising. It is also accepted that even with very highly standardized, consistent, and strictly supervised exercise testing protocols, there is a day-today variation in heart of about 5 beats/minute on the average, during submaximal exercise (McArdle et al., 2001).

5. Conclusions Based on the overall magnitudes of VO2max and the weight adjusted VO2max for Mexican American university students as determined in this study, the authors can conclude that there is little evidence to suggest that the aerobic capacities of Mexican American young male adults (especially university students) may be any different from other population groups. It is has to be noted, however, that study sample in this research did not include fulltime industrial workers—as a result, the aerobic capacities for male participants in this study may be overestimates of aerobic capacities of typical Mexican industrial workers. This finding is supported by findings from studies such as the Corpus Christi Heart study (Tortolero et al. 1997), that show that Mexican Americans in the industrial worker age groups are prone to greater risk of incidences of cardiovascular diseases compared to other population groups. Therefore, it can be reasonably expected that Mexican American industrial workers would have lower aerobic

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