Revisiting the Achievement of Maximal Effort During Graded Exercise Testing Among Hispanic Children and Adolescents with Obesity

Abstract

Objective:

To evaluate the achievement of maximal effort during graded exercise testing (GXT) using heart rate (HR-max), respiratory exchange ratio (RER-max), and rate of perceived exertion (RPE-max) among Hispanic children and adolescents with obesity.

Methods:

Thirty-two children (18 girls, 14 boys; age: 10–18 years) with obesity completed a GXT on a cycle ergometer. Maximal effort was assessed using multiple HR-max criteria (including 220-age and Tanaka equations), RER-max (≥1.0 and ≥1.1), and RPE-max (≥17). Independent t-tests and regression analyses were used to examine sex differences and associations with physiological variables.

Results:

All participants achieved RPE-max, 94% met the RER-max criterion of ≥1.0, and 53% met ≥1.1. In contrast, only 3.1% met the 220-age HR-max criterion, and fewer than half met any HR-max threshold. HR-max was significantly associated with age but not with resting heart rate or body fat percentage. VO₂max was significantly higher among those who achieved higher HR-max thresholds.

Conclusions:

RER-max and RPE-max are more consistently achieved than HR-max during GXT in Hispanic youth with obesity, suggesting they are more reliable indicators of maximal effort in this population. When RER-max ≥1.0 is attained, maximal effort can be assumed, and the corresponding HR-max may be used to guide individualized exercise prescription for obesity management.

Introduction

Cardiorespiratory fitness (CRF) is associated with lower risk of cardiovascular diseases, less adiposity, and better mental health and academic performance in children and adolescents.¹ The American Heart Association described CRF as an important marker of health in children and adolescents that should be periodically screened to identify those at increased risk of disease.² The gold standard to determine CRF is the measurement of maximal oxygen consumption (VO₂-max) during graded exercise testing (GXT), representing the maximal capacity to absorb, transport, and deliver oxygen for energy production during dynamic exercise.³

Maximal effort (max-effort) during GXT occurs when oxygen consumption does not increase with increases in workload, also known as VO₂ plateau. This criterion is generally not observed in children.^3,4 Therefore, the term VO₂-peak is used instead. However, VO₂-peak could indicate max-effort if other criteria are met during the test, such as, maximal heart rate (HR-max) and maximal respiratory exchange ratio (RER-max). Also, a subjective criterion is the maximal rate of perceived exertion (RPE-max).⁴

It has been suggested that HR-max during childhood and adolescence is independent of age and obesity; remaining at 195 beats per minute (bpm) in tests conducted with cycle-ergometers, and at 200 bpm when using treadmills.^5–6 Also, a mean 197 bpm with 180 bpm as the minimal threshold value for HR-max have been suggested for children and adolescents.⁷ In addition, two popular equations to predict HR-max during maximal exercise testing among children and adolescents are the “220-age” formula and the Tanaka et al. (2001) formula [= 208 − (0.7 × age)].^8–9 Although the applicability of equations to estimate HR-max for children with obesity have been questioned,¹⁰ HR-max estimates among children with obesity using prediction equations have shown similar or lower values compared with children with normal weight.^11–14

RER, determined by the carbon dioxide produced (VCO₂) in relation to the oxygen consumed (VO₂), is another criterion for max-effort during GXT. Resting RER values range between 0.7 and 0.8, and increases with increasing exercise intensity. A 1.1 or higher RER-max criterion has been used in adults, adolescents, and children.^4,15 Studies have also suggested a 1.0 or higher RER-max for children,^3,13,16 but lower RER-max values (=0.98) have been reported among children with a body mass index (BMI) above the 99^th percentile.¹⁷

Children and adolescents are capable of assessing their RPE in relation to their cardiorespiratory and muscular response during GXT.¹⁸ However, at the same relative exercise intensity, children with obesity perceive greater effort than children without obesity.¹⁹ The criteria used to identify the achievement of max-effort during GXT in children and adolescents with obesity is inconsistent, and has not been evaluated among Hispanic children and adolescents with obesity. Therefore, the purpose of this study was to identify the achievement of max-effort during GXT using HR-max, RER-max, and RPE-max in Hispanic children and adolescents with obesity. We hypothesized that Hispanic children and adolescents with obesity will achieve the expected max-effort criteria reported in the literature, and HR-max and RER-max would be age-independent.

Materials and Methods

A cross-sectional study was conducted with Hispanic children and adolescent participants in a multidisciplinary weight control program at the Centro de Diabetes y Endocrinología Pediátrica (CDEP) de Puerto Rico. Children (18 girls and 14 boys) aged between 10 and 18 years, and classified with obesity using a BMI above the 95^th percentile, completed a GXT. The achievement of HR-max criteria was evaluated using previously suggested equations and cutoff values: 220-age equation, Tanaka’s equation, and three predetermined HR-max (≥180 bpm, ≥195 bpm, and ≥200 bpm).^5–9 Also, the achievement of two RER-max criteria (≥1.0 and ≥1.1) was evaluated. A consecutive sampling of participants was conducted from 2021 to 2024 after testing procedures were discussed with parents and children before signing a CDEP informed consent and assent form. Data without personal identifiers were used to conduct the study approved by the IRB of the University of Puerto Rico, Rio Piedras Campus.

All participants performed a GXT using a pediatric cycle ergometer (Ergoselect 100/200, Ergoline GmbH, Bitz, Germany) keeping a cadence of 50 rpm, with 20W increments per minute until volitional fatigue when clinical signs of intense effort were observed. VO₂ (mL/kg·min⁻¹), RER and HR were measured with a Quark CPET system (COSMED, Rome, Italy). RPE was self-reported during the test and immediately postexercise. Body height and weight were measured with a stadiometer (SECA 216) and digital scale (SECA 703), respectively (Seca GmbH &Co. KG., Hamburg, Germany); and BMI (kg/m²) and BMI percentiles were obtained. Bioelectrical impedance (InBody USA, Model 570, Cerritos, California) was used to estimate percent body fat (%fat).

Statistical analysis

An independent t-test was used to test for sex differences. Pearson correlation and regression analyses were conducted to evaluate factors that could influence the achievement of max-effort such as resting heart rate, BMI, and percent body fat as previously suggested.⁷ STATA version 15.0 (StataCorp LLC, College Station, Texas) was used for statistical analyses using an alpha less than 0.05 to establish significance.

Results

Because no significant differences between boys and girls were found, Table 1 includes data for boys and girls combined. Mean age was 14.3 years, BMI was 41.0 kg/m² with all at or above the 99^th percentile, %fat was 49.6%, and waist circumference was 116.4 cm. Mean VO₂-peak was 17.3 mL/kg·min⁻¹, RER-max was 1.13, and HR-max was 172.9 bpm. All participants achieved an RPE indicative of “very, very hard” effort (≥17) with the Borg_6-20 scale.

Table 1.

Descriptive and Cardiorespiratory Characteristics of Study Participants

	Mean ± SD	Median	Range
Age (years)	14.4 ± 2.4	14.5	10–18
Height (cm)	164.7 ± 7.6	164.3	148.5–181.4
Weight (kg)	111.9 ± 25.5	108.9	73.5–199.95
BMI (kg/m²)	41.0 ± 7.4	39.9	31.9–68.8
Waist circumference (cm)	116.4 ± 17.0	113.2	86.3–171.5
Body fat (%)	49.6 ± 5.7	49.9	35.3–59.6
VO₂max (mL/kg·min⁻¹)	17.3 ± 4.0	17.3	8.8–25.7
RER-max	1.13 ± 0.12	1.12	0.90–1.51
HR-max (bpm)	172.9 ± 20.7	176.5	130.0–204.0

VO₂max, maximal oxygen consumption during the graded exercise test; RER-max, maximal respiratory exchange ratio; HR-max, maximal heart rate.

Figure 1 shows the percentage of participants who achieved the criteria for HR-max and RER-max. Most participants were able to achieve the RER-max criteria 1.0 (94%) and 1.1 (53%). Children unable to reach an RER-max of at least 0.98 (1 girl, 1 boy, RER-max: 0.90 and 0.96, age 10 and 17 years) had similar BMI, %fat, and VO₂-peak than the rest of the group. These participants were also unable to achieve any of the HR-max criteria evaluated. Figure 1 also shows that none of the HR-max criteria evaluated reached a high proportion of achievers: 43.8% (14/32) achieved the 180 bpm threshold, 15.6% (5/32) achieved the Tanaka et al. (2001) equation and the predetermined 195 bpm, 12.5% (4/32) achieved the predetermined 200 bpm, and 3.1% (1/32) achieved the 220-age equation.

FIG. 1.

Percent of children and adolescents with obesity who achieved the criteria for maximal heart rate (HR) and maximal respiratory exchange ratio (RER).

The mean VO₂-max, HR-max, and RER-max among achievers and nonachievers of each max-effort criteria is presented in Table 2. Mean VO₂-max was higher (P < 0.05) among those achieving the Tanaka et al. (2001) equation and the predetermined 195 bpm and 200 bpm HR-max criteria. As expected, mean HR-max criteria was higher among achievers compared with nonachievers in all HR-max criteria. However, mean RER-max was not different between those achieving and not achieving the HR-max criteria. Because only one participant achieved the 220-age HR-max criterion, it could not be statistically compared with nonachievers. Moreover, HR-max was not associated with resting heart rate or percent body fat, but it was significantly associated with age (R² = 0.24, P = 0.004).

Table 2.

VO₂max, HR-Max, and RER-Max Among Achievers (Yes) and Nonachievers (no) of HR-Max Criteria

	VO₂max (mL/kg·min⁻¹)		HR-max (bpm)		RER-max
	Yes	No	Yes	No	Yes	No
≥180 bpm	18.7 ± 3.5	16.3 ± 4.2	191.5 ± 8.2^*	158.4 ± 3.5	1.17 ± 0.11	1.11 ± 0.13
≥195 bpm	21.2 ± 2.8^*	16.6 ± 3.8	201.2 ± 1.8^*	167.7 ± 18.1	1.18 ± 0.11	1.13 ± 0.13
≥200 bpm	21.3 ± 3.2^*	16.8 ± 3.9	201.8 ± 1.5^*	168.8 ± 18.7	1.18 ± 0.11	1.13 ± 0.12
220-age	22.7	17.3 ± 4.0	204	171.9 ± 20.2	1.25	1.13 ± 0.12
Tanaka	21.2 ± 2.8^*	16.6 ± 3.8	1.13 ± 0.13^*	167.7 ± 18.1	1.18 ± 0.11	1.13 ± 0.13

P < 0.05 comparing achievers (yes) and nonachievers (no).

Discussion and Conclusions

This study provides new insights into the physiological responses of Hispanic children and adolescents with obesity during GXT, with particular focus on the achievement of max-effort criteria. While no significant sex differences were observed in the attainment of max-effort during GXT, emerging evidence suggests that sex-based physiological differences in peak oxygen consumption may become more pronounced after puberty.²⁰ Consistent with our findings, previous research has reported no sex differences in HR-max and RER-max among trained adolescents, implying that sex does not significantly influence the metabolic processes involved in achieving peak effort.²¹ Our results further demonstrate that although most participants met the RER-max and RPE-max criteria, only a small proportion achieved the commonly used HR-max criterion.

The high rate of RER-max achievement (94% for ≥1.0 and 53% for ≥1.1) supports the use of RER as a reliable indicator of max-effort in this population. These results align with previous studies suggesting that RER-max of ≥1.0 may be more appropriate threshold for children with obesity, particularly given the physiological differences associated with excess adiposity.^4,13,15,17 The consistent attainment of RPE-max (≥17) further reinforces the validity of perceived exertion as a subjective but meaningful measure of effort in pediatric populations.¹⁸

In contrast, the low proportion of participants meeting HR-max criteria, especially the traditional 220-age formula (3.1%), raises questions about the applicability of these thresholds in children with obesity. Even alternative criteria such as ≥180 bpm or the Tanaka equation yielded low achievement rates. These findings suggest that HR-max may not be a reliable standalone indicator of max-effort in this demographic. Potential mechanisms include autonomic dysfunction affecting sympathovagal balance, chronotropic incompetence causing an attenuated HR response to exercise, cardiovascular deconditioning, or psychological factors such as increased perceived exertion, all commonly associated with pediatric obesity.^{12,14,19,22–24}

Interestingly, while HR-max was not associated with resting heart rate or percent body fat, it was significantly correlated with age. This finding contrasts with some prior literature suggesting age-independence of HR-max in youth^6–7 and highlights the need for further investigation into age-related cardiovascular responses in children with obesity.

The observed mean VO₂max (17.3 mL/kg·min⁻¹) was lower than values typically reported in pediatric exercise testing, suggesting a generally low level of CRF in our sample.^4,17,20 This may reflect the sedentary lifestyle and cardiovascular deconditioning often seen in children with obesity, which could also contribute to the limited achievement of HR-max.

This study is among the first to examine max-effort criteria in Hispanic youth with obesity, a population that remains underrepresented in exercise physiology research. While the relatively small sample (n = 32) limits generalizability, the findings offer valuable guidance for clinicians and researchers. Specifically, they suggest that RER-max (≥1.0) and RPE-max (≥17) are more attainable and reliable indicators of max-effort than HR-max in this group.

In conclusion, our results indicate that HR-max criteria are rarely achieved during GXT in Hispanic children and adolescents with obesity, whereas RER-max and RPE-max are more consistently met. These findings support the use of RER-max and RPE-max as primary indicators of max-effort in this population. When these criteria are satisfied, the corresponding HR-max values may still be useful for individualized exercise prescription aimed at obesity prevention and management.

Footnotes

Authors’ Contributions

F.A.R-M. and G.V.-R.: Conceived the study, carried out evaluations, and analyzed data. All authors were involved in writing the article and had final approval of the submitted and published versions.

Author Disclosure Statement

The authors have no conflicts of interest to declare.

Funding Information

No funding was received for this article.

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