Comparison of cardiorespiratory responses between treadmill and bicycle ergometer exercise
Article information
Abstract
The talk test (TT) is a subjective, self-administered method used to gauge aerobic exercise intensity based on a person’s ability to speak comfortably during physical activity. This study aimed to validate the TT by examining its relationship with physiological markers collected during cardiopulmonary exercise testing (CPX) on both a treadmill and stationary bicycle in healthy adults. Twenty-two healthy participants (17 males and 5 females), with no known musculoskeletal, cardiovascular, or pulmonary conditions, completed two exercise sessions—one on a treadmill and another on a stationary bicycle. Each session was structured into three stages of increasing intensity based on the TT. During each stage, various psychophysiological and cardiorespiratory variables were measured, including heart rate, rating of perceived exertion, metabolic equivalents, arterial oxygen saturation, respiratory rate, minute ventilation, oxygen uptake, carbon dioxide production, respiratory exchange ratio, and ventilatory threshold. Significant differences were found across the three TT stages for all measured variables, with values increasing linearly as intensity progressed. However, no significant differences were observed between exercise modalities (treadmill vs. bicycle) or in the interaction between TT stages and modality. The findings support the TT as a valid indicator of exercise intensity, correlating well with physiological responses measured during CPX. The consistency across both exercise modalities suggests that TT is a practical, effective tool for guiding aerobic exercise intensity, particularly in clinical and rehabilitation settings.
INTRODUCTION
Exercise training is commonly recommended for patients with cardiovascular disease to improve their physical activity levels and facilitate cardiovascular adaptations (Pelliccia et al., 2021; Sandercock et al., 2013). Although exercise frequency and duration contribute significantly to generating the internal training load necessary for adaptation, appropriate exercise intensity prescription remains a critical factor to ensure an effective training stimulus (Bok et al., 2022; Esteve-Lanao et al., 2005; Impellizzeri et al., 2019; Seiler, 2010). Traditionally, exercise intensity is prescribed based on parameters derived from cardiopulmonary exercise testing (CPX), which provides essential reference points but requires specialized equipment, trained personnel, and may not always be accessible or feasible in various settings. To overcome these barriers, alternative and cost-effective methods such as the Borg Scale and the talk test (TT) have been employed (Reed and Pipe, 2014; Russell, 1997). These accessible tools provide practical and easily applicable methods for prescribing and monitoring aerobic exercise intensity, particularly in home-based programs or circumstances where resources and direct clinical assessments are limited (Vieira et al., 2022).
To evaluate aerobic exercise intensity or prescribe exercise programs, psychophysiological response markers such as heart rate reserve, oxygen uptake reserve, heart rate, metabolic equivalents (METs), and rating of perceived exertion (RPE) have traditionally been used (Woltmann et al., 2015). Additionally, parameters obtained through pulmonary gas exchange analysis, including ventilatory respiratory exchange ratio (PER), minute ventilation (VE), carbon dioxide output, ventilatory threshold (Vt), and respiratory rate (RR), serve as important physiological measures for precise assessment. However, collecting these physiological data typically requires specialized equipment, which may present practical limitations in various environmental contexts. In contrast, subjective methods such as the RPE or TT offer the advantage of simplicity and convenience, enabling the assessment of exercise intensity without complex instrumentation (Ritchie, 2012; Rouse et al., 2021).
TT, initially inspired by a concept introduced by mountain climbers in 1937, has been validated as a simple and effective method for prescribing and monitoring exercise intensity across various populations, including sedentary individuals, trained healthy adults, and cardiac rehabilitation (Nielsen and Vinther, 2016; Saini et al., 2018). TT assesses an individual’s ability to speak comfortably during exercise, classifying exertion levels based on speech comfort, difficulty, or discomfort. TT is recognized as a simple and practical assessment tool, effectively replacing complex measurement methods, for evaluating exercise intensity in patients with chronic respiratory and cardiovascular diseases, as well as in athletes and the general population (Quinn and Coons, 2011; Rodríguez-Marroyo et al., 2013).
During aerobic exercise, physiological response markers provide critical information necessary for assessing exercise intensity and prescribing appropriate exercise programs. TT remains relatively unfamiliar within respiratory and cardiac rehabilitation settings. In clinical practice, subjective clinical assessments exist for patients with respiratory and cardiovascular diseases, and most evaluations rely on objective physiological markers obtained through specialized instrumentation. On the other hand, treadmill and stationary bicycle exercises are commonly used aerobic exercise modalities for indoor training. Several previous studies have compared these two modalities, highlighting their ability to effectively enhance cardiorespiratory function while maintaining relatively low perceived exertion (Abiodun et al., 2015; Nielsen and Vinther, 2016; Rodríguez-Marroyo et al., 2013). Therefore, the present study aims to investigate and compare physiological and perceptual responses at various exercise intensities using TT between these two aerobic exercise modalities, treadmill and stationary bicycle.
MATERIALS AND METHODS
Participants
Total 22 healthy individuals (17 men, 5 women) from local colleges and universities participated in the study. Participants were selected based on the following inclusion criteria: (a) absence of any known history of cardiovascular or pulmonary diseases, (b) capability of performing everyday activities without limitations, (c) no abnormalities in posture or walking ability, (d) refrained from alcohol intake for at least 24 hr prior to testing, and (e) suitability for performing maximal cardiopulmonary exercise testing according to guidelines set by the American Thoracic Society. All participants received detailed explanations regarding the study’s objectives and procedures and voluntarily provided written informed consent prior to their involvement. The study protocol adhered to the ethical guidelines outlined in the Declaration of Helsinki and was approved by the Institutional Review Board of Yeungnam University College (YNC IRB/201904-04).
Respiratory gas analysis
All assessments were conducted using an automatic treadmill system with a breath-by-breath respiratory gas analyzer (Quinton Q-stress system, Baxter, Deerfield, IL, USA). The physiological and respiratory variables measured included heart rate (HR), RPE, METs, arterial oxygen saturation (SaO2), RR, VE, relative oxygen uptake (VO2/kg), carbon dioxide production (VCO2), RER, and Vt. These variables were collected to evaluate exercise intensity across different phases of TT, specifically at baseline (resting phase) and during each TT stage (I, II, III). The experimental sessions were consistently conducted between 4:00 p.m. and 6:00 p.m. in a controlled laboratory environment (temperature range, 20°C–25°C; humidity, 50%–55%). To minimize fatigue-related effects, each participant had a minimum rest interval of 48 hr prior to the second test session.
TT procedure
Participants were requested to avoid any physical exercise for at least 24 hr before the testing sessions. During the exercise sessions, each participant simultaneously recited the “Pledge of Allegiance” while performing exercises on a treadmill and stationary bicycle. After recitation, participants were asked to indicate whether they experienced difficulty speaking comfortably. Both treadmill and bicycle protocols were conducted using a modified Bruce Protocol. A RER exceeding 1.10 was considered indicative of participants achieving maximal exertion. The treadmill and stationary bicycle tests employing TT were conducted in random order on different days at the same time, separated by at least 2 days, to minimize potential learning effects.
During TT, participants were required to engage in conversation while performing treadmill and stationary bicycle exercises. At the final stage of each exercise protocol, participants recited the “Pledge of Allegiance” aloud and then responded with “yes” or “no” to indicate whether they could speak comfortably. TT comprised three incremental stages based on speech difficulty: stage I (comfortable speaking), stage II (speaking possible but somewhat difficult), and stage III (very difficult to speak or RPE score ≥15). The exercise protocol concluded upon reaching stage 3.
The treadmill protocol began with participants walking at a self-selected comfortable speed with a 0% incline for 4 min. Subsequently, the incline was increased by 2% increments every 2 min. The stationary bicycle protocol began with an initial workload of 30 W, and participants cycled at a comfortable pace for 4 min, similar to the treadmill protocol. Subsequently, workload intensity was increased by 30-W increments every 2 min. Upon completion of each exercise stage, participants recited the “Pledge of Allegiance,” after which the examiner assessed their comfort level in speaking. Exercise intensity was then adjusted according to the participants’ verbal responses regarding their ease of speech.
Statistical analysis
Two-way repeated measures analysis of variance (ANOVA) was performed to analyze differences in HR, RPE, METs, SaO2, RR, VE, VO2/kg VCO2, RER, and Vt between resting phase and the three stages of TT (between-group) across the two aerobic exercise modes (treadmill vs. stationary bicycle). Exercise type was assigned as the between-group factor, while TT stage was designated as the within-group factor. Physiological response markers were set as dependent variables. Bonferroni test were conducted for post-hoc analysis to compare dependent variables between the treadmill and stationary bicycle groups at each TT stage. Additionally, Pearson correlation analysis was performed to evaluate the correlation of TT with all dependent variables in the two exercise conditions. All statistical analyses were conducted using IBM SPSS Statistics ver. 27.0 (IBM Co.), with the statistical significance level set at α=0.05.
RESULTS
Participant demographics
Table 1 summarizes participants’ demographic characteristics, including gender, age, height, weight, and body mass index (BMI). Participants had a mean age of 26.64±2.68 years, height of 171.41±7.27 cm, weight of 72.91±13.20 kg, and a BMI of 24.63±3.18 kg/m2.
The general characteristics of the subjects
Differences in physiological responses across TT stages and exercise modalities
In Table 2, repeated measures ANOVA revealed statistically significant within-group differences across all TT stages (P<0.001) in most variables, including HR, RPE, METs, VO2/kg, VCO2, RR, VE, and Vt, in both treadmill and bicycle conditions. However, between-group comparisons showed significant differences only in METs (P=0.041), VO2/kg (P=0.040), and RER (P=0.045), with no significant group×stage interaction observed for any variable (P>0.05). Notably, SaO2 did not differ significantly between exercise modes or across stages, although a small but significant within-group effect was found (P=0.004).
Psycho- and ventilatory-physiological responses under two conditions across the resting phase and three task difficulty levels
Physiological changes from resting phase to TT stages
Table 3 indicates that repeated measures ANOVA revealed statistically significant differences (P<0.001) across all stages of TT when compared to the resting phase in most physiological and psychophysiological variables, including HR, RPE, METs, VO2/kg, VCO2, VE, and Vt, for both treadmill and bicycle conditions. However, no significant differences were observed in SaO2 and RER at lower stages, with RER showing a significant change only at stage III in the treadmill condition (P=0.000) and at stage II in the bicycle condition (P=0.045). RR showed a delayed but significant response at stage III in both exercise modalities.
Statistic results of comparison between the resting phase before the talk test (TT) and the stages of the TT
Correlation between TT stages and exercise intensity markers
Correlation analysis under the stationary bicycle condition revealed significantly strong correlations among most variables, including HR (r=0.869, P<0.001), RPE (r=0.920, P<0.001), METs (r=0.849, P<0.001), VE (r=0.786, P<0.001), VO2/kg (r=0.849, P<0.001), VCO2 (r=0.757, P<0.001), and Vt (r= 0.869, P<0.001). Except for SaO2 (r=0.869, P>0.001), RER (r=0.291, P>0.001), and RR (r=0.374, P>0.001), correlation analyses for the treadmill condition showed statistically significant strong correlations for the majority of measured variables. Specifically, HR (r=0.869, P<0.001), RPE (r=0.920, P<0.001), METs (r=0.893, P<0.001), VE (r=0.771, P<0.001), VO2/kg (r=0.893, P<0.001), VCO2 (r=0.802, P<0.001), and Vt (r=0.896, P<0.001), demonstrated strong correlations. Conversely, SaO2 (r=0.212, P> 0.001), RER (r=0.091, P>0.001), and RR (r=0.408, P<0.001) did not show statistically significant correlations (Fig. 1).
Psycho- and ventilatory-physiological data during rest and three stages of talk test during bicycle and treadmill exercises. HR, heart rate; RPE, rating of perceived exertion; METs, metabolic equivalents; SaO2, arterial oxygen saturation; RR, respiratory rate; VE, minute ventilation; VO2/kg, relative oxygen uptake; VCO2, carbon dioxide output; RER, respiratory exchange ratio; Vt, ventilatory threshold; RP, resting phase before talk test; TT, talk test.
DISCUSSION
The purpose of this study was to examine the validity of TT as a measure of aerobic exercise intensity and to investigate whether differences exist in physiological response markers between treadmill and stationary bicycle exercises, the two most common modalities used for indoor aerobic exercise. In the current study, we measured a variety of physiological variables during cardiopulmonary exercise testing with a treadmill and stationary bicycle and in young adults using HR, psychophysiological response (RPE, METs), and ventilatory gas exchange parameters (SaO2, RR, VE, VO2/kg VCO2, RER, and Vt).
In the comparison of between-subjects results, no significant differences were observed between treadmill and stationary bicycle exercises across all variables according to aerobic exercise intensity, except for METs, VO2/kg, and RER. Additionally, analysis of the interaction effect between exercise modality and TT stage revealed no statistically significant differences in any of the dependent variables. These findings reinforce the clinical applicability of TT as a reliable indicator of exercise intensity. The consistent and significant changes in physiological and psychophysiological markers across each TT stage, compared to the pre-exercise resting state, highlight its potential as a practical and accessible tool for exercise prescription. Given its strong association with cardiovascular and pulmonary load, TT may serve as a feasible alternative to more complex assessments in diverse populations, ranging from healthy individuals to athletes and those with cardiopulmonary conditions. However, no significant differences were observed in cardiovascular responses, pulmonary gas exchange parameters, or psychophysiological indicators between the bicycle and treadmill exercise modalities, suggesting that both forms of aerobic exercise elicit comparable levels of exercise intensity.
TT is a simple, non-invasive method for estimating aerobic exercise intensity by assessing speech comfort under metabolic stress (Althoff et al., 2023; Menezes et al., 2023; Reed and Pipe, 2014). It reflects the interplay between respiratory demand and phonation, and previous studies have shown that TT stages correspond well with ventilatory and psychophysiological responses observed during cardiopulmonary exercise testing, regardless of the speech provocation method used (Forbregd et al., 2019; Meckel et al., 2002). TT has been applied in various populations, including athletes, individuals with obesity, cancer, and cardiovascular disease, and is currently recommended in cardiovascular disease guidelines despite the lack of a standardized protocol of pulmonary disease (Aabo et al., 2021; Gillespie et al., 2015; Rodríguez-Marroyo et al., 2013). This increased interest and usefulness of TT as an evaluation and prescription tool for patients with cardiopulmonary diseases calls for further knowledge about its applicability, protocols, and properties (Vieira et al., 2022). Among the key elements of exercise prescription—frequency, intensity, time, and type—intensity is often regarded as the most critical for achieving desired physiological benefits. The TT offers a practical alternative for guiding exercise intensity and may support both individualized prescription and self-monitoring within the recommended target zones (Reed and Pipe, 2014; Saini et al., 2018).
In the current research, we examined several psychophysiological and ergospirometric indicators reflecting the cardiovascular and respiratory status of participants. Many previous investigations employing cardiopulmonary exercise testing have demonstrated the usefulness of objective physiological measurements—such as HR, respiratory gas exchange parameters, METs, and ratings of perceived exertion—for accurately monitoring physiological status and guiding exercise prescriptions (Abell et al., 2017; Kwon et al., 2023; Panza et al., 2024; Reed and Pipe, 2016; Saini et al., 2018). HR has a linear relationship with VO2, regulated by the autonomic nervous system. VO2 and VCO2 reflect respiratory gas exchange during exercise (Kwon et al., 2023). RPE is a subjective, practical tool for exercise intensity prescription. METs standardize exercise intensity relative to resting metabolism, while SaO2 reflects pulmonary gas exchange efficiency (Saini et al., 2018). During low- intensity exercise, increases in RR and VE primarily reflect the achievement of the Vt. The RER, representing metabolic energy expenditure, is determined by the ratio between VCO2 and VO2. VE refers specifically to the total volume of air expired from the lungs per minute (Kwon et al., 2023). Physiologically, speech comfort during exercise typically corresponds to intensities below the Vt, beyond which lactate accumulation and increased CO2 pressure stimulate ventilation, disrupting speech ease (Quinn and Coons, 2011; Saini et al., 2018). TT demonstrates high reliability (Intraclass correlation coefficient ≥0.80), comparable to HR monitoring and superior to perceived exertion ratings, and serves as a validated proxy for Vt or lactate threshold (LT), even in patients on beta-blockers (Mezzani et al., 2013; Vieira et al., 2022; Zanettini et al., 2013). Exercising at or slightly below a comfortable speech intensity (3–<6 METs) aligns with American College of Sports Medicine recommendations and is considered safe, remaining below ischemic thresholds, thus supporting the clinical utility of TT in cardiovascular disease prevention and rehabilitation.
The comparison between aerobic exercise modalities using treadmill and stationary bicycle demonstrated no statistically significant differences across all dependent variables during each stage of TT, except for METs, VO2/kg, and RER. A possible explanation for the lack of statistical significance may be attributed to insufficient sensitivity of cardiopulmonary and psychophysiological measurements in distinguishing between the two exercise modalities at various intensities (rest, comfortable speaking, somewhat difficult speaking, and very difficult speaking). Additionally, the small sample size might have limited the statistical power and generalizability of these findings. However, the treadmill consistently elicited greater cardiovascular and respiratory metabolic responses at all exercise intensities compared to the bicycle, although the RER showed the opposite trend. Our results are consistent with those reported by Abrantes et al. (2012) and Tomas et al. (1989), who suggested that higher RER values observed during cycling may be related to increased blood lactate accumulation. This phenomenon likely occurs because cycling, as a non–weight-bearing exercise modality, mobilizes less overall muscle mass and relies more heavily on glycolytic muscle fibers.
Several prior studies have reported differences in physiological responses, such as blood pressure, HR, maximal oxygen uptake, and lactate accumulation, depending on the type of aerobic exercise modality (treadmill vs. bicycle), each method offering distinct physiological advantages (Coyle et al., 1991; Hsia et al., 2009; Jacobs and Sjodin, 1985; Kravitz et al., 1997; Scott et al., 2006). Hsia et al. (2009) reported higher blood pressure and HR during treadmill exercise compared to cycling, while Kravitz et al. (1997) found higher energy expenditure and maximal oxygen uptake with treadmill use. Abrantes et al. (2012) suggested that the current findings suggest that treadmill exercise elicits greater cardiopulmonary responses, such as higher VO2 and HR, compared to cycling at similar intensities.
Collectively, previous findings suggest that treadmill exercise has higher discriminative capacity for assessing exercise intensity and induces greater cardiovascular and metabolic demands compared to stationary bicycle exercise (Abrantes et al., 2012; Kravitz et al., 1997; Saini et al., 2018). This difference may be explained by the broader activation of upper and lower extremity and trunk muscles during treadmill exercise, resulting in higher overall aerobic activity. With the rising prevalence of cardiovascular and pulmonary diseases and the growing social demand for comprehensive healthcare services, there is an increasing need for effective evaluation and treatment strategies in the fields of cardiac and pulmonary rehabilitation. Acquiring the knowledge and skills to assess patients’ respiratory patterns and psychophysiological responses according to varying levels of exercise intensity has become essential. Although several objective methods for assessing exercise intensity have already been validated in clinical practice, there remains a need for tools that are simple, rapid, and feasible in real-world clinical settings. TT offers such an alternative, providing an accessible means of estimating exercise intensity without requiring complex or costly equipment. Numerous previous studies have demonstrated the reliability and validity of TT, supporting its use across various populations and clinical contexts (Kwon et al., 2023; Mahmod et al., 2022; Saini et al., 2018; Vieira et al., 2022).
While this study did not identify statistically significant differences in psychophysiological responses between treadmill and bicycle exercises, TT showed strong correlations with established measures of exercise intensity, and the physiological responses observed were consistent with the expected intensity levels. Future studies with larger sample sizes and the inclusion of more objective cardiopulmonary biomarkers may yield more definitive results and help further generalize the findings to broader clinical applications.
Notes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
ACKNOWLEDGMENTS
This study was supported by the Yeungnam University College Research Grants in 2023.