Differences between treadmill and cycle ergometer cardiopulmonary exercise testing results in amateur triathletes and their association with body composition and body mass index

doi:10.21203/rs.3.rs-917362/v1

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Differences between treadmill and cycle ergometer cardiopulmonary exercise testing results in amateur triathletes and their association with body composition and body mass index

https://doi.org/10.21203/rs.3.rs-917362/v1

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published 16 Mar, 2022

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Cardiopulmonary exercise testing (CPET) is the method of choice to assess aerobic fitness. Previous research was ambiguous as to whether treadmill (Tr) and cycle ergometry (CE) results are transferrable or different between testing modalities in triathletes. The aim of this paper was to investigate the differences in HR and VO₂ at maximum exertion and at anaerobic threshold (AT) and respiratory compensation point (RCP) and evaluate their association with body fat (BF), fat free mass (FFM), and body mass index (BMI).

143 adult (n = 18 female), amateur, Caucasian triathletes had both Tr, and CE CPET performed. The male group was divided into < 40 years (n = 80) and > 40years (n = 45). Body composition was measured with bioelectrical impedance before tests. Differences were evaluated using paired T-tests and associations were evaluated in males using multiple linear regression (MLR).

Significant differences were found in VO₂ and HR at maximum exertion, at AT and at RCP between CE and Tr testing, in both males and females. VO_2AT was 38.8(± 4.6) ml/kg/min in Tr vs 32.8(± 5.4) in CE in males and 36.0(± 3.6) vs 32.1(± 3.8) in females (p < 0.001). HR_AT was 149 (± 10) bpm in Tr vs 136 (± 11) in CE in males and 156 (± 7) vs 146 (± 11) in females (p < 0.001). VO₂max was 52 (± 6) ml/kg/min vs 49 (± 7) in CE in males and 45.3 (± 4.9) in Tr vs 43.9 (± 5.2) in females (p < 0.001). HRmax was 183 (± 10) bpm in Tr vs 177 (± 10) in CE in males and 183 (± 9) vs 179 (± 10) in females (p < 0.001). MLR showed that BMI, BF and FFM are significantly associated with differences in HR and VO₂ at maximum, AT and RCP in males aged > 40.

Both tests should be used independently to achieve optimal fitness assessment and further training planning.

Physiology

Cardiac & Cardiovascular Systems

CPET

treadmill (Tr)

cycle ergometry (CE)

body fat (BF)

fat free mass (FFM)

body mass index (BMI)

Cardiopulmonary exercise testing (CPET) is a dynamic, non-invasive method to assess the cardiopulmonary system at rest and during exercise¹. It may be applied in medicine to evaluate the degree of cardiovascular function impairment and plan rehabilitation, and in sport science to assess participants fitness². Key variables measured in CPET include heart rate (HR), oxygen consumption (VO₂), respiratory rate (RR), pulmonary ventilation (VE), oxygen pulse, respiratory exchange ratio (RER), ventilatory equivalents for oxygen (VE/VO₂) and for carbon dioxide (VE/VCO₂) ³. The most frequently compared variable is the maximum oxygen uptake (VO₂max), which may be defined as the highest value reached, despite progressive increase of the load applied, with the development of a plateau in the VO₂³. Another important value is the VO₂ at the anaerobic threshold (AT), corresponding to the threshold between moderate and high intensity exercise, is the point when the lack of sufficient oxygen supply to the exercising muscles necessitates glycolytic ATP production and accumulation of lactic acid ⁴. Thus, in exercise at intensity below AT, lactate remains at resting levels, while in high intensity exercise above _AT, lactate rises until an elevated steady state is attained ⁴. The respiratory compensation point (RCP) is identified as the second breakpoint in the ventilation response and is a measurable variable most closely related to the concept of critical power (CP), which in turn represents the point separating power outputs that can be sustained for a prolonged time from power outputs which lead to a certain maximum after which exercise intolerance occurs ^4,5. CP is especially relevant in high intensity training or intermittent high intensity training ⁵.

The most commonly used testing modalities are the cycle ergometer and treadmill, used with various protocols or self-paced ^6,7. These training modalities both have unique strengths and weaknesses. The treadmill activates more muscle groups and VO₂max is generally higher than in the cycle ergometer by 7–18%, varying between studies, although there exist many conflicting papers and results are inconsistent ⁸. The cycle ergometer allows better electrocardiographic (ECG) analysis due to fewer artifacts from upper body motion and is safer and less intimidating for people unaccustomed with a moving treadmill ⁶.

The relationship between testing modality and VO₂ max is ambiguous. In untrained subjects, VO₂ max is generally higher in treadmill testing. However, athletes with previous experience in cycling may obtain results on the cycle ergometer which are equal to or even higher than those obtained on the treadmill, while trained runners display higher results in treadmill testing ^9,10. Usually for athletes the testing modality is selected specifically to fit the discipline trained by the examinee, i.e. a treadmill for runners or a cycle ergometer for cyclists ¹¹. A unique challenge is posed by triathletes, who have no single mode of training, but rather devote a portion of their training to swimming, cycling and running ⁸. The monitoring of training would therefore ideally be carried out with all of the specific tests for the most accurate results, but this would be highly impractical given that testing is time consuming, costly and must be repeated regularly ¹¹. It is therefore important to know whether there is a significant difference between treadmill and cycle ergometry results in triathletes. Few studies have been conducted to assess this, and existing studies often included small studied groups of fewer than twenty participants ⁸. The results of previous studies are inconclusive, showing that VO₂ max in triathletes may be equal ^12–16, higher ^17,18 or even lower ¹⁹ in treadmill testing compared with cycle ergometry. The anaerobic threshold (AT) and lactate threshold (LT) were also either reported as higher in the treadmill test ²⁰, or similar in both tests ²¹. Millet et al. point out that study methods were often unclear and the study group sizes were limited in many of the existing studies ⁸.

Maximal heart rate (HRmax) is either reported as similar ^14,17,20,22, or slightly higher in treadmill testing compared with cycle ergometry ^19,20,23. It is also unclear whether this relationship is true for males and females alike, or only for males ⁸. Another important parameter to consider is the HR corresponding to the AT, which is often used to prescribe submaximal exercise training loads ⁸. This value has previously been generally reported as higher in treadmill tests compared with cycle ergometry ^{14,19,23−25}. However, some studies yielded no significant difference ^12,26.

The sex differences between triathletes in running and cycling are also unclear. Most studies did not evaluate these differences at all and the ones that did yielded no difference between cycling and running for both males and females ^15,27.

It has been proposed that the difference in VO₂max between treadmill and cycle ergometry varies between runners and triathletes may be due to the higher muscle mass of triathletes, especially in the upper body, and not to running economy ⁸. To the best of our knowledge, no studies evaluated whether an association exists between body composition (BC) and differences in VO₂max in different testing modalities in triathletes.

The main aim of this study was to assess the difference in VO₂ and HR at maximum exertion and at AT and RCP in cycle ergometry and treadmill testing. A further aim was to evaluate whether an association exists between these parameters and BC or body mass index (BMI).

The data of participants was gathered from records of commercial CPET performed in years 2013–2020. They were recruited via internet and social media advertisements, or via recommendation from trainers or other clients. The tests were carried out on personal request of the participants as part of training optimization and diagnostics. The participants were amateur triathletes who had participated in competitive events. Inclusion criteria for the study were: age over 18 years, triathlon training for at least 3 months, having a treadmill test and a cycle ergometer test performed within a maximum 2 months’ timeframe, and meeting the maximum exertion criteria described below. Exclusion criteria were any chronic or acute medical conditions (including musculoskeletal system disorders like new fractures and sprains, as well as addiction to nicotine, alcohol, or other substances) or ongoing intake of any medication. Identical study methods and procedures were used during the entire period from which data were gathered. Participants were informed via e-mail on how to prepare for the test. They were advised to avoid any exercise 2 h prior to the test, eat a light carbohydrate meal 2–3 h before the test and stay hydrated by drinking isotonic beverages. They were also instructed to avoid medicines, caffeine, and cigarettes before the test.

From the database, we obtained 238 individual cases of people who carried out the study twice (cycling and running separately). After verifying the inclusion criteria, we obtained 143 cases included in further analysis. Populational data was calculated as means with standard deviation (SD) and is presented in Table 1. Body mass (BM) and fat mass (FM) were measured with the use of a BC analyzer (Tanita, MC 718, Japan) before every test with the multifrequency 5 kHz/50 kHz/250 kHz electrical bioimpedance method. The BC tests were conducted directly prior to each CPET if the interval between tests was > 48h and mean values from both tests were further analyzed. In cases where two CPET tests were carried out on following days, only one BC analysis was performed prior to the first CPET. All measurements (BC and CPET) took place under similar conditions in the medical clinic Sportslab (www.sportslab.pl, Warsaw, Poland). The conditions were: 40 m² of indoor, air-conditioned space, altitude 100 m MSL, temperature 20–22 degrees Centigrade, 40–60% humidity. Exercise tests were performed on a cycle ergometer Cyclus-2 (RBM elektronik-automation GmbH, Leipzig, Germany) and on a mechanical treadmill (h/p/Cosmos quasar, Germany), within 1day – 2months of one another.

Table 1

Population characteristics for males and females, including characteristics of the age groups ≤ 40 and > 40 years of age in males and the mean differences between them.
Female athletes
Characteristic	All n = 18¹
Age	33 (7)
Height	169 (4)
Weight	61.9 (4.4)
BMI	21.70 (1.37)
BF	23.3 (3.5)
FM	14.55 (2.93)
FFM	47.38 (2.61)
Male athletes
Characteristic	All n = 125	≤ 40, n = 80¹	> 40, n = 45¹	Difference²	95% CI^2,3	p-value²
Age	38 (10)	32 (5)	46 (8)	15.39	12.10–15.67	< 0.001
Height	181 (7)	181.0 (7.0)	180.0 (6.0)	1.40	-1.00, 3.80	0.3
Weight	79 (9)	78.0 (10.0)	79.0 (8.0)	-0.67	-4.00, 2.70	0.7
BMI	24.04 (2.19)	23.8 (2.4)	24.4 (1.7)	-0.56	-1.30, 0.18	0.13
BF	15.4 (4.2)	15.2 (4.2)	15.8 (4.3)	-0.60	-2.20, 1.00	0.5
FM	12.3 (4.6)	12.2 (4.8)	12.6 (4.1)	-0.47	-2.10, 1.10	0.6
FFM	66 (6)	66.0 (6.0)	66.0 (6.0)	-0.21	-2.40, 2.00	0.9
¹ Mean (SD) ² Welch Two Sample t-test ³ CI = Confidence Interval Height (cm); Weight (kg); BMI, body masa index; BF, body fat (%); FM, fat mass (kg); FFM, fat free mass (kg).

During all tests, cardio-pulmonary indices were recorded using a Cosmed Quark CPET device (Rome, Italy), calibrated before each test according to the manufacturer’s instructions. HR was measured using the ANT + chest strap which is part of the Cosmed Quark CPET device (declared accuracy similar to ECG, ± 1 bpm.). Each test was preceded by a 5 min warm up (walking or pedaling with no resistance). To account for different exercise capacity of the athletes, the initial power (Watt) or speed (km/h) were determined based on an interview carried out before each individual test. The lowest power at which the participant subjectively felt resistance was selected as the initial power for cycle ergometer tests (60-150W). The power was then increased by 20–30 W every 2 min. For treadmill tests the start speed was an individually selected slow running pace, between 7 and 12 km/h based on interview and 1% incline was applied. The speed was then increased by 1 km/h every 2 min. To assess the maximum level of aerobic fitness, participants were instructed to maintain the effort for as long as possible, encouraged verbally to the greatest possible effort. They could terminate the test at any moment if they felt they could no longer maintain the exertion level. Participants were under cardiopulmonary monitoring during the entire test. Before each CPET, after each change of load, and 3 minutes after the test, 20 µL of blood were collected from the fingertip for determination of lactate concentration (LA) using the Super GL2 analyzer (Müller Gerätebau GmbH, Freital, Germany) calibrated before each series of samples. There were no interruptions in the CPET during the collection of blood samples. During the running test, the athlete, while running, put his hand on the rail attached to the treadmill and a technician took a blood sample. Before the sample was drawn into the capillary, the first drops of blood were carefully squeezed into a swab. Similarly, during the cycling test, the subject was asked to relax their hands for about 20–30 seconds before the collection, and then the first drops of blood were discarded before taking the sample into a capillary.

The test was terminated by the operator if either VO₂ or HR showed no further increase with increasing speed/power. The results of the BC analysis and CPET were saved as an Excel (Microsoft corporation, Washington, United States) spreadsheet for further analysis. The raw data were anonymized and processed with the use of a custom program created in Python software to identify data at AT, RCP, and maximum exertion. In accordance with current standards, CPET data were recorded breath by breath and then averaged across 15-s intervals; the highest HR in the interval was recoded and HR values were not averaged ²⁸. For statistical evaluation we included only cases where 3 of 4 following criteria were met: RER during test reaching > 1.10, VO₂ plateau (an increase in VO₂ with increasing speed/power lower than 100 ml/min), respiratory frequency over 45/min, perceived exertion over 18 in Borg scale ²⁹. AT and RCP were located from visual inspection. It was assumed that AT was reached after the following criteria were met: (1) VE/VO₂ curve begins to rise with constant VE/VCO₂ curve; (2) End-Tidal Partial Pressure of Oxygen begins to rise with constant End-Tidal Partial Pressure of Carbon Dioxide ³⁰.

It was assumed that RCP was reached after the following criteria were met: (1) a decrease in PetCO₂ after reaching maximal level; (2) a rapid nonlinear increase in VE (second deflection); (3) the VE/VCO₂ ratio reached a minimum and began to increase; (4) a nonlinear increase in VCO₂ versus VO₂ (departure from linearity) ³⁰.

Retrospective performance data

Competition experience was assessed using the enduhub.com database (Enduhub Corporation, Newark, DE). It is a commonly available website where official scores of participants’ competitions on standardized distances (1/8, 1/4, 1/2 Ironman, Sprinter and Olympic distances of triathlon were included) are uploaded by event organizers. Each score in this database is thoroughly validated by professional companies specialized in time measuring during sports events (Datasport, Szczawno Zdrój, Poland and STS-Timing, Łubianka, Poland. Results are verified before publication by enduhub.com editors.

We used the earliest officially available score from distance-standardized triathlon and used it as a starting point to assess competition experience which was presented in months (month of competition and CPET were both included). These times were applied to calculate how long each sportsman is engaged in regular training and actively take part in public competitions.

Ethical considerations

The study involving human participants was reviewed and approved by the Bioethical Committee of the Medical University of Warsaw. The patients/participants provided their written informed consent to participate in this study. All procedures were carried out in accordance with the Declaration of Helsinki.

Data analysis

Statistical analysis has been conducted in R environment/programming language for statistical computing (version 3.6.4) and lmtest and gtsummary libraries ^31,32.

Missing data were identified in lactate values in 7 cases and imputation was performed with random forests ³³.

Normality was tested with the Anderson-Darling test. Data were calculated as means with SD and 95% confidence intervals (CI). Differences between results of both testing modalities were calculated using paired T-tests. A significance level of p < 0.05 was adopted for all results.

MLR models were created to evaluate the relationship between the differences in results from treadmill and cycle ergometry (dependent variables), and body fat (BF), fat free mass (FFM), and BMI. Several regression models were initially tested and MLR was selected as the best fit based on the Akaike information criterion. The models were only created for the male population due to group sizes. The population was also divided according to age into two groups, < 40 years and > 40 years (age was not included as an independent variable in these models). The division was based on the assumption that aerobic capacity decreases rapidly after the age of 40 years in males and is related to muscle mass ^34,35. The Harvey- Collier test was used to test linearity. R-squared (R²) was used to assess the quality of the models.

The differences between CPET results in cycle ergometry and treadmill testing are presented in Table 2 for females and Tables 3–5 for males. Results of MLR are presented in Table 6. Only regression results in the two age subgroups are presented, as no significant relationships were found in the whole male population. All statistically significant results are marked bold. Selected (based on highest R²) relationships are presented as linear regression graphs (Fig. 1).

Table 2

Differences between cycle ergometry (CE) and treadmill (Tr) CPET results in female participants; significant results are bold.
Characteristic	CE, n = 18¹	Tr, n = 18¹	Difference²	95% CI^2,3	p-value²
VO_2AT	32.1 (3.8)	36.0 (3.6)	-3.9	-5.4, -2.5	< 0.001
VO_2ATa	1,976 (257)	2,216 (221)	-240	-328, -152	< 0.001
RER_AT	0.87 (0.05)	0.88 (0.03)	-0.01	-0.04, 0.02	0.5
HR_AT	146 (11)	156 (7)	-10	-14, -6.1	< 0.001
O₂pulse_AT	13.64 (2.07)	14.28 (1.84)	-0.65	-1.2, -0.07	0.031
VE_AT	53 (7)	62 (8)	-8.5	-12, -4.4	< 0.001
RR_AT	29 (5)	36 (8)	-6.7	-9.5, -3.9	< 0.001
Lac_AT	1.77 (0.54)	1.87 (0.46)	-0.11	-0.32, 0.10	0.3
VO_2RCP	40.2 (4.5)	42.9 (4.7)	-2.8	-4.1, -1.4	< 0.001
VO_2RCPa	2,471 (279)	2,642 (283)	-170	-255, -85	< 0.001
VCO_2RCP	2,468 (282)	2,643 (283)	-174	-262, -87	< 0.001
HR_RCP	169 (9)	175 (8)	-6.7	-8.3, -5.1	< 0.001
VE_RCP	80 (10)	86 (9)	-5.3	-11, 0.32	0.063
RR_RCP	38 (6)	44 (7)	-5.7	-7.7, -3.6	< 0.001
O₂pulse_RCP	14.69 (1.80)	15.13 (1.98)	-0.44	-0.82, -0.05	0.029
Lac_RCP	4.30 (0.69)	4.50 (0.82)	-0.20	-0.72, 0.31	0.4
VO₂max	43.9 (5.2)	45.3 (4.9)	-1.4	-2.8, -0.02	0.047
VO₂max_a	2,704 (319)	2,791 (305)	-87	-169, -4.2	0.040
RERmax	1.13 (0.03)	1.11 (0.03)	0.01	-0.01, 0.04	0.3
O₂pulse_max	15.12 (1.96)	15.33 (2.03)	-0.20	-0.59, 0.18	0.3
HRmax	179 (10)	183 (9)	-3.5	-5.2, -1.8	< 0.001
VEmax	110 (18)	104 (13)	6.0	-1.8, 14	0.12
RRmax	55 (11)	55 (9)	-0.11	-2.4, 2.2	> 0.9
Lacmax	10.76 (1.94)	9.40 (1.28)	1.4	0.47, 2.2	0.005
¹ Mean (SD) ² Paired t-test ³ CI = Confidence Interval Abbreviations: VO_2, oxygen uptake; AT, anaerobic threshold; VO_2AT, relative VO₂ at AT (ml/kg/min); VO_2ATa, absolute VO₂ at AT (ml/min); RER_AT, respiratory exchange ratio at AT; HR_AT, heart rate at AT (bpm); O₂pulse_AT, oxygen pulse at AT (ml/beat); VE_AT, pulmonary ventilation at AT (L/min); RR_AT, respiratory rate at AT (breaths per minute); Lac_AT, lactate concentration at AT (mmol/L); RCP, respiratory compensation point; VO_2RCP, relative VO₂ at RCP (ml/kg/min); VO_2RCPa, absolute VO₂ at RCP (ml/min); VCO_2RCP, carbon dioxide production at RCP(ml/min); HR_RCP, heart rate at RCP (bpm); VE_RCP, pulmonary ventilation at RCP(L/min); RR_RCP, respiratory rate at RCP (breaths per minute); O₂pulse_RCP, oxygen pulse at RCP (ml/beat); Lac_RCP, lactate concentration at RCP(mmol/L); VO₂max, relative maximum VO₂ (ml/kg/min); VO₂max_a, absolute maximum VO₂ (ml/min); RERmax, maximal respiratory exchange ratio; O₂pulsemax, maximal oygen pulse (ml/beat); HRmax, maximal heart rate (bpm); VEmax, maximal pulmonary ventilation (L/min); RRmax, maximal respiratory rate (breaths per minute); Lacmax, maximal lactate concentration (mmol/L);

Table 3

Differences between cycle ergometry (CE) and treadmill (Tr) CPET results in male participants; significant results are bold.
Characteristic	CE, n = 125¹	Tr, n = 125¹	Difference²	95% CI^2,3	p-value²
VO_2AT	32.8 (5.4)	38.8 (4.6)	-6.0	-6.7, -5.3	< 0.001
VO_2ATa	2,530 (366)	3,012 (345)	-482	-541, -424	< 0.001
RER_AT	0.86 (0.06)	0.89 (0.04)	-0.02	-0.04, -0.01	< 0.001
HR_AT	136 (11)	149 (10)	-13	-15, -11	< 0.001
O₂pulse_AT	18.73 (2.88)	20.32 (2.36)	-1.6	-1.9, -1.2	< 0.001
VE_AT	66 (10)	83 (11)	-17	-18, -15	< 0.001
RR_AT	28 (5)	37 (8)	-8.2	-9.3, -7.1	< 0.001
Lac_AT	1.70 (0.37)	1.77 (0.40)	-0.07	-0.14, 0.00	0.043
VO_2RCP	44 (8)	48 (6)	-4.1	-5.1, -3.1	< 0.001
VO_2RCPa	3,372 (533)	3,707 (420)	-335	-411, -259	< 0.001
VCO_2RCP	3,378 (539)	3,708 (420)	-329	-406, -252	< 0.001
HR_RCP	163 (10)	172 (9)	-9.4	-11, -8.2	< 0.001
VE_RCP	110 (17)	119 (15)	-9.4	-12, -6.9	< 0.001
RR_RCP	39 (7)	46 (10)	-6.7	-8.1, -5.2	< 0.001
O₂pulse_RCP	20.78 (3.44)	21.59 (2.65)	-0.81	-1.2, -0.39	< 0.001
Lac_RCP	4.21 (0.60)	4.29 (0.74)	-0.08	-0.23, 0.06	0.3
VO₂max	49 (7)	52 (6)	-2.9	-3.6, -2.1	< 0.001
VO₂max_a	3,808 (476)	4,045 (435)	-238	-300, -175	< 0.001
RERmax	1.13 (0.04)	1.11 (0.03)	0.02	0.02, 0.03	< 0.001
O₂pulse_max	21.54 (2.91)	22.16 (2.66)	-0.62	-0.94, -0.29	< 0.001
HRmax	177 (10)	183 (10)	-5.9	-6.8, -5.0	< 0.001
VEmax	158 (24)	152 (18)	6.6	3.4, 9.8	< 0.001
RRmax	57 (10)	58 (10)	-1.8	-3.6, -0.05	0.044
Lacmax	10.93 (1.82)	9.68 (1.65)	1.2	0.91, 1.6	< 0.001
¹ Mean (SD) ² Welch Two Sample t-test ³ CI = Confidence Interval Abbreviations: VO_2, oxygen uptake; AT, anaerobic threshold; VO_2AT, relative VO₂ at AT (ml/kg/min); VO_2ATa, absolute VO₂ at AT (ml/min); RER_AT, respiratory exchange ratio at AT; HR_AT, heart rate at AT (bpm); O₂pulse_AT, oxygen pulse at AT (ml/beat); VE_AT, pulmonary ventilation at AT (L/min); RR_AT, respiratory rate at AT (breaths per minute); Lac_AT, lactate concentration at AT (mmol/L); RCP, respiratory compensation point; VO_2RCP, relative VO₂ at RCP (ml/kg/min); VO_2RCPa, absolute VO₂ at RCP (ml/min); VCO_2RCP, carbon dioxide production at RCP(ml/min); HR_RCP, heart rate at RCP (bpm); VE_RCP, pulmonary ventilation at RCP(L/min); RR_RCP, respiratory rate at RCP (breaths per minute); O₂pulse_RCP, oxygen pulse at RCP (ml/beat); Lac_RCP, lactate concentration at RCP(mmol/L); VO₂max, relative maximum VO₂ (ml/kg/min); VO₂max_a, absolute maximum VO₂ (ml/min); RERmax, maximal respiratory exchange ratio; O₂pulsemax, maximal oygen pulse (ml/beat); HRmax, maximal heart rate (bpm); VEmax, maximal pulmonary ventilation (L/min); RRmax, maximal respiratory rate (breaths per minute); Lacmax, maximal lactate concentration (mmol/L);

Table 4

Differences between cycle ergometry (CE) and treadmill (Tr) CPET results in male participants ≤ 40 years; significant results are bold.
Characteristic	CE, n = 80¹	Tr, n = 80¹	Difference²	95% CI^2,3	p-value²
VO_2AT	34 (6)	40 (5)	-6.2	-7.2, -5.1	< 0.001
VO_2ATa	2,584 (363)	3,078 (350)	-494	-577, -412	< 0.001
RER_AT	0.87 (0.06)	0.88 (0.04)	-0.02	-0.03, 0.00	0.047
HR_AT	140 (11)	151 (10)	-12	-14, -9.5	< 0.001
O₂pulse_AT	18.60 (2.86)	20.40 (2.41)	-1.8	-2.3, -1.3	< 0.001
VE_AT	66 (10)	82 (11)	-17	-19, -14	< 0.001
RR_AT	28 (6)	36 (7)	-8.2	-9.5, -6.9	< 0.001
Lac_AT	1.67 (0.37)	1.76 (0.40)	-0.08	-0.17, 0.00	0.057
VO_2RCP	45 (7)	49 (6)	-4.0	-5.0, -2.9	< 0.001
VO_2RCPa	3,461 (447)	3,790 (417)	-328	-415, -242	< 0.001
VCO_2RCP	3,463 (458)	3,791 (417)	-328	-417, -239	< 0.001
HR_RCP	166 (10)	175 (9)	-8.9	-10, -7.4	< 0.001
VE_RCP	109 (16)	119 (15)	-10	-13, -7.0	< 0.001
RR_RCP	38 (7)	45 (9)	-6.4	-8.0, -4.9	< 0.001
O₂pulse_RCP	20.90 (2.94)	21.71 (2.69)	-0.81	-1.3, -0.36	< 0.001
Lac_RCP	4.15 (0.63)	4.24 (0.72)	-0.08	-0.26, 0.10	0.4
VO₂max	51 (7)	53 (7)	-2.8	-3.8, -1.7	< 0.001
VO₂max_a	3,885 (471)	4,118 (418)	-233	-316, -149	< 0.001
RERmax	1.13 (0.04)	1.11 (0.03)	0.02	0.01, 0.03	< 0.001
O₂pulse_max	21.65 (2.94)	22.22 (2.62)	-0.57	-1.0, -0.14	0.010
HRmax	180 (9)	186 (9)	-5.9	-7.0, -4.8	< 0.001
VEmax	159 (24)	152 (16)	7.3	2.9, 12	0.001
RRmax	56 (11)	58 (8)	-1.3	-3.3, 0.69	0.2
Lacmax	10.94 (1.91)	9.81 (1.53)	1.1	0.59, 1.7	< 0.001
¹ Mean (SD) ² Welch Two Sample t-test ³ CI = Confidence Interval Abbreviations: VO_2, oxygen uptake; AT, anaerobic threshold; VO_2AT, relative VO₂ at AT (ml/kg/min); VO_2ATa, absolute VO₂ at AT (ml/min); RER_AT, respiratory exchange ratio at AT; HR_AT, heart rate at AT (bpm); O₂pulse_AT, oxygen pulse at AT (ml/beat); VE_AT, pulmonary ventilation at AT (L/min); RR_AT, respiratory rate at AT (breaths per minute); Lac_AT, lactate concentration at AT (mmol/L); RCP, respiratory compensation point; VO_2RCP, relative VO₂ at RCP (ml/kg/min); VO_2RCPa, absolute VO₂ at RCP (ml/min); VCO_2RCP, carbon dioxide production at RCP(ml/min); HR_RCP, heart rate at RCP (bpm); VE_RCP, pulmonary ventilation at RCP(L/min); RR_RCP, respiratory rate at RCP (breaths per minute); O₂pulse_RCP, oxygen pulse at RCP (ml/beat); Lac_RCP, lactate concentration at RCP(mmol/L); VO₂max, relative maximum VO₂ (ml/kg/min); VO₂max_a, absolute maximum VO₂ (ml/min); RERmax, maximal respiratory exchange ratio; O₂pulsemax, maximal oygen pulse (ml/beat); HRmax, maximal heart rate (bpm); VEmax, maximal pulmonary ventilation (L/min); RRmax, maximal respiratory rate (breaths per minute); Lacmax, maximal lactate concentration (mmol/L);

Table 5

Differences between cycle ergometry (CE) and treadmill (Tr) CPET results in male participants > 40 years; significant results are bold.
Characteristic	CE, n = 45¹	Tr, n = 45¹	Difference²	95% CI^2,3	p-value²
VO_2AT	31.1 (4.6)	36.9 (3.1)	-5.8	-6.6, -4.9	< 0.001
VO_2ATa	2,434 (354)	2,895 (305)	-461	-532, -390	< 0.001
RER_AT	0.86 (0.05)	0.89 (0.04)	-0.03	-0.05, -0.02	< 0.001
HR_AT	129 (10)	144 (9)	-15	-17, -12	< 0.001
O₂pulse_AT	18.96 (2.93)	20.18 (2.29)	-1.2	-1.7, -0.75	< 0.001
VE_AT	67 (11)	83 (10)	-16	-19, -14	< 0.001
RR_AT	29.1 (4.7)	37.3 (8.4)	-8.2	-10, -6.2	< 0.001
Lac_AT	1.75 (0.36)	1.80 (0.39)	-0.05	-0.16, 0.07	0.4
VO_2RCP	41.1 (8.4)	45.4 (4.3)	-4.3	-6.2, -2.4	< 0.001
VO_2RCPa	3,213 (634)	3,559 (387)	-346	-494, -198	< 0.001
VCO_2RCP	3,228 (637)	3,560 (387)	-332	-481, -182	< 0.001
HR_RCP	157 (9)	167 (8)	-10	-12, -8.3	< 0.001
VE_RCP	112 (19)	119 (16)	-7.8	-12, -3.7	< 0.001
RR_RCP	40 (7)	47 (11)	-7.1	-10, -4.1	< 0.001
O₂pulse_RCP	20.55 (4.21)	21.36 (2.59)	-0.82	-1.7, 0.08	0.073
Lac_RCP	4.31 (0.53)	4.40 (0.78)	-0.09	-0.36, 0.19	0.5
VO₂max	46.9 (6.0)	49.9 (4.8)	-3.0	-4.2, -1.8	< 0.001
VO₂max_a	3,670 (459)	3,916 (439)	-246	-343, -149	< 0.001
RERmax	1.13 (0.03)	1.11 (0.03)	0.03	0.01, 0.04	< 0.001
O₂pulse_max	21.35 (2.88)	22.05 (2.76)	-0.71	-1.2, -0.20	0.008
HRmax	172 (8)	178 (9)	-5.9	-7.5, -4.3	< 0.001
VEmax	157 (25)	151 (22)	5.5	1.0, 9.9	0.018
RRmax	57 (10)	59 (12)	-2.7	-6.6, -4.9	< 0.001
Lacmax	10.90 (1.65)	9.45 (1.82)	1.5	0.72, 2.2	< 0.001
¹ Mean (SD) ² Welch Two Sample t-test ³ CI = Confidence Interval Abbreviations: VO_2, oxygen uptake; AT, anaerobic threshold; VO_2AT, relative VO₂ at AT (ml/kg/min); VO_2ATa, absolute VO₂ at AT (ml/min); RER_AT, respiratory exchange ratio at AT; HR_AT, heart rate at AT (bpm); O₂pulse_AT, oxygen pulse at AT (ml/beat); VE_AT, pulmonary ventilation at AT (L/min); RR_AT, respiratory rate at AT (breaths per minute); Lac_AT, lactate concentration at AT (mmol/L); RCP, respiratory compensation point; VO_2RCP, relative VO₂ at RCP (ml/kg/min); VO_2RCPa, absolute VO₂ at RCP (ml/min); VCO_2RCP, carbon dioxide production at RCP(ml/min); HR_RCP, heart rate at RCP (bpm); VE_RCP, pulmonary ventilation at RCP(L/min); RR_RCP, respiratory rate at RCP (breaths per minute); O₂pulse_RCP, oxygen pulse at RCP (ml/beat); Lac_RCP, lactate concentration at RCP(mmol/L); VO₂max, relative maximum VO₂ (ml/kg/min); VO₂max_a, absolute maximum VO₂ (ml/min); RERmax, maximal respiratory exchange ratio; O₂pulsemax, maximal oygen pulse (ml/beat); HRmax, maximal heart rate (bpm); VEmax, maximal pulmonary ventilation (L/min); RRmax, maximal respiratory rate (breaths per minute); Lacmax, maximal lactate concentration (mmol/L);

Table 6

Regression analysis for males in two subgroups (≤ 40 years and > 40 years).
Age group	≤ 40 years				> 40 years
Predictors	BMI	BF	FFM		BMI		BF		FFM
VO₂AT
b	0.02	0.15		0.01		-0.92		0.39		0.16
95% CI	-0.94, 1.0	-0.33, 0.63		-0.19, 0.22		-1.7, -0.15		0.13, 0.64		-0.03, 0.34
p-value	> 0.9	0.5		> 0.9		0.020		0.004		0.089
R²	0.023				0.197
HRAT
b	0.23	-0.10		-0.06		-1.3		1.0		0.17
95% CI	-1.8, 2.3	-1.1, 0.93		-0.49, 0.38		-3.5, 0.93		0.29, 1.8		-0.36, 0.71
p-value	0.8	0.9		0.8		0.2		0.008		0.5
R²	0.001				0.172
VO₂RCP
b	-0.16	0.30		0.05		-1.4		0.80		0.15
95% CI	-1.1, 0.82	-0.19, 0.80		-0.16, 0.26		-3.1, 0.26		0.24, 1.4		-0.25, 0.56
p-value	0.8	0.2		0.6		0.095		0.006		0.4
R²	0.055				0.169
HRRCP
b	0.47	-0.16		-0.01		-1.3		0.79		0.13
95% CI	-1.0,1.9	-0.89,0.57		-0.32,0.30		-3.0,0.34		0.24, 1.4		-0.27,0.54
p-value	0.5	0.7		> 0.9		0.11		0.006		0.5
R²	0.008				0.035
VO₂max
b	0.35	0.11		0.09		1.3		0.47		0.24
95% CI	-0.60,1.3	-0.37,0.59		-0.29,0.12		-2.4, -0.19		0.11,0.83		-0.03,0.50
p-value	0.5	0.6		0.4		0.022		0.012		0.078
R²	0.054				0.163
HRmax
b	-0.13	0.10	0.12		-1.5		0.78		-0.01
95% CI	-1.1,0.87	-0.40,0.61	-0.09,0.31		-2.8, -0.16		0.35, 1.2		-0.32, 0.30
p-value	0.8	0.7	0.3		0.028		< 0.001		0.9
R²	0.028				0.28
Abbreviations: BMI, body masa index; BF, body fat (%); FFM, fat free mass (kg); VO₂AT, oxygen consumption at anaerobic threshold (ml/kg/min); HRAT, heart rate at anaerobic threshold (bpm); VO2RCP, oxygen consumption at respiratory compensation point(ml/kg/min); HRRCP, heart rate at respiratory compensation point(bpm); VO₂max, maximum oxygen uptake (ml/kg/min); HRmax, maximal heart rate (bpm).

Despite previous research on the topic, it remains unclear whether treadmill and cycle ergometry may be used interchangeably for the monitoring of training in triathletes, largely due to insufficient data on the differences in results obtained from both testing modalities ^8,22,36. In this study we demonstrated significant differences in cardiorespiratory parameters at AT, 2RCP and maximum exertion between cycle ergometry and treadmill testing. Regression models demonstrated significant relationships between BC, BMI and training experience, and the differences in VO₂max in cycle ergometry and treadmill testing, especially in the older population of athletes. To the best of our knowledge, this is the first study to evaluate the differences between treadmill and cycle ergometer CPET in a large group of triathletes and the first to analyse factors associated with these differences.

The results of our study show that both male and female triathletes have a significantly higher VO₂/AT in treadmill than in the cycle ergometer tests. The AT is a crucial parameter in determining performance and in training monitoring in endurance sports, as it indicates the level of exertion an athlete can sustain for a prolonged period of time during competition without rapid lactate build-up ^8,37. Training at the anaerobic threshold (AnT) intensity improves the peak oxygen uptake and the AT level ³⁷. Recent studies also demonstrate that a large volume of low intensity training (i.e. below the AT) is important for endurance athletes ^38,39.

Previous research was ambiguous as to whether VO_2AT differs between testing modalities in triathletes ⁸. This contradicts the results of several previous studies which found no differences in VO₂ at AT, but were conducted on very small groups (14 participants at most) ^{8,13,21,24,40}. Some results were similar to our study ²⁰.The large mean difference in relative VO_2AT of 6ml/kg/min in males shown in our study indicates that the values obtained from both testing modalities likely cannot be used interchangeably. A further factor limiting the interchangeability of results from different testing modalities is the large difference in HR at AT of 13bpm in males and 10bpm in females, which would hinder the accurate prescription of low intensity training based on HR zones. This is contrary to results from the studies of Hue and Bolognesi, who found differences of ~ 7bpm, but without statistical significance, perhaps due to limited numbers of participants^12,26.

We found that the VO_2/RCP was significantly higher in treadmill than in cycle ergometry both in males and females, although the differences were smaller than in the AT. We also found a large and significant difference in HR at RCP of 7-10bpm, again limiting transferability of results between modalities. To the best of our knowledge, no previous study evaluated RCP in triathletes in treadmill and cycle ergometry testing.

The maximum exertion is the most commonly used parameter to assess the aerobic capacity of athletes ⁸. As with the other parameters (VO₂AT, VO₂RCP), we found VO₂max to be significantly higher in treadmill testing than in cycle ergometry. Millet et al. concluded from previous studies that VO₂max is generally similar in treadmill and cycle ergometry testing in triathletes and therefore that triathletes’ training adaptation is similar to that of cyclists ⁸. This is contrary to the results of our study, most likely due to limited sample sizes. In the present study, the differences in AT were larger than at maximum exertion. This may explain why significant differences were observed more often at AT than at maximum. The VO₂ max in our studied population is lower than that reported in most previous studies, probably due to the higher mean age of the participants, which is a known factor limiting VO₂max ^8,29. HRmax was also significantly higher in treadmill testing than in cycle ergometry in both males and females. The results of previous studies on males were conflicting, some indicating HRmax to be lower in cycle ergometry by 6-10bpm ^12,19,20,23 and some finding no significant difference ^{13,14,17,22,41}. Few studies included females and the evidence was also conflicting ^24,42.

We found that the VE was higher in cycle ergometry than on the treadmill, despite a slightly lower ventilation frequency, indicating a higher tidal volume. This is contrary to the lower VE and Vf in cyclists at both AT and RCP. The differences may correspond to higher lactate accumulation and an acidosis-induced respiratory response in cycle ergometry at maximum, but not at AT and RCP, where lactate levels were similar. This is partly similar to the findings of Koyal et al, who described a higher respiratory response due to higher acidosis in cycle ergometry during low, moderate and high intensity of exercise in untrained subjects ⁴³. The differences at low and moderate intensity are most likely due to our subjects’ experience in triathlon training and therefore lower lactate build-up when cycling at submaximal levels, as it has previously been demonstrated that trained cyclists accumulate less lactate in cycle ergometry ¹⁰. The lower VE and Vf in cycle ergometry at AT and RCP is likely due to the lower VO₂.

The variance in differences in VO₂max obtained from treadmill and cycle ergometer testing was significantly explained by BMI, FATP, FFM and training experience in the group > 40 years of age with an R² of 0.25. It has previously been shown that BM and BC are related to aerobic capacity and that the physiological ability to consume oxygen is negatively associated with FM ^44–46. However, to the best of our knowledge, this is the first study to demonstrate an association between BC, BMI, and the differences in treadmill and cycle ergometry CPET results. We hypothesize that this relationship may be caused by the physiological differences between cycling and running. Cycling is a non-weight-bearing activity, with far less eccentric activity than during running ⁴⁷. Therefore, BM and BC may be more important in treadmill testing than in cycle ergometry. It is unclear why the observed differences are better explained by anthropometric variables in the older group compared to the younger group. We may suspect that the difference in the younger population would be better explained by other factors, perhaps by training volume in cycling or running, which were not evaluated in this study. It is also possible that the differences in BC, especially FFM reflect differences in cardiovascular function, which might play a more important role in older athletes and could have different importance in cycle ergometry and in treadmill testing ^48,49.

Differences in HRmax were significantly explained by BMI and FATP in the older population. It has previously been shown that HRmax is related to BC and BMI, but it remains unclear what the cause for this relationship is or why BC is related to the differences in HRmax between treadmill and cycle ergometry ⁵⁰.

VO₂ and HR are higher in treadmill testing at AT, RCP and maximum exertion in both male and female triathletes.

The differences are relatively large, which potentially limits the transferability of treadmill and cycle ergometer testing. For optimal fitness evaluation and training planning, both tests should be carried out in triathletes.

The differences are partly explained by BMI, BF, and FFM in the population above 40 years of age.

The time intervals between tests varied significantly. Tests were carried out at various times of the season. Training data, except months of experience in triathlon, were unavailable. The female group was too small for meaningful regression analysis, but it was larger than in many previous studies and large enough to observe many significant differences. It was not meaningful to divide females into younger and older age groups, as only 2 females were over 40 years of age. BC was measured with bioelectrical impedance, which may be less accurate than some other methods like CT/MRI BC analysis but is commonly used in sports and therefore may be more practically applicable than more advanced methods.

Author contributions

SP, SW, and DŚ: conceptualization and resources. JL, SW, DŚ, and AM: investigation. IC, GG, PK: statistical analysis. SP, SW, GG, PK: writing—original draft preparation. SP, SW, DŚ, PK, GG, JL writing — review and editing. AM: supervision. All authors have read and agreed to the published version of the manuscript

Conflicting interests

SW is the owner of the sportslab clinic. Other authors have no conflict to declare.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Competing interest reported. SW is the owner of the sportslab clinic. Other authors have no conflict to declare.

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Differences between treadmill and cycle ergometer cardiopulmonary exercise testing results in amateur triathletes and their association with body composition and body mass index

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