VO2max Test of Unhealthy Participants: Comparison
Please note this is a comparison between Version 2 by Bruce Ren and Version 1 by Todd Astorino.

Maximal oxygen uptake (VO2max) is strongly associated with endurance performance as well as health risk. Despite the fact that VO2max has been measured in exercise physiology for over a century, robust procedures to ensure that VO2max is attained at the end of graded exercise testing (GXT) do not exist. This shortcoming led to development of an additional bout referred to as a verification test (VER) completed after incremental exercise or on the following day. 

  • verification testing
  • maximal oxygen uptake
  • unhealthy adults
  • graded exercise testing
  • VO2max criteria

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1. Introduction

Maximal oxygen uptake (VO2max) as determined by the Fick Equation represents the maximal ability of the cardiovascular system to transport oxygen and the capacity of the periphery to extract oxygen to support aerobic metabolism. It is apparent that VO2max is related to endurance performance and, more importantly, premature mortality [1]. Because of this link between VO2max and health status, the American College of Sports Medicine [2] recommends 150 min/week of moderate intensity continuous exercise or 75 min/week of vigorous exercise to enhance fitness and improve overall health status, although attainment of this guideline in U. S. adults is relatively low [3].
Despite the fact that VO2max has been measured in laboratory and clinical settings for a century, there is no standardized exercise testing protocol to assess it as the specific work rate increment, stage duration, and gas exchange sampling interval vary across studies. In addition, there is no robust approach to ensure that VO2max is attained at the end of incremental exercise which is problematic when this value is used to prescribe exercise, assess training responsiveness, or describe health status. In turn, relying on an imprecise estimate of VO2max can have negative effects upon the accuracy of these applications which can change the course of decision making made by practitioners or scientists regarding client health. Various primary (oxygen plateau) and secondary criteria (maximal values of heart rate, respiratory exchange ratio, rating of perceived exertion, and blood lactate concentration) are widely used in this capacity, yet each has its limitations (for additional information on this, please consult Schaun et al. [4]) that may make them ineffective in ensuring that VO2max is actually attained by each participant.
Implementation of a second exercise test completed after the incremental test was first identified by Thoden et al. [5] in active adults who required an ‘exhaustive test’ to be performed after the incremental protocol. Later work [6,7][6][7] showed that completion of this subsequent higher intensity bout (called the verification test (VER)), performed a few minutes or up to 1 week after the incremental exercise bout, led to similar mean estimates of VO2max, thus confirming a plateau in oxygen uptake and, in turn, attainment of VO2max. For example, in 16 distance runners, data [8] showed that 26 of 32 VO2max tests performed on a treadmill reveal similar (≤2% different) estimates of VO2max between ramp and subsequent verification testing. In seven healthy men, Rossiter et al. [9] demonstrated that VER at 95 or 105%of peak power output (PPO) performed 5 min after ramp exercise elicits similar values of VO2max, leading these authors to recommend either protocol as a suitable way to confirm VO2max attainment. Overall, these data show that VER is a robust procedure to confirm attainment of VO2max in healthy active adults.
Despite these data, a valid concern of VER is that its supramaximal effort would be inappropriate for those who are inactive or at risk for chronic disease who lack the exercise capacity due to aging, presence of comorbidities, or desire to sustain such demanding efforts long enough to allow VO2 to attain a maximal value. However, results from inactive adults [10], older adults [11], and those with obesity [12,13,14][12][13][14] demonstrate that it is well-tolerated and feasible in these populations and leads to similar estimates of VO2max as the ramp test. In addition, data show its efficacy to confirm attainment of VO2max in adults with metabolic syndrome [15] as well as heart failure [16]. Recent data also show that implementing VER reveals more precise determinants of increases in VO2max in response to high intensity interval training in adults with metabolic syndrome compared to graded exercise testing [17]. So, similar to healthy adults, use of VER seems warranted to confirm attainment of ‘true’ VO2max in persons with chronic disease.
A recent systematic review [18] summarized data concerning efficacy of VER in healthy participants and concluded that this is a robust approach to confirm the value acquired from incremental exercise. However, having a more accurate estimate of ‘true’ VO2max in this active population may not be that important as their cardiorespiratory fitness is superior, leading to enhanced health status versus less fit populations. In response to exercise training, an increase in VO2max as low as 1.5 mL/kg/min has been identified as being clinically significant in persons with chronic disease [19]. Thus, in persons having low VO2max and, in turn, diminished health status, any small inaccuracies in VO2max assessment may elicit different responses to training and/or inaccurate diagnoses that may modify choice of various treatment options implemented to improve individual health status. In addition, VO2max is frequently measured as a primary outcome in exercise training studies due to its strong relationship with health status [1]. Moreno-Cabanas et al. [17] concluded that ramp testing misrepresents the training-induced change in VO2max in a majority of individuals with metabolic syndrome, and they emphasized the necessity of VER to better represent the VO2max response to training. However, to our knowledge, no review article has summarized efficacy of VER to confirm VO2max incidence in unhealthy participants. Some studies show that VER leads to similar estimates of VO2max versus graded exercise testing, whereas others show significantly higher VO2max when VER is performed. These equivocal findings may cloud judgment as to whether this additional test should be performed to elicit a ‘true’ VO2max and merit development of a review article to provide a thorough overview of feasibility of VER in clinical populations.

2. Methods Used to Assess VO2max during Incremental and Verification Testing

Table 1 denotes the methods used to assess VO2max from graded exercise testing and the subsequent verification test. Fourteen studies utilized primary (VO2 plateau) and secondary criteria (RERmax, HRmax, RPE, and/or blood lactate concentration) to verify attainment of VO2max from GXT, although five studies did not report that any VO2max criteria were used. Cycling was the modality used in 14 of 19 studies, with 1 study employing arm ergometry [23][20] and 4 studies using treadmill exercise in overweight to obese adults [12], adults with hypertension [22][21], athletes with spinal cord injury [24][22], and children with spina bifida [25][23]. The most widely used protocol to assess VO2max during GXT was a traditional ramp test (n = 10 studies), although in nine studies, a step incremental test was used. Studies were characterized by various intervals between protocols, with durations as brief as four minutes to as long as a few hours between tests. Two studies required VER to be performed 24–48 h after completion of GXT.
Table 1. Methodological traits of exercise testing of studies included in this review.
Study Exercise Mode Traditional VO2max Criteria Adopted VO2max Protocol Recovery Phase Protocol VER Protocol VER vs. GXT

Arad et al. [24][22] CE VO2 plateau;

RER ≥ 1.10;

≥95% HRmax
RAMP 4 min

unloaded cycling + 1 W/3 s for women

1 W/4 s for men
10 min active

recovery at 25 W + 2–3 min passive
100% PPO NR
Astorino et al. [9] CE NR STEP

14 W/min for women

21 W/min for men and 5 W/20 s for women and 10 W/20 s for men
1–1.5 h or 24 h later 2-min WU at 28 W for women, 42 W for men followed by

cycling at 105 or 115% PPO
Astorino et al. [23][20]
[5][9][10][11][12][13][20][22][23][26][25][31][29] revealed no significant difference in mean VO2max between protocols, although in 7 of these studies [9[9][10][12][13][23][26][25],10,12,13,25,28,29], individual participants revealed meaningfully higher VO2max (≥3% higher) with VER compared to GXT. Nevertheless, in six studies [14,22,26,27,31,32][14][21][27][32][28][24] the VER-derived VO2max was significantly higher than GXT, with participants’ VO2max ranging from 19–40 mL/kg/min. In one study in cancer patients [21][30], VER-derived VO2max was significantly lower than from GXT.
Table 2. Results from studies included in this review.
Study VO2max GXT

GXT Duration (min) VO2max VER

VER Duration (min) HRmax GXT (b/min) HRmax VER (b/min) Results
Arad et al. [27][32] 28 ± 6 9.6 ± 1.6 30 ± 7 * 2.6 ± 0.5 170 ± 12 172 ± 9 VER elicited a higher VO2peak versus GXT, although there was no difference in HRpeak.
Astorino et al. [9] 32 ± 4 10.5 ± 1.6 32 ± 5 2.7 ± 0.7 191 ± 9 * 187 ± 10 There was no difference in VO2max between protocols, yet several participants demonstrated a higher VO2max in response to VER. GXT revealed a higher HRmax versus VER.
Astorino et al. [23][20]2 17 ± 4 SCI

24 ± 4 AB plateau using individual ΔVO2

values for each

RAMP 7.4 ± 1.4

5 min warm-up + 3 W/min for TETRA, 13 W/min for PARA, and 8–20 W/min for AB
10 min active recovery at 7 W 2 min at 7 W + arm cycling 105% PPO NR
17 ± 4 SCI

26 ± 4 * AB 1.7 ± 0.3 161 ± 29

176 ± 17
160 ± 26

178 ± 12
Mean VO2peak from VER was higher than GXT in the AB group, although VO2peak was similar across protocols in SCI. There was no difference in HRpeak across all groups between protocols. Astorino et al. [13] CE NR RAMP

40 W for 2 min + 20 W/min
10 min active

recovery at 20 W
2 min WU at 20 W + cycling at 105% PPO A conservative difference in VO2max between protocols <0.06 L/min was used to identify ‘true’ VO2max
Astorino et al. [13] 2.0 ± 0.4 L/min NR 2.0 ± 0.3 L/min 1.5 ± 0.3 174 ± 13 174 ± 12 Bhammar et al. [32][24] CE RER ≥ 1.00,

HR ≥ 90% of

age-predicted HRmax

6 min at 40 W + initial WR of 20 W followed by 10–15 W/min
15 min of passive recovery 2 min WU at 20 W + cycling at 105% PPO Measured VER VO2max was considered higher than measured GXT VO2max when difference between measured VER and GXT VO2max was greater than the difference between predicted values
There was no difference in VO2 Bhammar et al. [29][25] [CE 29][HR > 85%

age-predicted HRmax;

RER > 1.15

40 W + 20 W/min for women

50 W + 25 W/min for men
15 min passive recovery 2 min WU at 30 W for women, 40 W for men + cycling at 105% PPO 25]VER-derived VO2max was higher than incremental VO2max when the difference between measured

VER VO2max and incremental

VO2max was greater
31 ± 6 NR 32 ± 6

than the difference between predicted VER and

incremental VO2max
2.1 ± 0.3 180 ± 11 180 ± 7 There was no difference in VO2max or HRmax between protocols, yet 3 of 11 participants exhibited a higher VO2max during VER compared to GXT. Bowen et al. [15] CE
Bowen et al. [15]BLa > 8 mM;

HR within 10% of age-predicted HRmax;

RPE > 18;

RER > 1.00–1.15

4 min at 10 W +

4–18 W/min
5 min active recovery at 10 W 4 min WU at 10 W + cycling at 95% PPO NR
14 ± 3 5.8–15.1 ± 0.5–1.9 15 ± 3 2.0 ± 0.4 117 ± 20 119 ± 26 Mean VO2peak and HRpeak were not different between protocols and VO2peak was confirmed in 60% of participants. Causer et al. [28][26] CE VO2
Causer et al. [28][26] plateau;

RPE > 9;

RER > 1.03–1.05;

Predicted VO2peak, PPO, or HRpeak

3 min at 20 W +

10–25 W/min
5 min cool-down at 20 W +10 min seated rest 3 min WU at 20 W +

cycling at 110% PPO
Less than 9% difference between protocols
35 ± 8 9.3 ± 2.3 33 ± 7 1.5 ± 0.4 168 ± 15 NR Dalleck et al. [10] CE RER > 1.0–1.15;

HR within 10 b/min of age-predicted HRmax;

VO2 plateau
STEP2 min WU at 50 W + 10–15 W/min 60 min passive

2 min WU at 50 W + cycling at 105% PPO Less than 3%

difference in VO2max between tests
Mean VO2peak did not differ between protocols, yet VER VO2peak was higher than GXT in 21% of participants.
Dalleck et al. [10] 28 ± 6 10.1 ± 2.1 27 ± 6 2.5 ± 0.5 165 ± 11 164 ± 10 Mean VO2max and HRmax were not different between protocols, although 11% of subjects exhibited higher VO2max and HRmax values with VER. de Groot et al. [25][23] TM
Frederike de Groot et al. [25][23]Heart rate = 95% (210–age);

RER > 1.0;

VO2 plateau

2% grade + 2 km/h + 0.25% change in grade/min or 3 km/h + 0.50% change in grade per min
4 min passive

34 ± 8110% peak speed Difference in VO2max between protocols >2.1 mL/kg/min
9.0 ± 4.0 35 ± 8 NR 184 ±20 NR Mean VO2peak was similar between protocols, yet 25% and 42% of participants showed a higher VO2peak and HRpeak in VER versus GXT. Leicht et al. [24][22] TM
Leicht et al. [24][22]VO2 plateau;

RER > 1.05

BLa > 4.0 mM;
23–40 ± 3–6

8.5–10.5 ± 0.5–2.5At least 2 days later 2 min rest + 5 min WU at 50 W +

cycling at 80–105% PPO
Misquita et al. [31][28] TM HRmax > 220–age; RER > 1.1;

VO2 plateau

Bruce protocol
1–2 min of slow walking +2 min at

0% incline at a speed eliciting 70%HRmax
Balke protocol TM grade was increased to 4% for 2 min and increased 2%/min NR
max or HRmax between protocols, although 5, 9, and 7 women revealed a verification VO2max > 0.06 L/min higher versus GXT.
Bhammar et al. [32][24] 40 ± 4 NO

27 ± 4 OB
9.7 ± 2.4 43 ± 4 * NO

28 ± 3 OB
2.2 ± 0.5 189 ± 6 NO

190 ± 13 OB
184 ± 8 NO

188 ± 12 OB
All children exhibited higher mean VER VO2max versus GXT, although there was no difference in HRmax. HR > 85%

age-predicted HRmax

Constant speed at 1% grade and grade

increased by 0.1–0.3%/min
5 min active recovery at 1 m/s at 1% grade Same peak speed as GXT but


gradient (+0.6% for PARA and NON-SCI; +0.3% for TETRA)
NR NR 125–188 ± 7–10 125–181 ± 7–15 VO2peak and HRpeak did not differ between VER and GXT in all subgroups. Athletes tended to exhibit a lower VO2peak in response to VER versus GXT. Mahoney et al. [26][27] CE
Mahoney et al. [26][27] 3.4 ± 0.4 L/minNR 8.3 ± 0.4 3.4–3.6 ± 0.5 L·min−1 2.5–6.9 ± 0.4–2.5 175 ± 12 170–177 ± 13–17 VER performed at 90% PPO elicits greater VO2max versus GXT, yet there was no difference in HRmax.
Misquita et al. [31][28] 19 ± 3 8.8 ± 1.9 20 ± 3 * 8.5 ± 1.9 156 ± 15 158 ± 14 VER revealed higher VO2peak versus GXT, although HRpeak was similar. Moreno-Cabañas et al. [14] CE
Moreno-Cabañas et al. [14]VO2 plateau;

RER > 1.1;

23 ± 8BLa 8 mM;

HR < 5% from

age-predicted HRmax

3-min WU at 30 W for women, 50 W for men + 15–20 W/min
5 min active recovery at 30 W + 15 min seated recovery 2 min WU at 30 W for women, 50 W for men + cycling at 110% PPO NR
7.9 ± 2.0 25 ± 8 * 2.1 ± 0.4 155 ± 15 156 ± 15 VER-derived VO2peak was higher than GXT, although there was no difference in HRpeak. Forty percent of participants show underestimated VO2peak in response to GXT that is confirmed with VER. Sawyer et al. [12] CE NR RAMP

5 min WU 50 W + 30 W/min for men

25 W + 15 W/min for women
Active recovery for 5–10 min at 25 or 50 W 100% PPO NR
Sawyer et al. [12] 2 ± 1 L·min−1 7.1 ± 1.9 2 ± 1 L·min−1 1.9 ± 0.4 174 ± 16 177 ± 13 * Mean VO2 Saynor et al. [33][29] CE NR RAMP

3 min at 20 W + 10–25 W/min
5 min active recovery at 20 W + 10 min passive seated recovery 3 min at 20 W + cycling at 110% PPO NR
Schaun et al. [22][21] TM ΔVO2 ≤ 150 mL/min; RER > 1.10; RPE ≥ 18; ± 10 b/min of 220–age STEP

3 min at 3 km/h + 0.5 km/h and 1% increments in speed and grade
10 min of passive recovery 2 min at 50% of peak speed/grade + 1 min at 70% peak speed/grade + exercise at 1 stage higher than GXT Difference in VO2max between protocols < 3%
Schneider et al. [21][30] CE RER ≥ 1.1;

HRmax ≥ 200 b/min–age

BLamax ≥ 8 mM;

RPE ≥ 18
Bhammar et al. RAMP

5 min WU at 20 W before power continuously increased that was individualized for each participant max was not different between protocols, yet HRmax was higher in VER. Thirteen and 8 participants achieved a VO2max and HRmax in response to VER that was ≥2% and 4–14 b/min higher than GXT.
Saynor et al. [33][29] 34 ± 3 8–12 NR NR 187 ± 15 NR VO2max values are reproducible in this sample in response to GXT and VER. STEP

20 W + 10 W/min
Schaun et al. [22][21] 22 ± 5 12 ± 2 24 ± 6 * 4.7 ± 0.4 150 ± 16 152 ± 16 VO2max was higher in response to VER versus GXT, although there was no difference in HRmax.
Schneider et al. 10 min passive recovery [21]cycling at 110% PPO [30]VO 21 ± 42max in VER does not exceed GXT-derived value by >3%
13.0 ± 2.9 21 ± 5 * 2.2 ± 0.3 150 ± 20 151 ± 21 VO2max from VER was lower than GXT, although there was no difference in HRmax. Sixty-eight percent of participants showed a ‘true’ VO2max with VER, although 32% elicited a 3–21% higher VO2max. Werkman et al. [30][31] CE
Werkman et al. [30][31]VO2 plateau;

HR > 95%

age-predicted HRmax; RER > 1.0

Unloaded cycling + 10 W/min < 120 cm; 15 W/min 120–150 cm; 20 W/min > 150 cm
39 ± 7 11.0 ± 3.0 39 ± 91 min passive recovery + 1 min unloaded cycling Test started with an increase in PO every 10 s based on each participant’s height NR
Wood et al. [11] TM VO2 plateau;

HR ± 11 b/min of age-predicted HRmax

RER ≥ 1.15;

BLa ≥ 8 mM;

RPE ≥ 18

4 min at 5.6 km/h −1 and 0% grade + increased velocity to a speed consistent with face-paced walk slow jog + 2.5% change in grade/min
5–10 min passive recovery 0.5 km/h above maximum workload in GXT achieved through increases in speed and/or grade Change in VO2 < 50% of that expected for the change in mechanical work
As far as the intensity of VER, 2 studies used a submaximal protocol [16[16][27],26], 15 studies used supramaximal work rates ranging from 105–115% PPO or above maximal TM velocity, and 3 studies [12,26,27][12][27][32] used workloads equivalent to PPO. Eight studies included specific criteria to identify differences in VO2max between protocols which were developed through reliability testing or predicted changes in VO2 for the change in work rate.

3. Differences in VO2max between Ramp and Verification Testing

Table 2 denotes VO2max values measured in response to GXT and VER for the studies included in this review. Results from 13 of 19 studies [5,9,10,11,12,13,23,24,25,28,29,30,33]
4.0 ± 1.0
177 ± 12
179 ± 13
There was no difference in VO
peak or HRpeak between protocols.
Wood et al.
34 ± 7
34 ± 7 NR 180 ± 10 180 ± 10 Neither VO2peak nor HRpeak were different between protocols.

4. Differences in HRmax between Ramp and Verification Testing

HRmax values from GXT and VER are demonstrated in Table 3. Similar to VO2max, the majority of studies exhibit no differences in maximal HR between protocols. Results from one study in obese adults [12] revealed a higher HRmax in response to VER, although another study [9] showed lower HRmax with VER versus GXT.

5. Exercise Duration of Verification Testing

Table 2 shows durations of VER reported in the studies. The shortest duration was equal to 1.5 min [13], with this VER protocol lasting up to 7 min in obese adults performing this bout at 80% PPO [26][27]. Twelve of nineteen studies were characterized with VER duration less than 3 min [9,12,13,14[9][12][13][14][15][30][20][27][32][26][25][24],15,21,23,26,27,28,29,32], with five studies having duration equal to or less than 2 min [12,13,15,23,28][12][13][15][20][26].

6. Discussion

Despite the widespread testing and application of VO2max in the fitness, clinical, and research setting, there is no universal approach to confirm its attainment from graded exercise testing. Verification testing is another widely adopted method to perform this function, yet it has been criticized for requiring an additional intense effort that may be inappropriate in those who are not active or healthy. A prior review by Poole and Jones [34][33] emphasized the widespread implementation of verification testing to identify a ‘true’ VO2max rather than ‘VO2peak’ in healthy active adults. In contrast, recent work [19] in active young and older men concluded that verification testing is unnecessary due to lack of differences in mean VO2max between the incremental and verification-derived value. The current review adds to this dogma by summarizing existing results from a large population of unhealthy adults and children completing verification testing following a GXT. Obtaining the most accurate VO2max value in this population is vital as it may lead to misrepresentations in their health status or responsiveness to training, which may in turn lead to inappropriate courses of treatment. Results reveal that most studies show no differences in aggregate VO2max between protocols. However, six studies show that VER elicits significantly higher estimates of VO2max, which supports its use when utmost accuracy is required in determining a ‘true’ VO2max on that day of testing.
Identifying differences in VO2max between GXT and VER requires that scientists are aware of the magnitude of error in VO2max estimation for both protocols. The error inherent in repeated VO2max testing ranges from 2–9% [7,14,28[7][14][26][34],35], with the error in acquiring gas exchange data from a metabolic cart being small (40 mL/min for the Parvo Medics system). This suggests that the remainder of the error is biological and likely related to participants’ ability and motivation to tolerate near maximal exercise. We recommend that scientists perform repeated testing to develop typical error values for their lab and use these values when comparing individual VO2max values between protocols rather than only comparing aggregate values. This approach, albeit time intensive, is preferred since relying on other laboratories’ criterion values is inappropriate due to differences in exercise protocol, equipment, patient population, pre-test dietary and physical activity restrictions, and time averaging intervals, which likely induce small changes in oxygen uptake.
A primary criticism of supramaximal VER testing is that this effort is too intense for inactive, unhealthy, or deconditioned adults to tolerate, resulting in a very brief duration of exercise and greater potential to not attain VO2max due to slow O2 kinetics. However, data from multiple studies [12,15,28,29][12][15][26][25] using supramaximal VER with exercise duration <2 min exhibit no differences in VO2max between protocols, similar to studies [9,10,29,30][9][10][25][31] in which VER duration lasted between 2–4 min. A recent study in hypertensive adults [22][21] used a multi-stage verification protocol eventually requiring a supramaximal workload. Results showed a significant underestimation of mean and individual VO2max values in response to GXT compared to VER. In nine obese adults with VO2max equal to 35 mL/kg/min [26][27], VER at 105% PPO elicited significantly lower exercise duration (167 s) compared to VER at 80% PPO (418 s), although there was no difference in VO2max between tests. However, VER performed at 80 (+0.16 L/min, 5% higher) and 90% PPO led to a higher VO2max value (+0.24 L/min, 7% higher) versus GXT, although this latter result was a trend (p = 0.06). Bhammar et al. [29][25] reported that a minimum exercise duration to attain a plateau in VO2 in response to VER in patients with hypertension was 80 s. These results seem to indicate that the appropriate or minimum duration required to allow attainment of ‘true’ VO2max using VER in unhealthy adults and children is similar to that recommended for healthy and active individuals. Thus, it is possible that submaximal intensities or multi-stage protocols may optimize VO2max values compared to GXT, although additional work in larger samples is needed to confirm this result.
Our review corroborates results from healthy, fit adults [17,36][17][35] showing no difference in HRmax between GXT and VER. However, a subset of data presented in this study [36][35] from participants with average cardiorespiratory fitness, exhibited significantly lower HRmax (−3 b/min) in response to VER compared to GXT. This is likely a result of the stepwise protocol used in this study that is characterized by a work rate less than PPO eliciting VO2max combined with a relatively long exercise duration (~20 min) versus the traditional 8–12 min ramp protocol. In contrast, obese adults performing VER at 100% PPO expressed significantly higher HRmax (+3 b/min) versus GXT [12], which may be attributed to their unfamiliarity with vigorous exercise during the initial incremental bout. To identify a ‘true’ VO2max, Midgley and Carroll [37][36] denoted a difference in HRmax < 4 b/min between GXT and VER. This value encompasses the magnitude of differences in HRmax described in the above studies, so it is likely that these discrepancies in HRmax between protocols are not clinically meaningful.
Considerations as to the exact characteristics of the recovery interval between GXT and VER include the intensity of the verification test, duration of GXT, cardiorespiratory fitness of participants, as well as a potential need to reduce the overall time of the session. Our review (Table 1) shows durations as brief as 2–5 min between protocols [24[22][23][32][31][28],25,27,30,31], 5–15 min [13,14,15[13][14][15][21][22][26][24][29],22,24,28,32,33], to as long as several days between protocols [10,27][10][32]. A recent systematic review [17] concluded that there was no effect of recovery interval on the difference in VO2max between protocols, which would suggest that any duration is appropriate. It is also apparent that some studies require an active recovery between protocols [13[13][15][20][28],15,23,31], whereas a passive recovery is completed in other investigations [11,14,22,25,29,32][11][14][21][23][25][24]. We recommend that scientists perform preliminary testing to identify an optimal recovery protocol for their specific population, and if this is implausible, then we recommend that they duplicate previously used procedures for that population.
Verification testing is only appropriate to identify ‘true’ VO2max if it is safe and well-tolerated by the participant completing exercise testing. This factor is especially critical in persons unfamiliar with vigorous exercise who may face enhanced risk of complications during vigorous exercise. In male and female survivors of cancer, Schneider et al. [21][30] reported no adverse events in their participants performing VER at 110% PPO. Furthermore, use of VER in adults with heart failure [15], hypertension [29][25], and metabolic syndrome [14] was described as “feasible” and “well-tolerated” in these populations at risk for or having heart disease. In children with cystic fibrosis [33][29], it was labeled as “safe.” Although further work is needed to substantiate this, empirical results suggest that VER following GXT is a safe and well-tolerated procedure that does not induce contraindications to exercise testing in persons who are inactive, have known disease, or exhibit enhanced risk of cardiometabolic disease. This guideline encompasses all VER protocols requiring efforts at submaximal, maximal, or supramaximal work rates. The only disadvantage to VER seems to be the extra time commitment required of approximately 15–20 min, including the recovery between protocols. However, this extra time is acceptable if the primary goal of testing is to acquire the most precise estimate of VO2max, which is critical in “at-risk” individuals when VO2max testing is used to identify health status or determine the effects of exercise training.
There are a few limitations to this review. First, the marked diversity in patient populations used and the specific GXT and VER protocol completed preclude us from making universal recommendations regarding an optimal verification test. Nevertheless, it seems that submaximal or supramaximal work rates can be employed with little difference in resultant VO2max values expected versus GXT. Second, with exception of a few studies [11[11][14][30][28],14,21,31], the sample size of individual studies is relatively small, which reduces the generalizability of these findings. Consequently, we recommend that scientists follow experimental procedures used in single studies that utilized their target population. Third, the use of VER following GXT likely elicits the highest estimate of VO2max on that day, yet it is possible that additional testing on subsequent days could elicit higher estimates of VO2max, as recently shown [38][37]. However, requiring multiple sessions of exercise including GXT and VER on many days may not be appropriate in unhealthy participants due to time and health related challenges.


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