The cardiovascular and respiratory systems support increased energy requirements of the musculature during physical activity. The functional limit of the cardiovascular system can be best assessed through the maximal oxygen uptake test ([??][O.sub.2]max), which is commonly defined as an index of cardiorespiratory fitness and typically reflects the upper limit of the body's ability to intake and consume oxygen (Astrand and Saltin, 1961). Nevertheless, the term "peak oxygen uptake" ([??][O.sub.2]peak) is used in the present paper, as it reflects more precisely a stress test in a clinical setting where the exercise test termination could be due to other than cardiorespiratory limitations. Recent research has explored how upper-limb aerobic exercise can be applied in clinical populations (Ilias et al., 2009). More specifically, this exercise modality seems to be appropriate for cardiorespiratory fitness assessments aimed at patients having limited functional capacity in the lower limbs. In clinical settings the cardiopulmonary exercise (V[O.sub.2]peak) test has been established as an approved pre-operative examination (Weisman et al., 2003). More specifically, [??][O.sub.2]peak and anaerobic threshold have been demonstrated as an index of patients' physiological tolerance for major surgery (Davies and Danjoux, 2010). Anaerobic threshold has also been associated with postoperative mortality (Older et al., 1999) and its concomitant use for pre-operative risk stratification (Orr et al., 2013). Moreover, arm exercise has been demonstrated to predict clinical outcomes (Chan et al., 2011; Ilias et al., 2009) and researchers reported that the prognostic value of the clinical data obtained during arm exercise may be equivalent to that reported for treadmill or cycle ergometer exercise (Dutcher et al., 2007; Myers et al., 2002).
Arm crank ergometry (ACE) seems to constitute a reliable mode of exercise that is able to assess all the physiological responses that are elicited during physical activity. Several factors are considered to play a vital role in eliciting significant physiological responses during arm crank ergometry including crank rate (Schrieks et al., 2011; Smith et al., 2001), the type of incremental protocol (Sawka et al., 1983; Smith et al., 2004), and the ramp slope during an incremental ramp protocol (Castro et al., 2010). These studies have demonstrated that a crank rate of 70 revolutions per minute is considered to be the optimal 'tempo' during a [??][O.sub.2]peak test and that a continuous incremental ramp protocol induces higher values of oxygen uptake, ventilation and heart rate responses compared with slower crank rates. Furthermore, fast (increment: 2W/6 s) and slow (increment: 1W/6 s) ramp protocols seem equal in attaining peak oxygen uptake in healthy young individuals (Castro et al., 2010).
Cycle ergometry is routinely used in clinical settings in many European countries. In addition, cycle ergometry compared with treadmill testing is cost-effective, requires less space and is a feasible alternative in individuals who are obese or those presenting with orthopaedic, peripheral vascular, and/or neurological limitations. Therefore, it is a widely-used exercise modality in clinical populations. Nevertheless, a validated arm crank ergometer protocol whose values are strongly associated with cycle ergometer measures for the prediction of [??][O.sub.2]peak has yet to be established.
Wasserman's cycle ergometer test ramp protocol (Wasserman, 1976) is a validated and widely used test in the clinical setting when patients are assessed for either cardiovascular or cardiorespiratory limitations. This protocol is practical and preferable for patients as they do not experience sudden increases in work rate, which is the case with graded test protocols (Wasserman et al., 2012, p. 141-2). Nonetheless, some patients may not be able to pedal either due to lack of coordination and cycling experience and / or may experience seating discomfort during a long test. However, anecdotal reports from patients' highlight the most common reason for not being able to pedal is restricted lower limb mobility.
In cases where a cardiopulmonary test is essential for screening prior to surgery a predictive [??][O.sub.2]peak value from an arm crank ergometer would be useful. The estimation of [??][O.sub.2]peak from an arm crank test would be of use for clinicians not only for pre-operative risk stratification but also for routine cardiopulmonary exercise test (CPET) in adults with restricted lower limb mobility. For example during a CPET the clinician assesses the electrical signs of the heart through an electrocardiogram (ECG) and the cardiovascular responses such as [??][O.sub.2]peak that would be induced by an arm crank test. However, there is lack of evidence for cut-off values in ACE [??][O.sub.2]peak that would be of use for disease and/or mortality prognosis. Therefore, the application and usefulness of a predictive [??][O.sub.2]peak equation resulting from an arm-crank test setting seems warranted.
The purpose of the present study is to produce an equation that will be able to predict cycle ergometer [??][O.sub.2]peak, using ACE physiological outcomes as equation elements. The study would also determine the differences in physiological responses in ACE and a cycle ergometer test protocol in middle-aged adults with low-to-moderate cardiovascular risk, following the most recent ACE test protocol recommendations (e.g., Castro et al., 2010; Wasserman et al., 2012).
Twelve middle-aged adults (6 men and 6 women, mean age 55.1 [+ or -] 5) were recruited from the Sheffield Hallam University voluntary database. All participants lived a sedentary lifestyle, had office-based employment, with no training history as athletes of any sport. Participants underwent health screening to confirm the absence of any cardiovascular and/or metabolic disease. Each participant received a study information sheet and became aware of any possible risks before signing the consent form. The research was approved by the Human Ethics Committee of Sheffield Hallam University and complied with the principles laid down in the Declaration of Helsinki.
A post-hoc analysis was performed according to the multiple regression analysis with input parameters of error (error probability = 0.05), the total sample size (n = 12) and the number of predictors (e.g., ACE[??][O.sub.2]peak, lean body mass lower limbs, total lean body mass). The result showed a statistical power of 0.99 which indicates that the total sample size was sufficient to predict any relationships between these two exercise modes.
Apart from a sedentary status, our inclusion criteria for participation consisted of ages [greater than or equal to] 45 for men and [greater than or equal to] 55 years for women, which are considered to be the cut-off age limits for each sex respectively, beyond which cardiovascular risk is increased according to American College of Sport Medicine (ACSM) guidelines (Pescatello et al., 2014). Participants were allowed [greater than or equal to] 2 risk factors without symptomatic, or known cardiovascular, pulmonary, renal, or metabolic disease. Prior to each...