As perioperative medicine develops as a specialty, defining “fitness for surgery” will remain a priority, requiring recognition of suitable objective measures to determine levels of perioperative risk (Pearse et al.
2006; Pearse et al.
2011). The outdated perception that advanced chronological age has a “cause and effect” relationship with the increased surgical risk (Findlay
2011) has already been replaced by concentration on more specific measures of patient risk, including pre-operative frailty (Partridge et al.
2012; Makary et al.
2010), cognitive dysfunction (Bettelli
2011) and sarcopaenia (Englesbe et al.
2013).
Once developed, robust risk-stratification metrics will initially be used to inform pre-operative decision-making and the rational use of scarce post-operative resource. In addition, their role in the development of pre-operative interventions aimed at improving surgical recovery will be significant. However, such an interventional approach to pre-operative functional improvement has been limited, primarily by a lack of timely patient assessment in the context of challenging cancer and elective surgical targets.
If the perioperative medicine vision, recently presented by the Royal College of Anesthetists, is to become reality, a close synergy between well-organised patient assessment and the detection of robust objective risk markers, will lead the way towards the development of appropriately managed pre-operative interventions, applied early enough in the surgical pathway to make a difference.
The perioperative field has recently adopted the term “pre-habilitation” (Jack et al.
2011; Carli et al.
2012; Gillis et al.
2014). Loosely defined, it may refer to a group of interventions, integrated into the clinical pathway before a surgical procedure and aimed at both reducing imminent patient risk and promoting lasting beneficial effects on perioperative recovery and outcome. Presently, most of these interventions are based around simple lifestyle change including alcohol or smoking cessation, dietary measures or increasing physical activity above sedentary levels. Our focus here is on structured physical activity in the form of pre-surgical exercise interventions, the effectiveness of which has been the subject of several recent systematic reviews. Valkenet and colleagues (Valkenet et al.
2011) reported pre-operative exercise therapy to be effective for improving post-operative length of hospital stay and complication rate in patients undergoing cardiac or abdominal surgery and should therefore be considered as standard pre-operative care. More recently, a systematic review of 10 studies (1 to 12 weeks in duration) examining pre-operative aerobic exercise training in patients awaiting intra-cavity surgery reported training to be generally effective in improving physical fitness (O’Doherty et al.
2013). This finding concurs with that of Pouwels et al. (
2015) who systematically reviewed five studies and reported that current evidence shows pre-operative exercise therapy in abdominal aortic aneurysm patients has potential beneficial effects. The beneficial effects of pre-operative exercise extend beyond patients undergoing abdominal or cardiac surgery as Singh et al. (
2013), following a systematic review of 18 pre-surgical exercise intervention studies (median of 21 days in duration) with cancer patients, reported that pre-surgical exercise protocols containing cardiovascular and resistance exercise resulted in functional and clinical benefits that are critically important in cancer care. Therefore, despite cancer patients often receiving a diverse range of systemic cytotoxic therapies, due to a range of comorbities, that can be associated with the potential to increase the risk of exercise-related complications (Jones et al.
2010), exercise training is safe during and after cancer treatments and results in improvements in physical functioning and quality of life (Schmitz et al.
2010).
Given the increased evidence in support of pre-surgical exercise interventions, pre-operative exercise therapy is therefore likely to develop as a major component of pre-habilitation. This is not simply because exercise is known to improve cardiorespiratory function, but because of the well-documented benefits of exercise on multiple organ systems. Accepting existing cardiorespiratory function, however it is measured, as a binary concept of “fitness for surgery” is shortsighted and enforces passivity. Cardiorespiratory function in the context of an elective surgical procedure is not an end point—it is a potential starting point to therapy that may have a lasting benefit well beyond the perioperative period. The time between “decision to treat” and operation becomes an important “treatable moment”, with the opportunity to assess what part physical activity or exercise plays in the individual’s lifestyle, whether there is a general requirement to change and what support and guidance is required to motivate them to play an active role in their own pre-operative preparation. Furthermore, regaining fitness, maintaining fitness, improving fitness or indeed losing fitness could all be potential outcomes of the way clinical staff accept and promote the concept of pre-operative improvement in activity status related to their patients. Nevertheless, even where all the elements for successful behavioural modification are optimised to adapt and integrate exercise programmes into the pre-operative process, there will always be the need for appropriately designed, timely and individualized exercise programmes.
A recent article (Durrand et al.
2014) highlighted the possibility that lessons learned from exercise training within sports medicine and sports science may be transferrable to clinical practice to benefit patient outcomes. While such a notion is clearly in its infancy, we agree that the cross-fertilization of sports science with clinical practice can only help to better inform future pre-habilitative exercise interventions. Therefore, in this commentary, it is our intention to disseminate contemporary exercise intervention research from both clinical and non-clinical populations, with the ultimate aim of beginning to inform the design and prescription of effective and time-efficient exercise strategies for use prior to surgery.
Physical activity, exercise and cardiorespiratory function
Physical activity is defined as any bodily movement produced by skeletal muscle that results in energy expenditure (Caspersen et al.
1985). Leisure time physical activity, as the name suggests, encompasses activities completed during an individual’s free time, whereas occupational physical activity is performed as part of employment (Findlay
2011; Howley
2001). Exercise is a subset of leisure time physical activity that is planned, structured and repetitive. Often, exercise is undertaken to improve and/or maintain components of physical fitness (Pearse et al.
2006; Pearse et al.
2011; Howley
2001). A subjective definition of physical fitness relates to an individual’s ability to perform everyday tasks with alertness and vigour, free of unnecessary fatigue, and with ample energy to enjoy leisure activities (Partridge et al.
2012; Makary et al.
2010; Caspersen et al.
1985). More objectively, physical fitness is a set of measureable health and performance-related attributes or characteristics that include cardiorespiratory function, muscular strength and endurance, body composition, flexibility, balance, agility, reaction time and power (Bettelli
2011; Caspersen et al.
1985; Howley
2001). Of these, cardiorespiratory function (the ability of the cardiovascular and respiratory system to supply oxygen to the working muscles during dynamic exercise) (Englesbe et al.
2013; Howley
2001) is of particular interest from a perioperative standpoint. Indeed, it has been shown that cardiorespiratory function is an independent predictor of mortality and length of hospital stay (Findlay
2011; Snowden et al.
2013) and that higher levels of pre-operative function are associated with significantly improved survival rates in individuals undergoing numerous major non-cardiac surgical procedures (Jack et al.
2011; Carli et al.
2012; Durrand et al.
2014; Snowden et al.
2013; Moyes et al.
2013; West et al.
2014; Snowden et al.
2010; Prentis et al.
2012; Older and Hall
2004). The physiological rationale relating improved cardiorespiratory function with reduced post-surgery adverse outcomes is strong—patients with adequate fitness levels will be able to better meet the neuroendocrine, metabolic and inflammatory demands of the surgery (Tew et al.
2014). Accordingly, the pre-operative period may represent a good time to engage patients in enhancing cardiorespiratory function (Durrand et al.
2014; Carli et al.
2010), with exercise training representing a plausible interventional strategy for improving surgical outcome (Gillis et al.
2014; Snowden and Minto
2015).
Developing exercise programmes for surgery
When prescribing any exercise training programme, consideration should be given to the frequency, intensity, time, type, volume and progression (FITT-VP) principles (American College of Sports Medicine
2013). Each of these principles will be discussed in the following sections, in the context of the current UK physical activity guidelines, and exercise interventions conducted across clinical and healthy populations. Our examples will be centred on high-intensity interval training (HIT), which typically involves repeated repetitions of intense exercise, interspersed with periods of rest or low intensity active recovery (Fox et al.
1973). This is in light of accumulating evidence supporting the use of HIT to elicit substantial improvements in the cardiorespiratory fitness of patient (Weston et al.
2014a; Liou et al.
2015) and non-patient populations (Sloth et al.
2013; Gist et al.
2014; Weston et al.
2014b).
Intensity
describes, in relative or absolute terms, the effort associated with the exercise. Of the FITT-VP principles, intensity is often the most important determinant of the physiological response to the exercise training (Hickson et al.
1985). As the individual response to exercise differs depending on initial fitness levels, it is recommended that exercise prescription is based on a relative measure of intensity (e.g. the energy cost of the exercise relative to the individual’s maximal capacity), rather than an absolute value (Garber et al.
2011). This is especially true for older and deconditioned populations (Howley
2001; Nelson et al.
2007).
The intensity of cardiorespiratory (endurance/aerobic) exercise can be explained practically to patients with the talk test whereby moderate exercise intensity enables a patient to comfortably hold a conversation, and high-intensity exercise precludes comfortable conversation; however, more accurate methods are available that use ratings of perceived exertion or heart-rate training zones (Jones et al.
2010). As such, relative exercise intensity can be assessed in various ways, ideally using either percentage of maximal oxygen uptake (VO
2max), determined via a cardiopulmonary exercise test (CPET), heart rate (either percentage of maximal heart rate [HR
max] or heart rate reserve) and individual’s perception of effort using Borg’s ratings of perceived exertion (RPE) scales (Borg
1982), with training intensities in perioperative training programmes predominately based on the latter of these measures (Jack et al.
2011). A combination of objectively and subjectively prescribed exercise intensity is likely to represent best practice here. A recent example of this was provided by Tew et al. (
2014) whereby the intensity of exercise for the first training session was performed at the power output associated with ventilatory threshold determined on baseline CPET. In subsequent sessions, power output was gradually manipulated until the patient reports a perceived exertion of 6 to 7 on Borg’s CR-10 scale (Borg
1982) at the end of each work interval.
Heart rate monitoring represents a simple and reliable measure of exercise intensity and is widely considered as one of the best and most popular ways to prescribe and monitor exercise intensity (Impellizzeri et al.
2004). Often, however, patient medication can reduce the reliability of the exercise heart rate data. In situations whereby heart rate is difficult to estimate (e.g. arrhythmia or medication such as beta blockers), RPE are generally considered reliable (Eston and Williams
1988; Buckley et al.
2009) and training studies have demonstrated similar beneficial health effects when patient exercise intensity is guided by RPE compared with other more objective physiological monitoring methods (Ilarraza et al.
2004; Zanettini et al.
2012). Further, recent findings on the association between changes in RPE and heart rate during graded aerobic exercise indicate that RPE can indeed help guide exercise intensity in everyday clinical practice (Tang et al.
2015). Assuming patient familiarisation and correct researcher instructions, we recommend the use of Borg’s scales (Borg
1982), as these scales are valid for prescribing exercise intensity in clinical settings (Impellizzeri et al.
2011).
The measures described above aid categorisation of intensity of exercise training programmes. In recent guidance from the ACSM on exercise prescription (Garber et al.
2011), the term “moderate intensity” is used to describe exercise performed at either 46 to <64 % of VO
2max, 64 to <76 % HR
max, or 12 to 13 on Borg’s 6 to 20 RPE scale. “Vigorous intensity” defines exercise completed at 64 to <91 % of VO
2max, 76 to <96 % of HR
max, or an RPE of 14 to 17; whereas exercise performed at ≥91 % of VO
2max, ≥96 % of HR
max, or at an RPE ≥18 is described as “near maximal” or “maximal”. It should, however, be noted that while these descriptors are helpful, they do not represent universally standardised terminology for intensity quantification within the exercise science literature. Indeed, the intensity of an exercise programme can often fall between the aforementioned ranges. An example of this is HIT, which is typically performed at ≥90 % HR
max, therefore necessitating short interval durations (often ~30 to 60 s) and longer recovery periods. Over the last decade, there has been a surge of scientific interest on the efficacy of HIT, such that there is now accumulating evidence that, when performed over several weeks, HIT is a more effective means of improving cardiorespiratory fitness than prolonged sessions of moderate-intensity exercise (Weston et al.
2014a; Liou et al.
2015; Milanović et al.
2015). Indeed, following a meta-analysis of HIT in patients with lifestyle-induced cardiometabolic disease, Weston et al. (
2014a) reported that HIT increased cardiorespiratory fitness by almost double (19.4 vs 10.3 %) that of moderate intensity continuous exercise (e.g. 50 to 60 % of VO
2max). As such, there is a consensus for the benefit of HIT for improving cardiorespiratory fitness in patient populations (Weston et al.
2014a; Liou et al.
2015; Kessler et al.
2012; Pattyn et al.
2014).
Type
refers to the mode of exercise being undertaken (e.g. walking, running, cycling, dancing and resistance training). In the past, attributes such as power, balance and reaction time were described as aspects of “performance-related fitness”, such that they were almost exclusively associated with sporting performance outcomes (Howley
2001). However, it is now widely acknowledged that many basic daily activities are dependent on the ability to generate force at high velocity (Weston et al.
2014b), and therefore, power/strength training is associated with improved mobility-related outcomes, self-efficacy, satisfaction with physical function and overall life satisfaction in the elderly (Katula et al.
2008; Hruda et al.
2003). This is recognised by the inclusion of specific strength (resistance) training guidelines for adults and older adults in the current UK physical activity guidelines. It should therefore come as no surprise that, alongside cardiorespiratory fitness, pre-operative functional status can help to identify patients at higher risk of post-operative complications (Saxton and Velanovich
2011). Perioperative exercise training programmes should thus aim to improve cardiorespiratory fitness and muscle strength (Snowden and Minto
2015).
The combination of endurance training and strength training within the same training programme is referred to as “concurrent” training. While the combination of endurance and strength training is an effective means of improving strength/neuromuscular and cardiorespiratory function in healthy older adults (Cadore and Izquierdo
2013; Cadore et al.
2014; Wilhelm et al.
2014; Berryman et al.
2014; Burich et al.
2015) and patient populations, (Iepsen et al.
2015; Casla et al.
2015; Buffart et al.
2015) there is some evidence to suggest that concurrent training attenuates gains in muscle mass, strength and power compared with undertaking resistance training alone (Fyfe et al.
2014). However, the majority of literature investigating concurrent training has implemented continuous or continuous and interval endurance training protocols alongside strength training (Cantrell et al.
2014), and interference effects of endurance training are a factor of the mode, frequency and duration of the endurance training selected (Wilson et al.
2012). As such, the possibility exists that it is the total volume of endurance exercise, rather than the intensity, that may be more crucial in mediating concurrent interference (Fyfe et al.
2014; de Souza et al.
2013) and therefore, low-volume HIT protocols might confer benefit over traditional endurance training by limiting any potential volume-dependent interference effect, while also offering a similar, if not better, fitness benefit (Liou et al.
2015; Milanović et al.
2015; Fyfe et al.
2014; Cantrell et al.
2014). Ultimately, performing two types of training within the same training programme (e.g. aerobic and strength) requires an increased time commitment. Low-volume HIT can negate this, however, as simultaneous improvements aerobic fitness and strength/power have been observed following this type of training programme (Cantrell et al.
2014; Rodas et al.
2000; Zelt et al.
2014; Buckley et al.
2015); therefore, introducing a low-volume HIT programme into the perioperative care pathway has further appeal here.
The prevalent type of exercise dominating the sport and clinical HIT literature is the lower body—either cycling or treadmill walking/running (Tew et al.
2014; Weston et al.
2014a; Sloth et al.
2013; Gist et al.
2014; Weston et al.
2014b; West et al.
2015). Yet, activities of daily living require a synergy of lower and upper body fitness, and recent evidence, albeit with a small group of young to middle-aged healthy males, shows of little transfer from lower body training to upper body gains (Osawa et al.
2014). Therefore, more consideration could be given to the type of exercise prescribed for perioperative interventions. For example, Osawa and colleagues (Osawa et al.
2014) reported that a HIT programme combining upper and lower body exercise led to improved upper and lower body aerobic capacity, while also promoting muscle hypertrophy of key stabilising musculature. Heinrich et al. (
2014) recently provided experimental findings that add further to the appeal of combined upper and lower body HIT. Here, the authors used “crossfit” (incorporating combined intensive upper and lower body exercises such as squats, push-ups, etc.), as the type of HIT and reported that, when compared to traditional aerobic and strength training exercises, participants spent significantly less time exercising per week, yet were able to maintain exercise enjoyment and were more likely to intend to continue (Heinrich et al.
2014). Therefore, a low-volume HIT programme delivered via exercises using a combination of upper and lower body exercises/movements would represent an attractive perioperative fitness training strategy by improving both cardiorespiratory fitness and strength/power in a time-efficient manner.
Other considerations
At the individual session level, consideration should be given to the training principles of intensity, time and type. When developing an exercise programme spanning a number of weeks or months (less likely in the pre-surgical context), however, thought must also be given to how often the sessions will take place, how they will progress over time and the overall volume of exercise prescribed. Consideration should also be given to the perceived barriers to exercise participation that patients may face. For example, opponents of HIT, and in particular low-volume HIT, often highlight that the intense physical effort required and associated fatigue may be detrimental to motivation (Sparling et al.
2015). This claim, however, has not been evidenced in the literature as adherence rates to clinical and non-clinical HIT programmes have been high, albeit in relatively small samples sizes, and often display better adherence than “traditional” moderate-intensity exercise programmes (Wisloff et al.
2007; Currie et al.
2015). Further discussion surrounding this topic can be found elsewhere (Biddle and Batterham
2015).
It has also been suggested that performing HIT may increase injury risk and medical complications (Lunt et al.
2014). While these are important issues to be aware of, risks can be greatly minimized through proper consideration of the FITT-VP principles from the programme onset, and ensuring that the exerciser performs an adequate warm-up. Ensuring that exercise intensity is set relative to the individual’s capacity, as opposed to a standardised value, can also prevent stagnation, over-exertion and the risks associated with this. Furthermore, following a recent systematic review of HIT in patients with cardiovascular and metabolic diseases, Levinger et al. (
2015) reported that in all studies, the rate of adverse responses was low, and HIT sessions were well tolerated overall across all patients. We concur with the safety advice provided by these authors whereby patients undertaking HIT should be clinically stable, have had recent exposure to at least regular moderate intensity exercise, undertake the training in facilities that have both the equipment and the expertise to handle adverse responses and have appropriate supervision and monitoring during and after the exercise session.
Perioperative exercise training represents a credible means for improving surgical outcome. In this commentary, we have attempted to combine contemporary exercise training research from both exercise science and clinical science, to inform on key issues related to exercise training programme design, namely frequency, intensity, time, exercise type, volume and training progression. Collectively, the evidence presented on the FITT-VP principles with regard to HIT support its use as a promising perioperative strategy for enhancing cardiorespiratory fitness. We are not suggesting that HIT should be used as a replacement for all other forms of exercise and physical activity; however, given the need for pre-surgery exercise interventions to be both effective and time efficient, we believe that carefully designed and supervised HIT programmes targeting the upper and lower body and tailored to the individual, represent a valuable addition to the perioperative pathway of care.
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Competing interests
The authors declare that they have no competing interests. No sources of funding were used to assist in the preparation of this commentary.
Authors’ contributions
MW, KW, JP and CS conceived the article and contributed to the writing of the manuscript. All authors read and approved the final manuscript.