Simulación del sistema completo

Prolonged continuous aerobic exercise generally has glucose lowering effects and therefore carries a risk of hypoglycaemia in patients with type 1 diabetes (Macdonald 1987, Tuominen et al. 1995, Riddell et al. 1999, Rabasa-Lhoret et al. 2001, Francescato et al. 2004, Tansey et al. 2006, West et al. 2010). However, not all forms of exercise acutely lower blood glucose, meaning some types of exercise may confer a lower risk of hypoglycaemia (Fahey et al. 2012). High-intensity exercise (such as sprinting) often results in an acute increase in blood glucose concentrations in patients with type 1 diabetes (Marliss and Vranic 2002, Fahey et al. 2012). This form of exercise induces a substantial increase in catecholamine release (≥ +Δ500% from rest (Fahey et al. 2012, Davey et al. 2013, Davey et al. 2014)) which can increase hepatic glucose output (Kjaer et al. 1986) at a greater rate than glucose clearance (Sigal et al. 1996). Exercise in intermittent form, short bursts of high intensity exercise interspersed with moderate intensity aerobic exercise, has been demonstrated to reduce the risk of hypoglycaemia early after exercise (Guelfi et al. 2005, Bussau et al. 2006, Bussau et al. 2007, Guelfi et al. 2007, Maran et al. 2010).

From a practical perspective the vast majority of studies suffer from short observation periods, which means it is difficult to assess the effectiveness of manipulating exercise for the prevention of late-onset hypoglycaemia (Guelfi et al. 2005, Bussau et al. 2006, Bussau et al. 2007, Guelfi et al. 2007, Maran et al. 2010, Campbell et al. 2014). Indeed, much of the work in this area was designed to simulate the demands of team games such as soccer, rugby and hockey (Guelfi et al. 2005, Guelfi et al. 2007, Maran et al. 2010, Campbell et al. 2014), rather than strategies to prevent hypoglycaemia per se. Much of this existing literature has focused

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predominantly upon cycling (Guelfi et al. 2005, Bussau et al. 2006, Bussau et al. 2007, Guelfi et al. 2007, Iscoe and Riddell 2011, Fahey et al. 2012, Davey et al. 2013, Davey et al. 2013), however cycling fails to adequately replicate the physiological demands of games-type activities, in which repeated changes in speed and direction are a major component. Cycling involves primarily concentric muscle actions (Bijker et al. 2002) meaning that the muscle shortens as it contracts, whereas in the majority of intermittent game-type activities, which typically involve running, a significant proportion of eccentric muscle action occurs, where the muscle lengthens during the contraction phase. This is a particularly important consideration in type 1 diabetes, as eccentric muscle actions have the potential to down-regulate the insulin receptor, thus hindering insulin action and glucose uptake following exercise (Asp et al. 1995). Moreover, weight bearing exercise, which typically requires greater muscle mass involvement (running versus cycling), has a greater energy demand (Robertson et al. 2009). Thus, the ecological validity of these studies is somewhat questionable, and the impact of exercise modality on late-onset hypoglycaemia has been under researched.

A recent investigation which I conducted outside of this series of studies (2014) aimed to address the limitations of these former studies, by comparing the 24 hour glycaemic responses to continuous versus intermittent running exercise, which was designed to closely simulate games-play. The results from this study indicate that the preservation in blood glucose early after exercise is only marginally greater following intermittent running, compared to continuous running exercise at a similar intensity (matched %V̇O2peak). Moreover, there was an

equal incidence of late-onset hypoglycaemia in this dataset, indicating that falls in glycaemia are likely to occur irrelevant of exercise modality.

Recently, resistance exercise in type 1 diabetes has received notable attention within the literature because this form of exercise also elicits similar hormonal and metabolic responses to that of intermittent and high-intensity running or cycling (Kraemer and Ratamess 2005). Resistance exercise results in a lesser decline in blood glucose immediately after exercise (Yardley et al. 2010), however, the risk of late-onset hypoglycaemia remains (Yardley et al.

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2013), irrelevant of exercise intensity (Silveira et al. 2014) or duration (Turner et al. 2013, Turner et al. 2014), whether this is incorporated into aerobic exercise or not (Yardley et al. 2010), and regardless of the order exercise is performed (Yardley et al. 2012).

Manipulating an acute hormonal response through altering exercise type, is likely to carry only short lasting effects on glycaemia (Yardley et al. 2013). Thus, it would appear that manipulating exercise modality alone is not a completely protective strategy against exercise- induced hypoglycaemia. Moreover, the majority of studies utilising high-intensity work in intermittent (Guelfi et al. 2005, Guelfi et al. 2005, Bussau et al. 2006, Bussau et al. 2007, Guelfi et al. 2007, Maran et al. 2010, Iscoe and Riddell 2011, Fahey et al. 2012, Davey et al. 2013) or resistance form (Yardley et al. 2010, Yardley et al. 2012, Turner et al. 2013, Yardley et al. 2013, Silveira et al. 2014), have typically recruited patients young in age (mean ~26 years, range 18-30 years), in good glycaemic control (HbA1c ~7.4%), and are already regularly

engaged in exercise; three studies include competitive athletes in their cohort (Iscoe and Riddell 2011, Yardley et al. 2012, Yardley et al. 2013). Results in these studies, may not necessarily be generalised to the wider population of type 1 diabetes patients, and may be inappropriate or even unachievable for many individuals considering not all studies demonstrate good adherence rates for novices (~62% adherence rate to exercise in type 1 diabetes (Plotnikoff et al. 2006)). Eccentric-based intermittent shuttle running exercise can induce severe muscle soreness and muscular dysfunction (Bailey et al. 2007), and has been observed as a primary mechanism of injury (Hawkins et al. 2001, Woods et al. 2004); the frequency of speed changes places greater emphasis on the acceleration and deceleration phases of the running cycle applying more eccentric load than conventional cycling based sprinting protocols (Greig and Siegler 2009). An increased risk of muscle soreness, fatigue, and injury are likely to deter older patients or those unaccustomed to such movement patterns. Additionally, research suggests that the performance of prolonged lower-intensity exercise confers similar gains in cardiovascular fitness (Wenger and Bell 1986) and carries greater long-term adherence rates (Perri et al. 2002) compared to shorter-duration, higher intensity

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training. In addition, aerobic exercises which are weight-baring, such as running and jogging, are likely to offer similar improvements in bone mineral density (Welsh and Rutherford 1996, Kelley et al. 2001) and deliver greater improvements in stability and maintenance of gait in older individuals (Sauvage Jr et al. 1992).