Matthew W. Bridge

Carbohydrate sensing in the human mouth : effects on exercise performance and brain activity

Exercise studies have suggested that the presence of carbohydrate in the human mouth activates regions of the brain that can enhance exercise performance but direct evidence of such a mechanism is limited. The first aim of the present study was to observe how rinsing the mouth with solutions containing glucose and maltodextrin, disguised with artificial sweetener, would affect exercise performance. The second aim was to use functional magnetic resonance imaging (fMRI) to identify the brain regions activated by these substances. In Study 1A, eight endurance‐trained cyclists ( 60.8 ± 4.1 ml kg−1 min−1) completed a cycle time trial (total work = 914 ± 29 kJ) significantly faster when rinsing their mouths with a 6.4% glucose solution compared with a placebo containing saccharin (60.4 ± 3.7 and 61.6 ± 3.8 min, respectively, P= 0.007). The corresponding fMRI study (Study 1B) revealed that oral exposure to glucose activated reward‐related brain regions, including the anterior cingulate cortex and striatum, which were unresponsive to saccharin. In Study 2A, eight endurance‐trained cyclists ( 57.8 ± 3.2 ml kg−1 min−1) tested the effect of rinsing with a 6.4% maltodextrin solution on exercise performance, showing it to significantly reduce the time to complete the cycle time trial (total work = 837 ± 68 kJ) compared to an artificially sweetened placebo (62.6 ± 4.7 and 64.6 ± 4.9 min, respectively, P= 0.012). The second neuroimaging study (Study 2B) compared the cortical response to oral maltodextrin and glucose, revealing a similar pattern of brain activation in response to the two carbohydrate solutions, including areas of the insula/frontal operculum, orbitofrontal cortex and striatum. The results suggest that the improvement in exercise performance that is observed when carbohydrate is present in the mouth may be due to the activation of brain regions believed to be involved in reward and motor control. The findings also suggest that there may be a class of so far unidentified oral receptors that respond to carbohydrate independently of those for sweetness.

The specialising or sampling debate: a retrospective analysis of adolescent sports participation in the UK

Abstract Whether young people should specialise in one competitive sport at an early age, or pursue a wider range of sports during adolescence is a topic of some debate (Baker, Cobley, & Fraser-Thomas, 2009) and is fundamental within sports policy and coaching practice. The purpose of this retrospective recall study was to identify whether early specialisation or sporting diversification (sampling) throughout childhood and adolescence can influence performance levels prior to adulthood. An online questionnaire was used to collect the sport participation histories of 1006 UK sports people, which were then compared with the developmental framework provided by the Developmental Model of Sport Participation (DMSP, Côté & Fraser-Thomas, 2007). A significant association between the number of sports participated in at the ages of 11, 13, and 15 and the standard of competition between 16 and 18 years was found. Individuals who competed in three sports aged 11, 13, and 15 were significantly more likely to compete at a national compared with club standard between the ages of 16 and 18 than those who practised only one sport. The findings reported here provide some empirical support for the sampling performance pathway DMSP model in a UK context.

Associations between children's physical activities, sedentary behaviours and family structure: a sequential mixed methods approach

This mixed method paper explored the effect of family structure on childrens physical activities and sedentary pursuits. It furthers the limited understanding of how family structure impacts on childrens time in, and reasons behind engaging in, certain physical activities. Children from three inner city comprehensive schools in the Midlands, United Kingdom, participated through questionnaires (n = 381) and semi-structured interviews (n = 62). The results indicated that boys and girls from single parent families spent more time in sedentary activities during the week and at the weekend (P < 0.01) when compared with their intact couple family counterparts. It was identified that children in single-parent families received less parental support due to a lack of time, transport and additional parental responsibilities that created a family environment that encouraged sedentary pursuits. Moreover, the barriers that encouraged sedentary activities also prevented children in single parent families from engaging in lifetime activities during the week. Children from intact couple families recorded more time in lifetime activities than those in single parent families (P < 0.01). Finally, children in two-parent families had more opportunities to engage not only in these activities individually but also in joint activities with their parents, further reinforcing these behaviours.

Ambient Temperature and the Pituitary Hormone Responses to Exercise in Humans

Pituitary hormones have an important role during exercise yet relatively little is known about the stimulus for their release. Body temperature progressively increases during prolonged steady‐state exercise in the heat and we have investigated the role that this may play in the release of prolactin, growth hormone and cortisol (as an indicator of adrenocorticotropic hormone) into the circulation. Fit young male subjects exercised at 73 %O2,max until volitional fatigue at 20 °C and at 35 °C (30 % relative humidity at both temperatures). Rectal temperature and mean skin temperature were monitored and blood samples analysed for lactate, glucose, cortisol, growth hormone and prolactin concentrations. During the first 20 min, core temperature rose continuously and to a similar extent at both temperatures, while mean skin temperature was approximately 4 °C lower during exercise in the cool. Blood glucose concentration was essentially constant throughout the period of exercise while lactate concentration increased in the first 10 min and then remained constant with very similar changes in the two exercise conditions. Prolactin and growth hormone concentrations both increased during the exercise period while the concentration of cortisol declined slightly before rising slightly over the 40 min period. Prolactin release was significantly greater when exercise was carried out in the heat while there was no difference in the release of growth hormone or cortisol in the two conditions. When plotted as a function of rectal temperature, growth hormone concentration showed a linear relationship which was the same at ambient temperatures of 35 °C and 20 °C. Prolactin concentration had a curvilinear relationship with rectal temperature and this differed markedly at the two ambient temperatures. Cortisol concentration showed no dependence on any measure of body temperature. Our results are consistent with some aspect of body temperature being a stimulus for growth hormone and prolactin secretion; however, the precise mechanism clearly differs between the two hormones and we suggest that skin temperature modulates prolactin release, but does not affect the release of growth hormone.

Movement variability in the golf swing

Traditionally, golf biomechanics has focused upon achieving consistency in swing kinematics and kinetics, whilst variability was considered to be noise and dysfunctional. There has been a growing argument that variability is an intrinsic aspect of skilled motor performance and plays a functional role. Two types of variability are described: ‘strategic shot selection’ and ‘movement variability’. In ‘strategic shot selection’, the outcome remains consistent, but the swing kinematics/kinetics (resulting in the desired ball flight) are free to vary; ‘movement variability’ is the changes in swing kinematics and kinetics from trial to trial when the golfer attempts to hit the same shot. These changes will emerge due to constraints of the golfers body, the environment, and the task. Biomechanical research has focused upon aspects of technique such as elite versus non-elite kinematics, kinetics, kinematic sequencing, peak angular velocities of body segments, wrist function, ground reaction forces, and electromyography, mainly in the search for greater distance and clubhead velocity. To date very little is known about the impact of variability on this complex motor skill, and it has yet to be fully researched to determine where the trade-off between functional and detrimental variability lies when in pursuit of enhanced performance outcomes.

A New Progression Scale for Common Lower-Limb Rehabilitation Tasks.

Scarfe, AC, Li, F-X, Reddin, DB, and Bridge, MW. A new progression scale for common lower-limb rehabilitation tasks. J Strength Cond Res 25(3): 612-619, 2011-The treatment of most injuries tends to have similar goals: to minimize initial pain and swelling, restore full range of motion, and return to full strength. One of the key problems is the gap between the traditional rehabilitation modalities and progression to normal locomotive and athletic activities. Closed kinetic chain exercises are a common feature of rehabilitation programs, yet progression of these exercises in a rehabilitation setting has traditionally been based on anecdotal advice, and there is a shortage of empirical evidence. The aim of this study is to use ground reaction force measures to guide progression of closed kinetic chain rehabilitation exercises for active individuals recovering from lower extremity injury. Twenty-four injury-free participants carried out 10 different movements including jumps, squats, and locomotive tasks. Force data collected via a Kistler force platform were used to quantify peak vertical force (Fz), peak vertical force relative to body weight (Fz/BW), and rate of force development (RFD). A Vicon motion analysis system provided kinematic data. There were significant interactions of task and peak Fz, task and peak Fz/BW, and task and RFD. For all force measures, the majority of tasks were significantly different from one another. The effect of kinematic variability was evaluated using the Pearson Correlation coefficient. A clear progression of exercises was seen in both peak Fz and peak Fz/BW, whereas RFD measures showed 3 distinct groups. Combining the data from the measures leads to the grouping the exercises into early, mid, late, and final stages of rehabilitation. We suggest that practitioners use this ranking to prescribe appropriate exercises for particular stages of rehabilitation.