Gymnastik- och idrottshögskolan, GIH

Brain-derived neurotrophic factor (BDNF) is essential for neuroplasticity. Exercise caninduce increases in forearm venous plasma and serum BDNF, often assumed to be indicativeof release from the brain. We investigated the effects of exercise on circulating levels of matureBDNF (mBDNF) and its precursor proBDNF. Sixteen healthy, physically fit adults (20–40 years old)cycled for 20 min at 40, 60 and 80% of V˙O2 max, separated by 30 min of rest. BDNF was analysed in blood samples from the brachial artery, internal jugular vein, femoral vein and antecubital vein. Brain/skeletal muscle exchange of BDNF, calculated as arterial-venous differences in BDNF multiplied by blood flow in the middle cerebral artery/common femoral artery, was measured simultaneously with blood sampling. Exercise intensity-dependent increases were observed in blood platelet count, forearm venous serum mBDNF and plasma proBDNF, but not in forearm venous plasma mBDNF. Brain release (or uptake) was not detected for either plasma mBDNF, serum mBDNF or plasma proBDNF. However, muscle uptake of plasma mBDNF and release of plasma proBDNF were observed after high-intensity exercise. Our findings demonstrate that exercise-dependent increases in serum mBDNF are not derived from the brain or the exercised skeletal muscle. Rather, the source of the increase appears to be the increase in platelets that are enriched with mBDNF. Furthermore, in physically fit adults, BDNF is not released from the brain into the bloodstream, after exercise, regardless of exercise intensity. Finally, changes in plasma proBDNF after exercise appear to be dependent on exercised skeletal muscle rather than brain release. KEY POINTS: Previously shown exercise-induced increases in forearm venous brain-derived neurotrophic factor (BDNF) are often assumed to be indicative of release from the brain. We investigated whether exercise-induced changes in forearm venous mature BDNF (mBDNF) and precursor proBDNF are paralleled by concomitant changes in BDNF exchange over the brain and skeletal muscle. We observed exercise intensity-dependent increases in platelet count, forearm venous serum mBDNF and plasma proBDNF, but not in forearm venous plasma mBDNF. We found muscle uptake of plasma mBDNF and release of plasma proBDNF after high-intensity exercise but no exercise intensity-dependent brain exchange of either plasma mBDNF, serum mBDNF or plasma proBDNF. Our findings suggest that acute exercise-induced increases in circulating serum mBDNF may be solely a result of increased platelet count, probably due to splenic platelet release; and that exercised skeletal muscle, and not the brain, responds to high-intensity exercise by releasing plasma proBDNF.

To date, there is no empirical evidence suggesting greater jump heights or cushioned landings when using figure skating (FS) blades of different mass and design. This study examined the effect of lightweight (Gold Seal Revolution from John Wilson) and traditional (Apex Supreme from Jackson Ultima and Volant from Riedell) blades, a new prototype blade with an integrated damping system (damping blade) in two different damping configurations, and running shoes (Runfalcon from Adidas) on kinetics and kinematics during simulated on-ice landings from 0.6 m and maximal countermovement jumps on synthetic ice, and measured dampening properties of the damping blade. Seventeen participants executed trials in the six footwear conditions blinded to the different blades and acted as their own control for statistical comparison. There were no differences between the lightweight and traditional blades on the maximal vertical ground reaction force during the landing. Image analysis showed a damping effect in the damping blade that significantly decreased the landing load for all participants (mean 4.38 ± 0.68 bodyweight) (p ≤ 0.006), on average between 10.1 and 14.3% compared to lightweight and traditional blades (4.87 ± 1.01 to 5.11 ± 0.88 bodyweight). The maximal jump height achieved was the same in all FS blades.

Objective: This study was to investigate alterations in contractile properties of the ankle plantar- and dorsiflexors in post-stroke individuals. The correlation between muscle architecture parameters and contractile properties was also evaluated.

Methods: Eight post-stroke individuals and eight age-matched healthy subjects participated in the study. Participants were instructed to perform maximal isometric contraction (MVC) of ankle plantar- and dorsiflexors at four ankle angles, and isokinetic concentric contraction at two angular velocities. B-mode ultrasound images of gastrocnemius medialis (GM) and tibialis anterior (TA) were collected simultaneously during the MVC and isokinetic measurements. Individualized torque-angle and torque-angular velocity relations were established by fitting the experimental data using a second-order polynomial and a rectangular hyperbola function, respectively. Muscle structure parameters, such as fascicle length, muscle thickness and pennation angle of the GM and TA muscles were quantified.

Results: Post-stroke subjects had significantly smaller ankle plantarflexor and dorsiflexor torques. The muscle structure parameters also showed a significant change in the stroke group, but no significant difference was observed in the TA muscle. A narrowed parabolic shape of the ankle PF torque-fiber length profile with a lower width span was also found in the stroke group.

Conclusion: This study showed that the contractile properties and architecture of ankle muscles in post-stroke individuals undergo considerable changes that may directly contribute to muscle weakness, decreased range of motion, and impaired motion function in individuals after stroke.

PURPOSE: Physical activity (PA) breaks during school lessons have been suggested as a promising strategy to improve working memory performance in children and adolescents. There is a lack of studies investigating the underlying physiological mechanisms of PA on cognition, especially among adolescents. This study aimed to investigate the effects of different types of short frequent PA on adolescents' cognitive task-related changes in cerebral blood flow in the prefrontal cortex (PFC) and working memory performance compared to prolonged sitting.

METHODS: In this randomized crossover study, adolescents visited the laboratory on three different occasions for 80-minute sessions of prolonged sitting interrupted by four breaks for three minutes of simple resistance training (SRA), step-up at a pre-determined pace (STEP), or remaining seated (SOCIAL). Before and after each session, cognitive task-related changes in cerebral blood flow (oxygenated-hemoglobin, Oxy-Hb) during working memory tasks (1-, 2-, 3-back tests) were measured using functional near-infrared spectroscopy in the PFC. Accuracy and reaction time were derived from the working memory tasks. Linear mixed-effect models were used to analyze the data.

RESULTS: A total of 17 students participated (mean age 13.6 years, 11 girls). Significant time x condition interactions were noted for Oxy-Hb in the most demanding working memory task (3-back), with a decrease following prolonged sitting in the SOCIAL condition compared to both the SRA (β 0.18, 95% CI 0.12, 0.24) and the STEP (β 0.11, 95% CI 0.05, 0.17). This was observed in parallel with improvements in reaction time following SRA (β -30.11, 95% CI -59.08, -1.13) and STEP (β -34.29, 95% CI -69.22, 0.63) although this was only significant for the SRA and no improvements in the SOCIAL condition.

CONCLUSION: We found that short frequent PA breaks during prolonged sitting among adolescents can prevent the decrease in cognitive task-related changes in cerebral blood flow that occur following prolonged sitting. This was observed simultaneously with improvements in working memory, indicating that changes in cerebral blood flow could be one factor explaining the effects on working memory. Future studies should investigate the efficacy of implementing these PA breaks in schools.

TRIAL REGISTRATION: Retrospectively registered on 21/09/2020, ClinicalTrial (NCT04552626).

Purpose: Beneficial acute effects of dietary nitrate have been demonstrated on working memory in adults, with changes in cerebral blood flow (CBF) being a potential mechanism. However, these effects have not been studied in adolescents. Moreover, having breakfast compared to skipping may also exhibit positive effects on working memory. Therefore, this randomized crossover trial investigated the acute effects of nitrate and breakfast on working memory and changes in task-related CBF in adolescents.  Methods: This trial will recruit at least 43 adolescents (13–15 years old). There were three experimental breakfast conditions: (1) none, (2) regular, and (3) regular breakfast with high nitrate in the form of concentrated beetroot juice. Working memory (1-, 2-, 3-back tests) and task-related CBF (prefrontal cortex oxygenated and deoxygenated-hemoglobin changes estimated using functional near-infrared spectroscopy) were measured immediately after breakfast and 130 min later. The data collection for this study is ongoing, thus results for 35 adolescents are presented here and due to blinding of the researcher we are unable to report at this time in which condition these effects occurred, but will be revealed by the time of the conference, as well as for the results on changes in CBF.  Results: Preliminary results from the ongoing study showed that from pretest to posttest there was a statistically significant improvement in reaction time in all three conditions for all three n-back tests, but no intervention effects. Accuracy, however, improved from pretest to posttest in only one condition, for all three nback tests (β [95% confidence interval] from linear mixed-effects models with subject as random effect: 1-back 2.8[1.2-4.3], 2-back 2.6[0.9-4.2], 3-back 3.6[2.2-5.0]), and there was a tendency towards an intervention effect between this breakfast condition and another on the accuracy of the 3-back test (P for time-by-condition interaction 0.07).   Conclusions: The results from this study will increase our understanding into the effects of breakfast and its composition (i.e., nitrate-rich) on acutely improving working memory in adolescents and the potential mechanisms. In turn, the results will inform on whether policies on providing breakfast in schools should be considered to improve students' cognitive performance.

BACKGROUND: Inorganic nitrate has been shown to acutely improve working memory in adults, potentially by altering cerebral and peripheral vasculature. However, this remains unknown in adolescents. Furthermore, breakfast is important for overall health and psychological well-being. Therefore, this study will investigate the acute effects of nitrate and breakfast on working memory performance, task-related cerebral blood flow (CBF), arterial stiffness, and psychological outcomes in Swedish adolescents.

METHODS: This randomised crossover trial will recruit at least 43 adolescents (13-15 years old). There will be three experimental breakfast conditions: (1) none, (2) low-nitrate (normal breakfast), and (3) high-nitrate (concentrated beetroot juice with normal breakfast). Working memory (n-back tests), CBF (task-related changes in oxygenated and deoxygenated haemoglobin in the prefrontal cortex), and arterial stiffness (pulse wave velocity and augmentation index) will be measured twice, immediately after breakfast and 130 min later. Measures of psychological factors and salivary nitrate/nitrite will be assessed once before the conditions and at two-time points after the conditions.

DISCUSSION: This study will provide insight into the acute effects of nitrate and breakfast on working memory in adolescents and to what extent any such effects can be explained by changes in CBF. This study will also shed light upon whether oral intake of nitrate may acutely improve arterial stiffness and psychological well-being, in adolescents. Consequently, results will indicate if nitrate intake from beetroot juice or if breakfast itself could acutely improve cognitive, vascular, and psychological health in adolescents, which can affect academic performance and have implications for policies regarding school meals.

TRIAL REGISTRATION: The trial has been prospectively registered on 21/02/2022 at https://doi.org/10.1186/ISRCTN16596056. Trial number: ISRCTN16596056.

Aim

In adults, prolonged periods of sitting have been linked to acute negative effects on vascular structure and function. The aim of this study was to evaluate the acute effects of physical activity (PA) breaks during prolonged sitting on arterial stiffness, cortisol and psychological factors in adolescents.

Methods

Adolescents underwent different short (3-min) breaks starting every 20 min, during 80 min of sitting on three separate days. Breaks were (A) social seated breaks (SOC), (B) low-intensity simple resistance activity PA breaks (SRA) and (C) moderate-intensity step-up PA breaks (STEP). The arterial stiffness measures were augmentation index (AIx), AIx@75 and pulse wave velocity (PWV). Cortisol was measured from saliva. Psychological factors were self-reported.

Results

Eleven girls and six boys (average age 13.6 ± 0.7 years) participated, with average baseline heart rates of 72 ± 11 bpm, systolic/diastolic blood pressure 111 ± 7/64 ± 6 mmHg and cortisol 10.9 ± 5.8 nmoL/L. PWV, cortisol and psychological factors did not change after any of the conditions. AIx@75 increased significantly (4.9 ± 8.7–9.2 ± 13.2) after the STEP intervention compared with SOC and SRA (time × condition p < 0.05).

Conclusion

Arterial stiffness increased after prolonged sitting with frequent, short step-up activity breaks. The results indicate potential important intensity-dependent effects of physical activity on vascular regulation in youth.

Purpose: Physical activity breaks in schools have been suggested as a promising strategy to acutely improve cognitive performance in children and adolescents. Most previous studies have explored the effects of single physical activity bouts, but they are infeasible in a school setting (e.g. long duration/high-intensity or requiring equipment/space). Further, studies investigating the underlying physiological mechanisms in adolescents arel acking. Therefore, the aim of this study was to investigate the effects of short, frequent physical activity breaks of different intensities on adolescents’ working memory (WM) and cerebral blood flow (CBF) during prolonged sitting.

Methods: This randomized crossover study was performed in adolescents (13-15 years of age). In 80-minute sessions, one of the following types of breaks was performed four times in three minutes durations on three different days: simple resistance training (SRA), step-up at a pre-determined pace (STEP), or remaining seated (SOCIAL). Before and after each session, WM (accuracy and reaction time during the 1,2,3-back test) were measured, with simultaneous measurement of task-related CBF (assessed by prefrontal oxygenation using functional near-infrared spectroscopy). Analysis of CBF is ongoing and will be presented at the conference.

Results: A total of 17 students participated (mean age 13.6 years, 11 girls). In the most demanding task (3-back) the following results were seen: improvement in reaction time following SRA (-30.1, p=0.04) and STEP (-34.3 ms, p=0.05) and no improvement following prolonged sitting. We also found a moderating effect (p <0.01) of WM performance at baseline (using a mean split), such that students with poor WM significantly improved their accuracy and reaction time following the higher-intensity breaks (STEP) while students with high performance did not.

Conclusion: We found that implementing physical activity breaks of both moderate and high intensities was beneficial for WM performance. For students with low WM performance, high-intensity breaks were more beneficial. Implementing physical activity breaks during periods of prolonged sitting, such as long school classes could improve the students’ cognitive performance. However, future studies should investigate if these breaks are feasible, acceptable, and beneficial to implement in the school setting.

BACKGROUND: Physical activity breaks are widely being implemented in school settings as a solution to increase academic performance and reduce sitting time. However, the underlying physiological mechanisms suggested to improve cognitive function from physical activity and the frequency, intensity, and duration of the breaks remain unknown. This study will investigate the effects of frequent, short physical activity breaks during prolonged sitting on task-related prefrontal cerebral blood flow, cognitive performance, and psychological factors. Additionally, the moderating and mediating effects of arterial stiffness on changes in cerebral blood flow will be tested.

METHODS: This is a protocol for a randomized crossover study that will recruit 16 adolescents (13-14 years old). Participants will undergo three different conditions in a randomized order, on three separate days, involving sitting 80 min with a different type of break every 17 min for 3 min. The breaks will consist of (1) seated social breaks, (2) simple resistance activities, and (3) step-up activities. Before and after the 80-min conditions, prefrontal cerebral blood flow changes will be measured using functional near-infrared spectroscopy (primary outcome), while performing working memory tasks (1-, 2-, and 3-back tests). Arterial stiffness (augmentation index and pulse wave velocity) and psychological factors will also be assessed pre and post the 80-min interventions.

DISCUSSION: Publication of this protocol will help to increase rigor in science. The results will inform regarding the underlying mechanisms driving the association between physical activity breaks and cognitive performance. This information can be used for designing effective and feasible interventions to be implemented in schools.

TRIAL REGISTRATION: www.ClinicalTrials.gov , NCT04552626 . Retrospectively registered on September 21, 2020.