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Over the past decade, it has been convincingly shown that regularly performing repeated brief supramaximal cycle sprints (sprint interval training [SIT]) is associated with aerobic adaptations and health benefits similar to or greater than with moderate-intensity continuous training (MICT). SIT is often promoted as a time-efficient exercise strategy, but the most commonly studied SIT protocol (4–6 repeated 30-s Wingate sprints with 4 min recovery, here referred to as ‘classic’ SIT) takes up to approximately 30 min per session. Combined with high associated perceived exertion, this makes classic SIT unsuitable as an alternative/adjunct to current exercise recommendations involving MICT. However, there are no indications that the design of the classic SIT protocol has been based on considerations regarding the lowest number or shortest duration of sprints to optimise time efficiency while retaining the associated health benefits. In recent years, studies have shown that novel SIT protocols with both fewer and shorter sprints are efficacious at improving important risk factors of noncommunicable diseases in sedentary individuals, and provide health benefits that are no worse than those associated with classic SIT. These shorter/easier protocols have the potential to remove many of the common barriers to exercise in the general population. Thus, based on the evidence summarised in this current opinion paper, we propose that there is a need for a fundamental change in focus in SIT research in order to move away from further characterising the classic SIT protocol and towards establishing acceptable and effective protocols that involve minimal sprint durations and repetitions.

High-intensity interval training (HIT) has been proposed as a time-efficient alternative to traditional cardiorespiratory exercise training, but is very fatiguing. In this study, we investigated the effects of a reduced-exertion HIT (REHIT) exercise intervention on insulin sensitivity and aerobic capacity. Twenty-nine healthy but sedentary young men and women were randomly assigned to the REHIT intervention (men, n  = 7; women, n  = 8) or a control group (men, n  = 6; women, n  = 8). Subjects assigned to the control groups maintained their normal sedentary lifestyle, whilst subjects in the training groups completed three exercise sessions per week for 6 weeks. The 10-min exercise sessions consisted of low-intensity cycling (60 W) and one (first session) or two (all other sessions) brief ‘all-out’ sprints (10 s in week 1, 15 s in weeks 2–3 and 20 s in the final 3 weeks). Aerobic capacity ( ) and the glucose and insulin response to a 75-g glucose load (OGTT) were determined before and 3 days after the exercise program. Despite relatively low ratings of perceived exertion (RPE 13 ± 1), insulin sensitivity significantly increased by 28% in the male training group following the REHIT intervention ( P  < 0.05). increased in the male training (+15%) and female training (+12%) groups ( P  < 0.01). In conclusion we show that a novel, feasible exercise intervention can improve metabolic health and aerobic capacity. REHIT may offer a genuinely time-efficient alternative to HIT and conventional cardiorespiratory exercise training for improving risk factors of T2D.

Background The efficacy of high-intensity interval training (HIT) as a time-efficient exercise strategy for beneficially modifying risk factors for cardiovascular disease has repeatedly been demonstrated in controlled laboratory settings. However, the effectiveness of HIT in an unsupervised workplace setting has not been investigated. The objective of this study was to use mixed methods to investigate the feasibility, acceptability and effectiveness of a short-duration, high-intensity exercise intervention (REHIT) when applied unsupervised in a workplace setting. Methods Twenty-five office-workers (mean ± SD age: 47 ± 9 y, BMI: 27.5 ± 4.4 kg·m − 2 , V̇O 2 max: 28 ± 7 mL·kg − 1 ·min − 1 ) completed a 6-week REHIT intervention unsupervised in their workplace ( n  = 13, 6 men), or acted as a no-intervention control ( n  = 12, 6 men). The intervention consisted of 2 sessions/week of low-intensity (~ 25 W) cycling interspersed with 2 ‘all-out’ sprints, increasing in duration from 10 to 20 s per sprint over the 6 weeks (total time-commitment: 8:40 min per session). V̇O 2 max was assessed pre- and post-training, whilst questionnaire-based measures of exercise enjoyment, self-efficacy, and acceptability were completed post-training. Eight participants also completed post-intervention semi-structured interviews. Results V̇O 2 max significantly improved in the exercise group (2.25 ± 0.75 L·min − 1 vs. 2.42 ± 0.82 L·min − 1 ; + 7.4%) compared to the control group (2.22 ± 0.72 L·min − 1 vs. 2.17 ± 0.74 L·min − 1 ; − 2.3%; time*intervention interaction effect: p  < 0.01). Participants considered the REHIT intervention acceptable and enjoyable (PACES: 89 ± 17 out of 119) and were confident in their ability to continue to perform REHIT (7.8 ± 1.2 out of 9). Qualitative data revealed that REHIT offered a time-efficient opportunity to exercise, that was perceived as achievable, and which encouraged highly valued post-exercise outcomes (e.g. progress towards health/fitness benefits). Conclusions REHIT could be implemented as a feasible, effective and acceptable exercise intervention in a workplace setting, with a total time-commitment of < 20 min/week. Consideration of certain psycho-social factors and behaviour-change techniques may ensure adherence to the REHIT programme in the long term. Trial registration The study was registered on ClinicalTrials.gov on 07/05/2019 (registration: NCT03941145 ).

PurposeReduced-exertion high-intensity interval training (REHIT) is a genuinely time-efficient exercise intervention that improves aerobic capacity and blood pressure in men with type 2 diabetes. However, the acute effects of REHIT on 24-h glycaemia have not been examined.Methods11 men with type 2 diabetes (mean ± SD: age, 52 ± 6 years; BMI, 29.7 ± 3.1 kg/m2; HbA1c, 7.0 ± 0.8%) participated in a randomised, four-trial crossover study, with continual interstitial glucose measurements captured during a 24-h dietary-standardised period following either (1) no exercise (CON); (2) 30 min of continuous exercise (MICT); (3) 10 × 1 min at ~ 90 HRmax (HIIT; time commitment, ~ 25 min); and (4) 2 × 20 s ‘all-out’ sprints (REHIT; time commitment, 10 min).ResultsCompared to CON, mean 24-h glucose was lower following REHIT (mean ± 95%CI: − 0.58 ± 0.41 mmol/L, p = 0.008, d = 0.55) and tended to be lower with MICT (− 0.37 ± 0.41 mmol/L, p = 0.08, d = 0.35), but was not significantly altered following HIIT (− 0.37 ± 0.59 mmol/L, p = 0.31, d = 0.35). This seemed to be largely driven by a lower glycaemic response (area under the curve) to dinner following both REHIT and MICT (− 11%, p < 0.05 and d > 0.9 for both) but not HIIT (− 4%, p = 0.22, d = 0.38). Time in hyperglycaemia appeared to be reduced with all three exercise conditions compared with CON (REHIT: − 112 ± 63 min, p = 0.002, d = 0.50; MICT: -115 ± 127 min, p = 0.08, d = 0.50; HIIT − 125 ± 122 min, p = 0.04, d = 0.54), whilst indices of glycaemic variability were not significantly altered.ConclusionREHIT may offer a genuinely time-efficient exercise option for improving 24-h glycaemia in men with type 2 diabetes and warrants further study.

Isolated spherical carbonate concretions observed in marine sediments are fascinating natural objet trouve because of their rounded shapes and distinct sharp boundaries. They occur in varied matrices and often contain well preserved fossils. The formation process of such concretions has been explained by diffusion and rapid syn-depositional reactions with organic solutes and other pore water constituents. However, the rates, conditions and formation process of syngenetic spherical concretions are still not fully clear. Based on the examination of different kinds of spherical concretions from several locations in Japan, a diffusion based growth diagram was applied to define the generalized growth conditions of spherical concretions formed around decaying organic matter. All analytical data imply that the spherical concretions formed very rapidly, at least three to four orders of magnitude faster than previously estimated timescales. The values indicate that spherical concretions are preferentially grown within clay- to silt-grade marine sediments deposited in relatively deep (a few tens of metres) environments dominated by diffusive solute transport, very early in diagenesis.

Introduction Whether acute caffeine supplementation can offset the negative effects of one-night of partial sleep deprivation (PSD) on endurance exercise performance is currently unknown. Methods Ten healthy recreational male runners (age: 27 ± 6 years; V ˙ O 2 max : 61 ± 9 mL/kg/min) completed 4 trials in a balanced Latin square design, which were PSD + caffeine (PSD-Caf), PSD + placebo (PSD-Pla), normal sleep (NS) + caffeine (NS-Caf) and NS + placebo (NS-Pla). 3 and 8 h sleep windows were scheduled in PSD and NS, respectively. 10-km treadmill time trial (TT) performance was assessed 45 min after caffeine (6 mg/kg/body mass)/placebo supplementation in the morning following PSD/NS. Blood glucose, lactate, free fatty acid and glycerol were measured at pre-supplementation, pre-exercise and after exercise. Results PSD resulted in compromised TT performance compared to NS in the placebo conditions by 5% (51.9 ± 7.7 vs. 49.4 ± 6.9 min, p  = 0.001). Caffeine improved TT performance compared to placebo following both PSD by 7.7% (PSD-Caf: 47.9 ± 7.3 min vs. PSD-Pla: 51.9 ± 7.7 min, p  = 0.007) and NS by 2.8% (NS-Caf: 48.0 ± 6.4 min vs. NS-Pla: 49.4 ± 6.9 min, p  = 0.049). TT performance following PSD-Caf was not different from either NS-Pla or NS-Caf ( p  = 0.185 and p  = 0.891, respectively). Blood glucose, lactate, and glycerol concentrations at post-exercise, as well as heart rate and the speed/RPE ratio during TT, were higher in caffeine trials compared to placebo. Conclusions Caffeine supplementation offsets the negative effects of one-night PSD on 10-km running performance.

Regular physical activity reduces the risk of several site-specific cancers in humans and suppresses tumour growth in animal models. The mechanisms through which exercise reduces tumour growth remain incompletely understood, but an intriguing and accumulating body of evidence suggests that the incubation of cancer cells with post-exercise serum can have powerful effects on key hallmarks of cancer cell behaviour in vitro. This suggests that exercise can impact tumour biology through direct changes in circulating proteins, RNA molecules and metabolites. Here, we provide a comprehensive narrative overview of what is known about the effects of exercise-conditioned sera on in vitro cancer cell behaviour. In doing so, we consider the key limitations of the current body of literature, both from the perspective of exercise physiology and cancer biology, and we discuss the potential in vivo physiological relevance of these findings. We propose key opportunities for future research in an area that has the potential to identify key anti-oncogenic protein targets and optimise physical activity recommendations for cancer prevention, treatment and survivorship.

The magnitude of the benefi cial increase in plasma interleukin-6 (IL-6) with exercise is greater with continuous exercise of higher intensity and longer duration. However, it is unknown whether a greater volume of supramaximal interval exercise also enhances the IL-6 response. Therefore, the aim of this study was to compare the eff ects of two sprint interval training (SIT) protocols involving different volumes of sprint exercise on plasma IL-6 levels. Nine healthy young men (age: 24±4 y, BMI: 23.3±3.1 kg·m-2, V̇ O2max: 42±6 mL·kg-1·min-1) completed three experimental trials in randomised order, including 'classic' SIT (4x30-s 'all-out' cycle sprints within a 22-min session), reduced-exertion high-intensity interval training (REHIT; 2x20-s 'all-out' cycle sprints within a 10-min session), and a control condition (seated rest). Blood samples were collected before exercise and at 0-, 30-, and 90-min post-exercise, and analyzed for lactate and IL-6. Blood lactate levels peaked directly post-SIT (1.5±0.2 mM to 11.9±2.5 mM; p<.001) and REHIT (1.7±0.4 to 9.1±3.1 mM; p<.001). Plasma IL-6 levels peaked 30-min post-exercise (0.84±0.12 to 1.31±0.17 pg·mL-1 for SIT, p=.003; 0.75±0.09 to 1.18±0.36 pg·mL-1 for REHIT, p=.028). Compared to the con-trol trial, IL-6 iAUC was signifi cantly higher for both SIT (p=.002) and REHIT (p=.013), with no signifi cant diff erence between SIT and REHIT. In conclusion, we demonstrate that the increase in plasma IL-6 levels is similar for the two SIT protocols involving a 3-fold diff erence in sprint exercise volume (120 s vs. 40 s). Our data provide support for a possible role of glycogenolysis in the IL-6 response to SIT.

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depositional chemical processes by which the isolated spherical shape developed and the associated carbon sources are little known. Here we present evidence that spherical carbonate concretions (diameters φ : 14 ~ 37 mm) around tusk-shells ( Fissidentalium spp.) were formed within weeks or months following death of the organism by the seepage of fatty acid from decaying soft body tissues. Characteristic concentrations of carbonate around the mouth of a tusk-shell reveal very rapid formation during the decay of organic matter from the tusk-shell. Available observations and geochemical evidence have enabled us to construct a ‘Diffusion-growth rate cross-plot’ that can be used to estimate the growth rate of all kinds of isolated spherical carbonate concretions identified in marine formations. Results shown here suggest that isolated spherical concretions that are not associated with fossils might also be formed from carbon sourced in the decaying soft body tissues of non-skeletal organisms with otherwise low preservation potential.

Isolated spherical carbonate concretions are frequently observed in finer grained marine sediments of widely varying geological age. Recent studies on various kinds of spherical carbonate (CaCO 3 ) concretions revealed that they formed very rapidly under tightly constrained conditions. However, the formation ages of the isolated spherical carbonate concretions have never been determined. Here we use 87 Sr/ 86 Sr ratios to determine the ages of these spherical concretions. The studied concretions formed in the Yatsuo Group of Miocene age in central Japan. Some formed post-mortem around tusk-shells ( Fissidentalium spp.), while other concretions have no shell fossils inside. The deformation of sedimentary layers around the concretions, combined with geochemical analyses, reveal that Sr was incorporated into the CaCO 3 concretions during their rapid formation. Strontium isotopic stratigraphy using 87 Sr/ 86 Sr ratios of all concretions indicates an age of 17.02 ± 0.27 Ma, with higher accuracy than the ages estimated using micro-fossils from the Yatsuo Group. The results imply that the 87 Sr/ 86 Sr ratio of isolated spherical carbonate concretions can be applied generally to determine the numerical ages of marine sediments, when concretions formed soon after sedimentation. The 87 Sr/ 86 Sr age determinations have high accuracy, even in cases without any fossils evidence.