Variable, but not free-weight, resistance back squat exercise potentiates jump performance following a comprehensive task-specific warm-up

Studies examining acute, high-speed movement performance enhancement following intense muscular contractions (frequently called "post-activation potentiation"; PAP) often impose a limited warm-up, compromizing external validity. In the present study, the effects on countermovement vertical jump (CMJ) performance of back squat exercises performed with or without elastic bands during warm-up were compared. After familiarization, fifteen active men visited the laboratory on two occasions under randomized, counterbalanced experimental squat warm-up conditions: (a) free-weight resistance (FWR) and (b) variable resistance (VR). After completing a comprehensive task-specific warm-up, three maximal CMJs were performed followed by three back squat repetitions completed at 85% of 1-RM using either FWR or VR Three CMJs were then performed 30 seconds, 4 minutes, 8 minutes, and 12 minutes later. During CMJ trials, hip, knee, and ankle joint kinematics, ground reaction force data and vastus medialis, vastus lateralis, and gluteus maximus electromyograms (EMG) were recorded simultaneously using 3D motion analysis, force platform, and EMG techniques, respectively. No change in any variable occurred after FWR (P > 0.05). Significant increases (P < 0.05) were detected at all time points following VR in CMJ height (5.3%-6.5%), peak power (4.4%-5.9%), rate of force development (12.9%-19.1%), peak concentric knee angular velocity (3.1%-4.1%), and mean concentric vastus lateralis EMG activity (27.5%-33.4%). The lack of effect of the free-weight conditioning contractions suggests that the comprehensive task-specific warm-up routine mitigated any further performance augmentation. However, the improved CMJ performance following the use of elastic bands is indicative that specific alterations in force-time properties of warm-up exercises may further improve performance

Sustainable Phosphorus Loadings from Effective and Cost-Effective Phosphorus Management Around the Baltic Sea

Nutrient over-enrichment of the Baltic Sea, accompanied by intensified algal blooms and decreasing water clarity, has aroused widespread concern in the surrounding countries during the last four decades. This work has used a well-tested dynamic mass-balance model to investigate which decrease in total phosphorus loading would be required to meet the environmental goal to restore the trophic state in the Baltic Sea to pre-1960s levels. Furthermore, the extent to which various abatement options may decrease the phosphorus loading in a cost-effective manner has been studied. Upgrading urban sewage treatment in the catchment could, alone or in combination with banning phosphates in detergents, be sufficient to meet the set environmental goal, at an estimated annual basin-wide cost of 0.21–0.43 billion euro. Such a plan would potentially decrease the total phosphorus loading to the Baltic Sea with 6,650–10,200 tonnes per year

Asymptomatic Achilles tendon pathology is associated with a central fat distribution in men and a peripheral fat distribution in women: a cross sectional study of 298 individuals

<p>Abstract</p> <p>Background</p> <p>Adiposity is a modifiable factor that has been implicated in tendinopathy. As tendon pain reduces physical activity levels and can lead to weight gain, associations between tendon pathology and adiposity must be studied in individuals without tendon pain. Therefore, the purpose of this study was to determine whether fat distribution was associated with asymptomatic Achilles tendon pathology.</p> <p>Methods</p> <p>The Achilles tendons of 298 individuals were categorised as normal or pathological using diagnostic ultrasound. Fat distribution was determined using anthropometry (waist circumference, waist hip ratio [WHR]) and dual-energy x-ray absorptiometry.</p> <p>Results</p> <p>Asymptomatic Achilles tendon pathology was more evident in men (13%) than women (5%) (p = 0.007). Men with tendon pathology were older (50.9 ± 10.4, 36.3 ± 11.3, p < 0.001), had greater WHR (0.926 ± 0.091, 0.875 ± 0.065, p = 0.039), higher android/gynoid fat mass ratio (0.616 ± 0.186, 0.519 ± 0.142, p = 0.014) and higher upper-body/lower body fat mass ratio (2.346 ± 0.630, 2.022 ± 0.467, p = 0.013). Men older than 40 years with a waist circumference >83 cm had the greatest prevalence of tendon pathology (33%). Women with tendon pathology were older (47.4 ± 10.0, 36.0 ± 10.3, p = 0.008), had less total fat (17196 ± 3173 g, 21626 ± 7882 g, p = 0.009), trunk fat (7367 ± 1662 g, 10087 ± 4152 g, p = 0.003) and android fat (1117 ± 324 g, 1616 ± 811 g, p = 0.005). They had lower central/peripheral fat mass ratios (0.711 ± 0.321 g, 0.922 ± 0.194 g, p = 0.004) than women with normal tendons. Women with tendon pathology were more often menopausal (63%, 13%, p = 0.002).</p> <p>Conclusions</p> <p>Men with Achilles tendon pathology were older and had a central fat distribution. Women with tendon pathology were older and had a peripheral fat distribution. An interaction between age and waist circumference was observed among men.</p

Patellar tendon properties distinguish elite from non-elite soccer players and are related to peak horizontal but not vertical power

Purpose: The aims of our study were to investigate differences in tendon properties between elite and non-elite soccer players, and to establish whether tendon properties were related to power assessed during unilateral jumps in different directions. Methods: Elite (n=16; age, 18.1 ± 1.0yrs) and non-elite (n=13; age, 22.3 ± 2.7yrs) soccer players performed three repetitions of each type (unilateral vertical, unilateral horizontal-forward and unilateral medial) of countermovement jump (CMJ) on a force plate. Patellar tendon (PT) cross-sectional area (CSA), elongation, stiffness and Young’s modulus (measured at the highest common force interval) were assessed with ultrasonography and isokinetic dynamometry. Results: Elite soccer players demonstrated greater PT elongation (6.83±1.87 vs. 4.92±1.88 mm, P=0.011) and strain (11.73±3.25 vs. 8.38±3.06 %, P=0.009) than non-elite. Projectile range and peak horizontal power during unilateral horizontal-forward CMJ correlated positively with tendon elongation (r=0.657 and 0.693, P<0.001) but inversely with Young’s modulus (r=-0.376 and -0.402, P=0.044 and 0.031). Peak medial power during unilateral medial CMJ correlated positively with tendon elongation (r=0.658, P=<0.001) but inversely with tendon stiffness (r=-0.368, P=0.050). No tendon property correlated with unilateral vertical CMJ performance (r≤0.168; P≥0.204). Conclusions: Patellar tendon strain was greater in elite vs. non-elite soccer players and can therefore be considered an indicator of elite soccer playing status. Moreover, a more compliant patellar tendon appears to facilitate unilateral horizontal-forward and medial, but not vertical CMJ performance in soccer players. These findings should be considered when prescribing the detail of talent selection and development protocols related to direction-specific power in elite soccer players

The influence of muscular action on bone strength via exercise

Mechanical stimuli influence bone strength, with internal muscular forces thought to be the greatest stressors of bone. Consequently, the effects of exercise in improving and maintaining bone strength have been explored in a number of interventional studies. These studies demonstrate a positive effect of high-impact activities (i.e. where large muscle forces are produced) on bone strength, with benefits being most pronounced in interventions in early pubertal children. However, current studies have not investigated the forces acting on bones and subsequent deformation, preventing the development of optimised and targeted exercise interventions. Similarly, the effects of number and frequency of exercise repetitions and training sessions on bone accrual are unexplored. There are conflicting results as to gender effects on bone response to exercise, and the effects of age and starting age on the osteogenic effects of exercise are not well known. It also appears that exercise interventions are most effective in physically inactive people or counteracting conditions of disuse such as bed rest. Bone strength is only one component of fracture risk, and it may be that exercise resulting in improvements in, e.g., muscle force/power and/or balance is more effective than those whose effects are solely osteogenic. In summary, exercise is likely to be an effective tool in maintaining bone strength but current interventions are far from optimal. © Springer Science+Business Media 2013

Interventions outside the workplace for reducing sedentary behaviour in adults under 60 years of age

Background Adults spend a majority of their time outside the workplace being sedentary. Large amounts of sedentary behaviour increase the risk of type 2 diabetes, cardiovascular disease, and both all‐cause and cardiovascular disease mortality. Objectives Primary • To assess effects on sedentary time of non‐occupational interventions for reducing sedentary behaviour in adults under 60 years of age Secondary • To describe other health effects and adverse events or unintended consequences of these interventions • To determine whether specific components of interventions are associated with changes in sedentary behaviour • To identify if there are any differential effects of interventions based on health inequalities (e.g. age, sex, income, employment) Search methods We searched CENTRAL, MEDLINE, Embase, Cochrane Database of Systematic Reviews, CINAHL, PsycINFO, SportDiscus, and ClinicalTrials.gov on 14 April 2020. We checked references of included studies, conducted forward citation searching, and contacted authors in the field to identify additional studies. Selection criteria We included randomised controlled trials (RCTs) and cluster RCTs of interventions outside the workplace for community‐dwelling adults aged 18 to 59 years. We included studies only when the intervention had a specific aim or component to change sedentary behaviour. Data collection and analysis Two review authors independently screened titles/abstracts and full‐text articles for study eligibility. Two review authors independently extracted data and assessed risk of bias. We contacted trial authors for additional information or data when required. We examined the following primary outcomes: device‐measured sedentary time, self‐report sitting time, self‐report TV viewing time, and breaks in sedentary time. Main results We included 13 trials involving 1770 participants, all undertaken in high‐income countries. Ten were RCTs and three were cluster RCTs. The mean age of study participants ranged from 20 to 41 years. A majority of participants were female. All interventions were delivered at the individual level. Intervention components included personal monitoring devices, information or education, counselling, and prompts to reduce sedentary behaviour. We judged no study to be at low risk of bias across all domains. Seven studies were at high risk of bias for blinding of outcome assessment due to use of self‐report outcomes measures. Primary outcomes Interventions outside the workplace probably show little or no difference in device‐measured sedentary time in the short term (mean difference (MD) ‐8.36 min/d, 95% confidence interval (CI) ‐27.12 to 10.40; 4 studies; I² = 0%; moderate‐certainty evidence). We are uncertain whether interventions reduce device‐measured sedentary time in the medium term (MD ‐51.37 min/d, 95% CI ‐126.34 to 23.59; 3 studies; I² = 84%; very low‐certainty evidence) We are uncertain whether interventions outside the workplace reduce self‐report sitting time in the short term (MD ‐64.12 min/d, 95% CI ‐260.91 to 132.67; I² = 86%; very low‐certainty evidence). Interventions outside the workplace may show little or no difference in self‐report TV viewing time in the medium term (MD ‐12.45 min/d, 95% CI ‐50.40 to 25.49; 2 studies; I² = 86%; low‐certainty evidence) or in the long term (MD 0.30 min/d, 95% CI ‐0.63 to 1.23; 2 studies; I² = 0%; low‐certainty evidence). It was not possible to pool the five studies that reported breaks in sedentary time given the variation in definitions used. Secondary outcomes Interventions outside the workplace probably have little or no difference on body mass index in the medium term (MD ‐0.25 kg/m², 95% CI ‐0.48 to ‐0.01; 3 studies; I² = 0%; moderate‐certainty evidence). Interventions may have little or no difference in waist circumference in the medium term (MD ‐2.04 cm, 95% CI ‐9.06 to 4.98; 2 studies; I² = 65%; low‐certainty evidence). Interventions probably have little or no difference on glucose in the short term (MD ‐0.18 mmol/L, 95% CI ‐0.30 to ‐0.06; 2 studies; I² = 0%; moderate‐certainty evidence) and medium term (MD ‐0.08 mmol/L, 95% CI ‐0.21 to 0.05; 2 studies, I² = 0%; moderate‐certainty evidence) Interventions outside the workplace may have little or no difference in device‐measured MVPA in the short term (MD 1.99 min/d, 95% CI ‐4.27 to 8.25; 4 studies; I² = 23%; low‐certainty evidence). We are uncertain whether interventions improve device‐measured MVPA in the medium term (MD 6.59 min/d, 95% CI ‐7.35 to 20.53; 3 studies; I² = 70%; very low‐certainty evidence). We are uncertain whether interventions outside the workplace improve self‐reported light‐intensity PA in the short‐term (MD 156.32 min/d, 95% CI 34.34 to 278.31; 2 studies; I² = 79%; very low‐certainty evidence). Interventions may have little or no difference on step count in the short‐term (MD 226.90 steps/day, 95% CI ‐519.78 to 973.59; 3 studies; I² = 0%; low‐certainty evidence) No data on adverse events or symptoms were reported in the included studies. Authors' conclusions Interventions outside the workplace to reduce sedentary behaviour probably lead to little or no difference in device‐measured sedentary time in the short term, and we are uncertain if they reduce device‐measured sedentary time in the medium term. We are uncertain whether interventions outside the workplace reduce self‐reported sitting time in the short term. Interventions outside the workplace may result in little or no difference in self‐report TV viewing time in the medium or long term. The certainty of evidence is moderate to very low, mainly due to concerns about risk of bias, inconsistent findings, and imprecise results. Future studies should be of longer duration; should recruit participants from varying age, socioeconomic, or ethnic groups; and should gather quality of life, cost‐effectiveness, and adverse event data. We strongly recommend that standard methods of data preparation and analysis are adopted to allow comparison of the effects of interventions to reduce sedentary behaviour

Differential contributions of ankle plantarflexors during submaximal isometric muscle action: a PET and EMG study

The objective of this study was to investigate the relative contributions of superficial and deep ankle plantarflexors during repetitive submaximal isometric contractions using surface electromyography (SEMG) and positron emission tomography (PET). Myoelectric signals were obtained from twelve healthy volunteers (27.3 ± 4.2 yrs). A tracer ([18F]-FDG) was injected during the exercise and PET scanning was done immediately afterwards. The examined muscles included soleus (Sol), medial gastrocnemius (MG), lateral gastrocnemius (LG), and flexor hallucis longus (FHL). It was found that isometric maximal voluntary contraction (MVC) force, muscle glucose uptake (GU) rate, and SEMG of various plantarflexors were comparable bilaterally. In terms of %EMG MVC, FHL and MG displayed the highest activity (∼34%), while LG (∼21%) had the lowest activity. Cumulative SEMG from all parts of the triceps surae (TS) muscle accounted for ∼70% of the combined EMG signal of all four plantarflexors. As for GU, the highest quantity was observed in MG (2.4 ± 0.8 μmol * 100 g−1 * min−1), whereas FHL (1.8 ± 0.6 μmol * 100 g−1 * min−1) had the lowest uptake. Cumulative GU of TS constituted nearly 80% of the combined GU. The findings of this study provide valuable reference for studies where individual muscle contributions are estimated using models and simulations