Trade, growth and the environment

trade policy;economic growth;environment;GATT;general equilibrium;pollution

Biophysical and biomathematical adventures in radiobiology

Highlights of my biophysical and biomathematical adventures in radiobiology is presented. Early adventures involved developing state-vector models'' for specific harmful effects (cell killing, life shortening) of exposure to radiation. More recent adventures led to developing hazard-function models'' for predicting biological effects (e.g., cell killing, mutations, tumor induction) of combined exposure to different toxicants. Hazard-function models were also developed for predicting harm to man from exposure to large radiation doses. Major conclusions derived from the modeling adventures are as follows: (1) synergistic effects of different genotoxic agents should not occur at low doses; (2) for exposure of the lung or bone marrow to large doses of photon radiation, low rates of exposure should be better tolerated than high rates; and (3) for some types of radiation (e.g., alpha particles and fission neutrons), moderate doses delivered at a low rate may be more harmful than the same dose given at a high rate. 53 refs., 7 figs

Exercise with Blood Flow Restriction: An Updated Evidence-Based Approach for Enhanced Muscular Development

A growing body of evidence supports the use of moderate blood flow restriction (BFR) combined with low-load resistance exercise to enhance hypertrophic and strength responses in skeletal muscle. Research also suggests that BFR during low-workload aerobic exercise can result in small but significant morphological and strength gains, and BFR alone may attenuate atrophy during periods of unloading. While BFR appears to be beneficial for both clinical and athletic cohorts, there is currently no common consensus amongst scientists and practitioners regarding the best practice for implementing BFR methods. If BFR is not employed appropriately, there is a risk of injury to the participant. It is also important to understand how variations in the cuff application can affect the physiological responses and subsequent adaptation to BFR training. The optimal way to manipulate acute exercise variables, such as exercise type, load, volume, inter-set rest periods and training frequency, must also be considered prior to designing a BFR training programme. The purpose of this review is to provide an evidence-based approach to implementing BFR exercise. These guidelines could be useful for practitioners using BFR training in either clinical or athletic settings, or for researchers in the design of future studies investigating BFR exercise

The effect of changing player numbers on the physiological responses and time-motion characteristics of a soccer-specific training drill

Soccer-specific training (SST) drills are used to develop physiological adaptations, technical and tactical skills, and provide coaches with greater control of external training load. Despite widespread use, there has been little analysis of SST drills. This study quantified the effect of manipulating player numbers on the physiological demands of an SST drill. Fourteen players completed nine trials (3 × 8, 10, 12 players) of a 4-min SST drill modelled on soccer time-motion data. Physiological intensity measures (heart rate, blood lactate concentration [BLa-], rating of perceived exertion [RPE]) and GPS time-motion data (movement distances and velocities) were collected for each drill. A repeated measures analysis of variance determined significant (p < 0.05) between-drill differences. Results showed variables such as total running distance (TD), mean percentage of maximum heart rate, RPE, and [BLa-] were greater for the 8-player SST drill. The 10-player drill also had a 22% greater TD and 21% higher average speed compared to the 12-player drill, which tended to have a lower activity profile. The 8-player SST drill could be used to develop aerobic capacity and repeat-sprint ability (RSA) because of a higher activity profile. The 10- and 12-player drills would be suited for RSA and sprint acceleration enhancement

A COMPARISON OF IN VIVO CELLULAR RESPONSES TO CS-137 GAMMA RAYS AND 320-KV X RAYS

Research reported here relates to comparing the relative effectiveness of 320-kV X rays compared to Cs-137 gamma rays for two in vivo endpoints in C.B-17 mice after whole-body exposure: (1) cytotoxicity to bone marrow cells and splenocytes evaluated at 24-hours post exposure and (2) bone marrow and spleen reconstitution deficits (repopulation short- falls) evaluated at 6 weeks post exposure. We show that cytotoxicity dose-response rela- tionships for bone marrow cells and splenocytes are complex, involving negative curvature (decreasing slope as dose increases), presumably implicating a mixed cell population com- prised of large numbers of hypersensitive, modestly radiosensitive, and resistant cells. The radiosensitive cells appear to respond with 50% being killed by a dose \u3c 0.5 Gy. The X-ray relative biological effectiveness (RBE), relative to gamma rays, for destroying bone mar- row cells in vivo is \u3e 1, while for destroying splenocytes it is \u3c 1. In contrast, dose-response relationships for reconstitution deficits in the bone marrow and spleen of C.B-17 mice at 6 weeks after radiation exposure were of the threshold type with gamma rays being more effective in causing reconstitution deficit

SMALL γ-RAY DOSES PREVENT RATHER THAN INCREASE LUNG TUMORS IN MICE

We show evidence for low doses of γ rays preventing spontaneous hyperplastic foci and adenomas in the lungs of mice, presumably via activating natural anticancer defenses. The evidence partly relates to a new study we conducted whereby a small number of female A/J mice received 6 biweekly dose fractions (100 mGy per fraction) of γ rays to the total body which prevented the occurrence of spontaneous hyperplastic foci in the lung. We also analyzed data from a much earlier Oak Ridge National Laboratory study involving more than 10,000 female RFMf/Un mice whereby single γ-ray doses from 100 to 1,000 mGy prevented spontaneous lung adenomas. We point out the possibility that the decrease in lung cancer mortality observed in The National Lung Screening Trial Research Team study involving lung tumor screening using low-dose computed tomography (CT) may relate at least in part to low-dose X-rays activating the body’s natural anticancer defenses (i.e., radiation hormesis). This possibility was apparently not recognized by the indicated research team

The efficacy of resistance training in hypoxia to enhance strength and muscle growth: A systematic review and meta-analysis.

Recent studies have reported that resistance training in hypoxia (RTH) may augment muscle size and strength development. However, consensus on the effects of RTH via systematic review and meta-analysis is not yet available. This work aimed to systematically review studies which have investigated using RTH versus normoxic resistance training (NRT) to improve muscular size and strength, and to perform a meta-analysis to determine the effect of RTH on these adaptive parameters. Searches were conducted in PubMed, Web of Science and the Cochrane Library from database inception until 17 June 2017 for original articles assessing the effects of RTH on muscle size and strength versus NRT. The effects on outcomes were expressed as standardized mean differences (SMD). Nine studies (158 participants) reported on the effects of RTH versus NRT for muscle cross-sectional area (CSA) (n = 4) or strength (n = 6). RTH significantly increased CSA (SMD = 0.70, 95% confidence intervals (CI) 0.05, 1.35; p = .04) and strength (SMD = 1.88; 95% CI = 1.20, 2.56; p < .00001). However, RTH did not produce significant change in CSA (SMD = 0.24, 95% CI -0.19, 0.68, p = .27) or strength (SMD = 0.20; 95% CI = -0.27, 0.78; p = .23) when compared to NRT. Although RTH improved muscle size and strength, this protocol did not provide significant benefit over resistance training in normoxia. Nevertheless, this paper identified marked differences in methodologies for implementing RTH, and future research using standardized protocols is therefore warranted.Actividad Física y Deport

Impact of rest-redistribution on fatigue during maximal eccentric knee extensions

Redistributing long inter-set rest intervals into shorter but more frequent rest intervals generally maintains concentric performance, possibly due to improved energy store maintenance. However, eccentric actions require less energy than concentric actions, meaning that shorter but more frequent sets may not affect eccentric actions to the same degree as concentric actions. Considering the increased popularity of eccentric exercise, the current study evaluated the effects of redistributing long inter-set rest periods into shorter but more frequent rest periods during eccentric only knee extensions. Eleven resistance-trained men performed 40 isokinetic unilateral knee extensions at 60°·s-1 with 285 s of total rest using traditional sets (TS; 4 sets of 10 with 95 s inter-set rest) and rest-redistribution (RR; 20 sets of 2 with 15 s inter-set rest). Before and during exercise, muscle oxygenation was measured via near-infrared spectroscopy, and rating of perceived exertion (RPE) was recorded after every 10th repetition. There were no differences between protocols for peak torque (RR, 241.58±47.20 N; TS, 231.64±48.87 N; p=0.396) or total work (RR, 215.26±41.47 J; TS, 209.71±36.02 J; p=0.601), but moderate to large effect sizes existed in later repetitions (6,8,10) with greater peak torque during RR (d=0.66-1.19). For the entire session, RR had moderate effects on RPE (RR, 5.73±1.42; TS, 6.09±1.30; p=0.307; d=0.53) and large effects on oxygen saturation (RR, 5857.4±310.0; TS, 6495.8±273.8; p=0.002, d=2.13). Therefore, RR may maintain peak torque or total work during eccentric exercise, improve oxygen utilization at the muscle, and reduce the perceived effort

Load-velocity relationships and predicted maximal strength: A systematic review of the validity and reliability of current methods

Maximal strength can be predicted from the load-velocity relationship (LVR), although it is important to understand methodological approaches which ensure the validity and reliability of these strength predictions. The aim of this systematic review was to determine factors which influence the validity of maximal strength predictions from the LVR, and secondarily to highlight the effects of these factors on the reliability of predictions. A search strategy was developed and implemented in PubMed, Scopus, Web of Science and CINAHL databases. Rayyan software was used to screen titles, abstracts, and full texts to determine their inclusion/eligibility. Eligible studies compared direct assessments of one-repetition maximum (1RM) with predictions performed using the LVR and reported prediction validity. Validity was extracted and represented graphically via effect size forest plots. Twenty-five eligible studies were included and comprised of a total of 842 participants, three different 1RM prediction methods, 16 different exercises, and 12 different velocity monitoring devices. Four primary factors appear relevant to the efficacy of predicting 1RM: the number of loads used, the exercise examined, the velocity metric used, and the velocity monitoring device. Additionally, the specific loads, provision of velocity feedback, use of lifting straps and regression model used may require further consideration