The impact of progressive overload on the proportion and frequency of positive cardio-respiratory fitness responders

The proportion of individuals whose cardio-respiratory fitness change after endurance training does not exceed the test's measurement error can be 40 %. We determined if progressively increasing treadmill run intensity compared to maintaining the same run intensity, improved the responder proportion to a 6-week 20-minute treadmill training regimen. The intervention response standard deviation method estimated the proportion of responders attributable to progressively increasing run intensity. The mixed-effects model demonstrated V̇O2 peak improved significantly more in the progressive versus constant run intensity group. The proportion of V̇O2 peak responses above the smallest worthwhile change attributable to progressively increasing run intensity was 63.6 %.

Coconut Water: A Sports Drink Alternative?

Coconut water is used as an alternative to conventional sports drinks for hydration during endurance cycling; however, evidence supporting its use is limited. This study determined if drinking coconut water compared to a sports drink altered cycling performance and physiology. In a randomized crossover trial, 19 experienced male (n = 15) and female (n = 4) cyclists (age 30 ± 9 years, body mass 79 ± 11 kg, V̇O2 peak 55 ± 8 mL·kg-1·min-1) completed two experimental trials, consuming either a commercially available sports drink or iso-calorific coconut water during 90 min of sub-maximal cycling at 70% of their peak power output, followed by a simulated, variable gradient, 20 km time trial. Blood glucose, lactate, sweat loss, and heart rate were monitored throughout the 90 min of sub-maximal cycling, as well as the time trial performance (seconds) and average power (watts). A repeated measures analysis of variance and effect sizes (Cohen's d) analysis were applied. There were no significant differences (p ≥ 0.05) between the treatments for any of the measured physiological or performance variables. Additionally, the effect size analysis showed only trivial (d ≤ 0.2) differences between the treatments for all the measured variables, except blood glucose, which was lower in the coconut water trial compared to the sports drink trial (d = 0.31). Consuming coconut water had a similar effect on the cycling time trial performance and the physiological responses to consuming a commercially available sports drink.

Stubborn Exercise Responders-Where to Next?

There is a wide variance in the magnitude of physiological adaptations after resistance or endurance training. The incidence of “non” or “poor” responders to training has been reported to represent as high as 40% of the project’s sample. However, the incidence of poor responders to training can be ameliorated with manipulation of either the training frequency, intensity, type and duration. Additionally, global non-response to cardio-respiratory fitness training is eliminated when evaluating several health measures beyond just the target variables as at least one or more measure improves. More research is required to determine if altering resistance training variables results in a more favourable response in individuals with an initial poor response to resistance training. Moreover, we recommend abandoning the term “poor” responders, as ultimately the magnitude of change in cardiorespiratory fitness in response to endurance training is similar in “poor” and “high” responders if the training frequency is subsequently increased. Therefore, we propose “stubborn” responders as a more appropriate term. Future research should focus on developing viable physiological and lifestyle screening tests that identify likely stubborn responders to conventional exercise training guidelines before the individual engages with training. Exerkines, DNA damage, metabolomic responses in blood, saliva and breath, gene sequence, gene expression and epigenetics are candidate biomarkers that warrant investigation into their relationship with trainability. Crucially, viable biomarker screening tests should show good construct validity to distinguish between different exercise loads, and possess excellent sensitivity and reliability. Furthermore “red flag” tests of likely poor responders to training should be practical to assess in clinical settings and be affordable and non-invasive. Early identification of stubborn responders would enable optimization of training programs from the onset of training to maintain exercise motivation and optimize the impact on training adaptations and health.

Defining and assessing an anisotropic delineation margin for modern radiotherapy

PURPOSE

Uncertainty in target volume delineation for modern radiotherapy impacts dosimetry and patient outcomes. Delineation uncertainty is generally overlooked in practice as a source of error, potentially since historically, other uncertainties have been the main focus. This work defined and assessed an anisotropic delineation margin in both polar and spherical coordinate systems in order to account for the spatially varying nature of this uncertainty using a whole breast radiotherapy cohort as a proof of concept.

METHODS

A cohort of 21 whole breast radiotherapy patient datasets with clinical target volumes delineated by eight independent observers was utilized. Patients were divided into categories based on target volume and laterality. An anisotropic delineation margin for each category was determined by multiplying the average standard deviation in observer contours in each category by a factor of two. Standard deviation was determined in both polar and spherical coordinates at angular increments. This anisotropic approach was compared to a conventional clinical approach, where the delineation margin was applied in the cardinal directions only. The assessment of the delineation margin was undertaken by comparing the encompassment of the observer volumes by the target volume with added margin. The extra, presumed healthy tissue included in the margin and the malignant tissue missed by the margin were determined.

RESULTS

The proposed delineation margin is effective at accounting for inter-observer variation, producing >95% coverage of all CTVs for polar, spherical, and Cartesian margins in 82%, 79%, and 92% of cases, respectively. Additionally, <1% malignant tissue was missed for 65%, 70%, and 91% of cases and <37% healthy tissue was included in 95%, 89%, and 97% of cases. A conventional delineation margin approach is most appropriate for small and gold standard target volumes. However, for large target volumes, an anisotropic margin is necessary, producing significantly greater coverage of CTVs, including significantly less presumed healthy tissue and missing significantly less malignant tissue.

CONCLUSIONS

All delineation margin methods that account for target volume and laterality proved to be adequate, with appropriate encompassment of interobserver variation and minimal inclusion of extra excess healthy tissue and exclusion of possible malignant tissue. The anisotropic approach was found to be superior to a conventional approach for target volumes >1400 cm³ only with significantly greater encompassment of interobserver variation, less missed malignant tissue and less included healthy tissue. This methodology has been validated for a whole breast radiotherapy cohort as a proof of concept, however could be applied to other anatomical sites.

SIN, a novel Drosophila protein that associates with the RNA binding protein sex-lethal

Sex-lethal (SXL) is an RNA binding protein that acts as a regulator of both alternative pre-mRNA splicing and translation. Because SXL must sometimes function at some distance from its binding sites, it is believed that it must interact with other proteins. We used a yeast two-hybrid screen to isolate a novel Drosophila protein, SIN (SXL interactor), that interacts specifically with SXL. A direct physical association was demonstrated in vitro, and a single SXL RNA binding domain was sufficient for the interaction. SIN shows a high degree of similarity to a mammalian protein of unknown function. The cytogenetic location of Sin is 78A2-4. The transcript, which is abundant in early embryos, appears to be of maternal origin.

Sex-lethal interactions with protein and RNA. Roles of glycine-rich and RNA binding domains

Sex-lethal (Sxl) is an RNA-binding protein, containing two conserved RNA binding domains (RBDs) and a glycine-rich region, which functions as a regulator of alternative splicing in Drosophila sex determination. Previous work demonstrated that Sxl monomers interact cooperatively upon binding to target RNAs and that the cooperativity depends on the glycine-rich N terminus. Here we use band shift experiments to show that RNA binding patterns are altered when Sxl is combined with other proteins having similar glycine-rich domains, including mammalian heterogeneous nuclear (hn) RNP L and Drosophila Hrb87F (an hnRNP A/B homolog). Direct involvement of the Sxl glycine-rich region in protein interactions was verified by Far-Western analysis. Two interaction domains, the Sxl N terminus and the Sxl first RNA binding domain, were suggested by the yeast two-hybrid assay. In a systematic examination of the RNA binding properties of Sxl domains, it was found that the Sxl termini as well as the RBDs influence RNA binding specificity. Finally, selection of the Sxl optimal binding site (SELEX) confirms the importance of U-runs in the Sxl binding site and suggests a second type of non-U-run target that may be associated with RNA secondary structure.

The Sex-lethal early splicing pattern uses a default mechanism dependent on the alternative 5' splice sites

The Sex-lethal (Sxl) early transcripts have a unique 5' exon and a splicing pattern that differs from that of the late transcripts. While the late transcripts are regulated sex specifically by control of exon 3 inclusion, the early transcripts are not. While the late transcripts include exon 3 by default, the early transcripts skip exon 3. Splicing patterns of a reporter gene that mimics the early transcript, and its variants, were analyzed in Drosophila transformants and tissue culture cells. The results demonstrate that the early, in contrast to the late, splicing pattern is not regulated by stage-specific or sex-specific trans-acting factors, and so the pattern appears to arise from some type of intrinsic splice site preference or compatibility. Inclusion or exclusion of exon 3 is determined by the identity of the upstream 5' splice site region as late or early. The important region of the early exon lies within 233 nucleotides of the immediately adjacent intron.

The Sex-lethal amino terminus mediates cooperative interactions in RNA binding and is essential for splicing regulation

Sex-lethal (Sxl) acts as a binary switch that regulates Drosophila sexual differentiation and dosage compensation and also maintains a stable female state through autoregulation. As part of a cascade of genes that are regulated by sex-specific splicing, Sxl controls the sex-specific splicing of transformer (tra) RNA and also its own RNA. Sxl contains two RNP-CS (RNA-binding) domains and is known to bind tra pre-mRNA near the alternative 3' splice site, thus blocking use of that site to give the female-specific splicing pattern. Here, we test how Sxl protein interacts with Sxl RNA during autoregulation. We show that Sxl not only binds Sxl pre-mRNA near the alternative 3' splice site but also at distant, multiple sites surrounding the Sxl alternative exon. Moreover, Sxl binds cooperatively at these multiple sites. The Sxl amino terminus is essential for the cooperative interaction and is also required for regulatory activity in vivo. It appears that this region of Sxl protein, which resembles regions in some other RNA-binding proteins, is a domain that mediates protein-protein interactions during RNA binding and plays an important role in splicing regulation.

Positive autoregulation of sex-lethal by alternative splicing maintains the female determined state in Drosophila

Sex-lethal is a binary switch gene that controls all aspects of Drosophila sexual dimorphism. It must be active in females and inactive in males. The on/off regulation reflects alternative RNA splicing in which full-length proteins are produced only in females. Here we investigate the role of Sxl in maintaining sexual pathway commitments. By ectopic expression of a female Sxl cDNA in transgenic male flies, we show that Sxl protein induces a rapid switch from male- to female-specific splicing. The ectopically expressed Sxl protein wil trans-activate an endogenous wild-type Sxl gene. This establishes a feedback loop in which Sxl proteins induce their own synthesis by directing the female-specific splicing of Sxl transcripts. We conclude that the female determined state is maintained by Sxl through positive autoregulation, while the male determined state is maintained by default.

Developmental distribution of female-specific Sex-lethal proteins in Drosophila melanogaster

The binary switch gene Sex-lethal (Sxl) must be on in females and off in males to allow the proper elaboration of the appropriate sexual developmental pathway in Drosophila melanogaster. Previous studies suggested a mechanism in which the on/off regulation of Sxl occurs post-transcriptionally at the level of RNA splicing. A critical prediction of this model is that functional Sxl proteins are absent in males but present in females. In this report we show that the expected full-length proteins are only present in female animals. Multiple forms of Sxl protein are found in females, some of which are expressed in a stage- and tissue-specific pattern. Consistent with a role of Sxl proteins in regulating alternate splicing, the proteins are localized in the nucleus where they exhibit a punctate staining pattern. Surprisingly, several minor Sxl proteins appear to be present in specific tissues of both sexes of adults. The possible origin of these species is discussed. We also show that Sxl expression in the early embryo is sex specific and depends on maternal daughterless and zygotic sisterless-b activity in accordance with the established roles of these genes as positive regulators of Sxl. The onset of Sxl expression in the germ line occurs later than that in the soma.

Sex-lethal, a Drosophila sex determination switch gene, exhibits sex-specific RNA splicing and sequence similarity to RNA binding proteins

The switch gene, Sex-lethal (Sxl), controls sexual development and dosage compensation. It must be active in females and inactive in males throughout development. Analysis of Sxl cDNAs shows that this on/off regulation may be explained by differential RNA splicing; only female transcripts appear to encode functional products, whereas all male transcripts contain an exon that truncates the open reading frame. The functional female product shows sequence similarities with ribonucleoproteins, suggesting that it is an RNA binding protein. Thus, we propose that Sxl encodes a factor that interacts with both its own pre-mRNA (accounting for positive autoregulation) and that of downstream genes to confer female-specific splicing. In this way, a single, simple mechanism could account for both the maintenance and expression of the sexually determined state.