Effects of competition outcome on testosterone concentrations in humans: An updated meta-analysis

A contribution to a special issue on Hormones and Human Competition.Since Archer's (2006) influential meta-analysis, there has been a major increase in the number of studies investigating the effect of competition outcome on testosterone reactivity patterns in humans. Despite this increased research output, there remains debate as to whether competition outcome modulates testosterone concentrations. The present paper examines this question using a meta-analytic approach including papers published over the last 35 years. Moreover, it provides the first meta-analytic estimate of the effect of competition outcome on testosterone concentrations in women. Results from a meta-analysis involving 60 effect sizes and > 2500 participants indicated that winners of a competition demonstrated a larger increase in testosterone concentrations relative to losers (D = 0.20)—an effect that was highly heterogeneous. This ‘winner-loser’ effect was most robust in studies conducted outside the lab (e.g., in sport venues) (D = 0.43); for studies conducted in the lab, the effect of competition outcome on testosterone reactivity patterns was relatively weak (D = 0.08), and only found in studies of men (D = 0.15; in women: D = − 0.04). Further, the 'winner-loser' effect was stronger among studies in which pre-competition testosterone was sampled earlier than (D = 0.38, after trim and fill correction) rather than within (D = 0.09) 10 min of the start of the competition. Therefore, these results also provide important insight regarding study design and methodology, and will be a valuable resource for researchers conducting subsequent studies on the 'winner loser' effect.     

Promoting effect of Fusarium oxysporum [f.sp. strigae] on abundance of nitrifying prokaryotes in a maize rhizosphere across soil types

The integrated application of resistant crop varieties with biological control agents (BCAs) such as the Fusarium oxysporum [f.sp. strigae] strain “Foxy-2” has shown to be effective in fighting off the weed Striga hermonthica which is parasitic to several cereals cultivated in Sub-Saharan Africa (Schaub et al., 2006; Venne et al., 2009). “Foxy-2” proliferates in the rhizosphere and has been mainly studied for its virulence and mode of action. Contrary, no understanding is available regarding its interactions with key rhizosphere microorganisms steering relevant nutrient cycles in soils including nitrogen (N). In this study, we tested the hypothesis that “Foxy-2” displaces indigenous prokaryotic, N cycling communities in the maize rhizosphere due to competition for organic resources. Consequently, we evaluated if the application of an N-rich organic residue (i.e., Tithonia diversifolia with C/N ratio = 13, lignin content = 8.9%, polyphenol content = 1.7%) compensates these presumed competition effects. In a rhizobox experiment, quantitative polymerase chain reaction was used to follow the response of rhizosphere ammonia-oxidizing archaea (AOA) and bacteria (AOB) as well as total bacteria and archaea following “Foxy-2” inoculation in two physico-chemically contrasting soils (sandy Ferric Alisol versus clayey Humic Nitisol). Soils were treated with or without “Foxy-2”, S. hermonthica seeds, and T. diversifolia residues. Contrary to our expectations, we observed a distinct soil texture dependent, promoting effect of “Foxy-2” on rhizosphere prokaryotes. Abundance of AOA and total prokaryotic communities increased in response to “Foxy-2” in the sandy soil, while AOB remained unaffected. This effect on AOA was accelerated when T. diversifolia residues were incorporated. Further, in the clayey soil, AOA abundance was promoted when exposed to S. hermonthica infestation of maize. This suggested their capability to adapt to this biotic stress situation. It was concluded that “Foxy-2” did not pose a negative effect on targeted indigenous microorganisms, but the underlying mechanisms for the observed promoting effect of AOA abundance by “Foxy-2” inoculation are yet to be understood.     

Age-independent increases in male salivary testosterone during horticultural activity among Tsimane forager-farmers

Testosterone plays an important role in mediating male reproductive trade-offs in many vertebrate species, augmenting muscle and influencing behavior necessary for male–male competition and mating-effort. Among humans, testosterone may also play a key role in facilitating male provisioning of offspring as muscular and neuromuscular performance is deeply influenced by acute changes in testosterone. This study examines acute changes in salivary testosterone among 63 Tsimane men ranging in age from 16 to 80 (mean 38.2) years during one-hour bouts of tree-chopping while clearing horticultural plots. The Tsimane forager-horticulturalists living in the Bolivian Amazon experience high energy expenditure associated with food production, have high levels of parasites and pathogens, and display significantly lower baseline salivary testosterone than age-matched US males. Mixed-effects models controlling for BMI and time of specimen collection reveal increased salivary testosterone (p < 0.001) equivalent to a 48.6% rise, after one hour of tree chopping. Age had no effect on baseline (p = 0.656) or change in testosterone (p = 0.530); self-reported illness did not modify testosterone change (p = 0.488). A comparison of these results to the relative change in testosterone during a competitive soccer tournament in the same population reveals larger relative changes in testosterone following resource production (tree chopping), compared to competition (soccer). These findings highlight the importance of moving beyond a unidimensional focus on changes in testosterone and male–male aggression to investigate the importance of testosterone–behavior interactions across additional male fitness-related activities. Acutely increased testosterone during muscularly intensive horticultural food production may facilitate male productivity and provisioning.     

Competition-related testosterone,cortisol, and perceived personal success in recreational women athletes

Thirty-five women participating in one or more intramural flag-football games provided saliva samples before, immediately after, and 10 min after competition and completed an after-competition questionnaire appraising their own performance during the game. As seen in other studies of elite athletes, these recreational athletes, on average, showed significant elevations in testosterone (T) and cortisol (C) across the competition period – the “competition effect”. In winners and losers, T levels at all time points measured were positively related to athletes' appraisals of their own individual performance. Results from this study show that the competition effect for T and C is evident in recreational women athletes and provide preliminary evidence about the relationship between cognitive appraisal and competition-related T levels.     

Comparison of clear and narrow outcomes on testosterone levels in social competition

A contribution to a special issue on Hormones and Human Competition.Social competition is associated with marked emotional, behavioral and hormonal responses, including changes in testosterone levels. The strength and direction of these responses is often modulated by levels of other hormones (e.g. cortisol) and depends on psychological factors – classically, the objective outcome of a competition (win vs. loss) but also, hypothetically, the closeness of that outcome (e.g. decisive victory vs. close victory). We manipulated these two aspects of a social contest among male participants (N = 166), to investigate how testosterone and affect fluctuated as a function of clear vs. narrow wins and clear vs. narrow losses. We found that losing a competition by a small margin (a narrow loss) was experienced as more pleasant than a clear loss. Among individuals with higher levels of basal cortisol, winning the competition by a narrow margin was associated with a decrease in testosterone levels. These findings are discussed within the framework of the status instability hypothesis and the growing literature on how situational and physiological factors modulate testosterone reactivity to social contests.     

Sex hormone levels in the brain of d-aspartate-treated rats

d-Aspartate (d-Asp) is an endogenous amino acid present in the central nervous system and endocrine glands of various animal taxa. d-Asp is implicated in neurotransmission, physiology of learning, and memory processes. In gonads, it plays a crucial role in sex hormone synthesis. We have investigated the effects of chronic (30 days d-Asp drinking solution) and acute (i.p. injection of 2 μmol/g bw d-Asp) treatments on sex steroid synthesis in rat brain. Furthermore, to verify the direct effect of d-Asp on neurosteroidogenic enzyme activities, brain homogenates were incubated with different substrates (cholesterol, progesterone, or testosterone) with or without the addition of d-Asp. Enzyme activities were measured by evaluating the in vitro conversion rate of (i) cholesterol to progesterone, testosterone, and 17β-estradiol, (ii) progesterone to testosterone and 17β-estradiol, (iii) testosterone to 17β-estradiol. We found that d-Asp oral administration produced an increase of approximately 40% in progesterone, 110% in testosterone, and 35% in 17β-estradiol. Similarly, the results of the acute experiment showed that at 30 min after d-Asp treatment, the progesterone, testosterone, and 17β-estradiol levels increased by 29–35%, and at 8 h they further increased by a 100% increment. In vitro experiments demonstrate that the addition of d-Asp to brain homogenate + substrate induces a significant increase in progesterone, testosterone and 17β-estradiol suggesting that the amino acid upregulates the local activity of steroidogenic enzymes.     

Stress as adaptation? A test of the adaptive boost hypothesis among Batswana men

Many studies have found elevated cortisol linked to negative events (“stress”) and subsequent negative outcomes, such as reduced immunity and stunted growth, leading to the conclusion that high cortisol is “bad.” However, a growing number of studies have found more advantaged groups showing relatively elevated cortisol. For example, higher morning cortisol followed by a steeper diurnal decline among Caucasians compared to ethnic minorities has been interpreted as a context-specific “adaptive boost” to meet daily demands. We tested the adaptive boost hypothesis using data on socioeconomic status, depressive affect and salivary cortisol among adult men (n = 32) in Botswana. Three findings emerged: (i) depressive affect was associated with lower morning cortisol (r = ? 0.43, p = 0.014); (ii) depressive affect was associated with a diurnal increase in cortisol when comparing morning and evening samples (r = 0.49, p = 0.004); and (iii) depressive affect was associated with lower income (r = ? 0.55, p = 0.001). Findings are consistent with the adaptive boost hypothesis and add to a growing body of evidence that elevated cortisol is not universally bad. Hypothalamic–pituitary adrenal axis (HPAA) activity, such as cortisol, may be adaptive depending on a person's contextual circumstances. Based on our findings and those of previous studies, we develop a “person-in-context” model of the threat appraisal process. Integrated with life history theory, our model facilitates testable hypotheses about intra- and inter-individual variability in HPAA and adaptive consequences.     

Testosterone and androgen receptor gene polymorphism are associated with confidence and competitiveness in men

A contribution to a special issue on Hormones and Human Competition.Studies in non-human animals and humans have demonstrated the important role of testosterone in competitive interactions. Here, we investigated whether endogenous testosterone levels predict the decision to compete, in a design excluding spite as a motive underlying competitiveness. In a laboratory experiment with real monetary incentives, 181 men solved arithmetic problems, first under a noncompetitive piece rate, followed by a competition incentive scheme. We also assessed several parameters relevant to competition, such as risk taking, performance, and confidence in one's own performance. Salivary testosterone levels were measured before and 20 min after the competition task using mass spectrometry. Participants were also genotyped for the CAG repeat polymorphism of the androgen receptor gene, known to influence the efficacy of testosterone signaling in a reciprocal relationship to the number of CAG repeats. We observed a significant positive association between basal testosterone levels and the decision to compete, and that higher testosterone levels were related to greater confidence in one's own performance. Whereas the number of CAG repeats was not associated with the choice to compete, a lower number of CAG repeats was related to greater confidence in those who chose to compete, but this effect was attributable to the polymorphism's effect on actual performance. An increase in testosterone levels was observed following the experiment, and this increase varied with self-reported high-school math grades. We expand upon the latest research by documenting effects of the androgen system in confidence in one's own ability, and conclude that testosterone promotes competitiveness without spite.     

Occurrence of human-pathogenic Enterocytozoon bieneusi,Giardia duodenalis and Cryptosporidium genotypes in laboratory macaques in Guangxi,China

Captive nonhuman primates have been identified as common hosts of Enterocytozoon bieneusi, Giardia duodenalis, Cryptosporidium hominis, and Cyclospora spp., thus are potential reservoirs of some enteric parasites in humans. However, few studies have examined the source and human-infective potential of enteric parasites in laboratory nonhuman primates. In the present work, 205 fecal specimens were collected from three groups of captive Macaca fascicularis kept in different densities in a laboratory animal facility in Guangxi, China, and examined by PCR for E. bieneusi, G. duodenalis, Cryptosporidium spp., and Cyclospora spp. The infection rates of E. bieneusi and G. duodenalis were 11.3% and 1.2% in Group 1 (young animals kept individually; n = 168), 72.2% and 11.1% in Group 2 (young animals kept in groups; n = 18), and 31.6% and 5.3% in Group 3 (adults kept in groups; n = 19), respectively. Sequence analysis of PCR products showed the presence of five E. bieneusi genotypes, with genotype D (in 16/36 genotyped specimens) and a new genotype (in 15/36 genotyped specimens) as the dominant genotypes. All five E. bieneusi genotypes belonged to the zoonotic group (Group 1). The G. duodenalis genotypes (assemblages AII and B) in five specimens and C. hominis subtype (IdA14) in one specimen were also known human-pathogens, although the Cyclospora seen in one animal appeared to be unique to macaque monkeys. The higher infection rate in younger animals reared in groups and common occurrence of zoonotic genotypes indicated that human-pathogenic E. bieneusi could be transmitted efficiently in captive nonhuman primates, and group-housing was a risk factor for transmission of zoonotic pathogens in young nonhuman primates in research facilities.     

Testosterone may increase selective attention to threat in young male macaques

Animal studies indicate that sex hormones have widespread effects on the brain, cognition and emotion, but findings in humans are inconsistent. Well-controlled studies in nonhuman primates are crucial to resolve these discrepancies. In this study, we examined the effects of testosterone (T) on emotion in male rhesus monkeys. Six young adult males were tested on two emotional tasks during three hormonal conditions in a crossover design: when intact at baseline and when pharmacologically hypogonadal with add-back of T or placebo. The emotional tasks were the Approach–Avoidance task, which tested behavioral responses to three categories of objects (familiar, novel, and negative) and a Social Playback task which tested behavioral responses to scenes of unfamiliar conspecifics engaged in three types of social activities (neutral, positive, or negative). Following a 4-week baseline period, monkeys were treated with Depot Lupron, 200 μg/kg before being randomly assigned to one of two treatment groups: Depot Lupron + Testosterone Enanthate (TE, 20 mg/kg) or Depot Lupron + oil vehicle. In each treatment group, monkeys received one injection of Lupron and one injection of TE or one injection of Lupron and one injection of oil at the onset of a 4-week testing period, before crossing over to the alternate treatment for an additional 4 weeks of testing. TE treatment had no effect on behavioral measures in the Approach–Avoidance task. For the Social Playback task, however, TE significantly increased watching time of video clips which depicted fights between unfamiliar conspecifics. The enhancing effect of T on watching time for negative social scenes is consistent with human data suggesting that T decreases aversion or facilitates approach to threatening social stimuli. Further studies are needed to understand the mechanisms by which T may mediate responsiveness to social threat in male primates.     

Male mice ultrasonic vocalizations enhance female sexual approach and hypothalamic kisspeptin neuron activity

Vocal communication in animals is important for ensuring reproductive success. Male mice emit song-like “ultrasonic vocalizations (USVs)” when they encounter female mice, and females show approach to the USVs. However, it is unclear whether USVs of male mice trigger female behavioral and endocrine responses in reproduction. In this study, we first investigated the relationship between the number of deliveries in breeding pairs for 4 months and USVs syllables emitted from those paired males during 3 min of sexual encounter with unfamiliar female mice. There was a positive correlation between these two indices, which suggests that breeding pairs in which males could emit USVs more frequently had more offspring. Further, we examined the effect of USVs of male mice on female sexual behavior. Female mice showed more approach behavior towards vocalizing males than devocalized males. Finally, to determine whether USVs of male mice could activate the neural system governing reproductive function in female mice, the activation of kisspeptin neurons, key neurons to drive gonadotropin-releasing hormone neurons in the hypothalamus, was examined using dual-label immunocytochemistry with cAMP response element-binding protein phosphorylation (pCREB). In the arcuate nucleus (Arc), the number of kisspeptin neurons expressing pCREB significantly increased after exposure to USVs of male as compared with noise exposure group. In conclusion, our results suggest that USVs of male mice promote fertility in female mice by activating both their approaching behavior and central kisspeptin neurons.     

A microsphere-based duplex competitive immunoassay for the simultaneous measurements of aldosterone and testosterone in small sample volumes: Validation in human and mouse plasma

BackgroundThe small blood volumes available in rodent studies often limit adequate quantification of all hormones of interest. We report here the development of two new assays combining an extraction step with multiplex immunoassay (MIA) technology for the simultaneous determination of aldosterone and testosterone in 50 μl sample volume.MethodsFollowing solvent extraction, aldosterone and testosterone competitive immunoassays are performed incorporating biotinylated tracers and antibody-coated beads each having a unique fluorescence. Quantification is via addition of streptavidin–R–phycoerythrin (SA–PE). The assays were validated and compared to established methods. Baseline hormone levels in mice from four different strains, and changes after ACTH and HCG stimulation in CD-1 mice are shown.ResultsThe assays are sensitive (aldosterone 15 pg/ml, testosterone 12 pg/ml), reproducible (intra-/inter-assay imprecision aldosterone 5.1–15.6%/9.9–15.8% and testosterone 9.7–10.9%/7.7–11.4%) and correlate significantly to established assays (r = 0.94–0.95). Baseline aldosterone levels varied between strains, but not between the genders. Testosterone was significantly higher in male of all strains except in C57BL/6× NMRI mice. After ACTH injection, aldosterone (median, interquartile range) rose from 354 (261–396) pg/ml to 2008 (875–2467) in male and from 260 (210–576) to 1120 (734–1528) in female CD-1 mice. HCG injection in the same strain increased testosterone in male mice only (3.5 (0.4–8.3) ng/ml to 31.8 (30.4–33.9) ng/ml, P < 0.01).ConclusionsWe describe a MIA for the simultaneous measurement of aldosterone and testosterone in small volumes after extraction. In addition to presenting a new tool for steroid research in rodent models, our data show strain-dependent differences in steroid hormone metabolism in rodents.     

Intrasexual competition and body weight dimorphism in anthropoid primates

Body weight dimorphism in anthropoid primates has been thought to be a consequence of sexual selection resulting from male-male competition for access to mates. However, while monogamous anthropoids show low degrees of weight dimorphism, as predicted by the sexual selection hypothesis, polygynous anthropoids show high variation in weight dimorphism that is not associated with measures of mating system or sex ratio. This observation has led many to debate the role of other factors such as dietary constraints, predation pressure, substrate constraints, allometric effects, and phylogeny in the evolution of anthropoid weight dimorphism. Here, we re-evaluate variation in adult body weight dimorphism in anthropoids, testing the sexual selection hypothesis using categorical estimates of the degree of male-male intrasexual competition (“competition levels”). We also test the hypotheses that interspecific variation in body weight dimorphism is associated with female body weight and categorical estimates of diet, substrate use, and phylogeny. Weight dimorphism is strongly associated with competition levels, corroborating the sexual selection hypothesis. Weight dimorphism is positively correlated with increasing female body weight, but evidence suggests that the correlation reflects an interaction between overall size and behavior. Arboreal species are, on average, less dimorphic than terrestrial species, while more frugivorous species tend to be more dimorphic than folivorous or insectivorous species. Several alternative hypotheses can explain these latter results. Weight dimorphism is correlated with taxonomy, but so too are competition levels. We suggest that most taxonomic correlations of weight dimorphism represent “phylogenetic niche conservatism”; however, colobines show consistently low degrees of weight dimorphism for reasons that are not clear. Am J Phys Anthropol 103:37–68, 1997. © 1997 Wiley-Liss, Inc.     

Biological treatment of n-hexane and methanol in trickle bed air biofilters under acidic conditions

This study focuses on evaluating the degradation of n-hexane/methanol mixture in trickle-bed-air-biofilters (TBABs). Two different concentration ratios of methanol:n-hexane were evaluated (3:1) for TBAB “A” and (5:1) for TBAB “B”. Both TBABs were run and fed with nutrients buffered at pH 4 for encouraging the growth of fungi. The TBABs were loaded with pelletized diatomaceous earth support media and were run at an empty bed residence time of 120 s. n-Hexane loading rates (LRs) ranged from 0.9 to 13.2 g/m³ h for both TBABs. The corresponding methanol LRs varied from 2.3 to 37.7 g/m³ h and from 4.6 to 64.5 g/m³ h for TBABs “A” and “B”, respectively. Experimental results have shown that the degradation of n-hexane in presence of methanol is enhanced for n-hexane LRs less than 10.6 g/m³ h as compared to previous study for sole-fed n-hexane, but for n-hexane LRs of 13.2 g/m³ h, the performance of TBABs in eliminating n-hexane depended on the methanol to n-hexane ratios. The impact was less severe for TBAB “A” (RE 85%) as compared to TBAB “B” (RE 72%). This is attributed to the high LRs of methanol in TBAB “B”. n-Hexane performance stability was another advantage attained.     

The illusive search for the lowest free energy state of globular proteins and RNAs

As a consequence of the one-dimensional storage and transfer of genetic information, DNA → RNA → protein, the process by which globular proteins and RNAs achieve their three-dimensional structure involves folding of a linear chain. The folding process itself could create massive activation barriers that prevent the attainment of many stable protein and RNA structures. We consider several kinds of energy barriers inherent in folding that might serve as kinetic constraints to achieving the lowest energy state. Alternative approaches to forming 3D structure, where a substantial number of weak interactions would be created prior to the formation of all the peptide (or phosphodiester) bonds, might not be subjected to such high barriers. This could lead to unique 3D conformational states, potentially more stable than “native” proteins and RNAs, with new functionalities.     

Preliminary evidence that testosterone's association with aggression depends on self-construal

A contribution to a special issue on Hormones and Human Competition.Previous research and theory suggest testosterone is an important hormone for modulating aggression and self-regulation. We propose that self-construal, a culturally-relevant difference in how individuals define the self in relation to others, may be an important moderator of the relationship between testosterone and behaviors linked to aggression. Within two studies (Study 1 N = 80; Study 2 N = 237) and an integrated data analysis, we find evidence suggesting that acute testosterone changes in men are positively associated with aggressive behavior for those with more independent self-construals, whereas basal testosterone is negatively associated with aggression when individuals have more interdependent self-construals. Although preliminary, these findings suggest that self-construal moderates the association between testosterone and aggression, thereby paving the way toward future work examining the potential cultural moderation of the behavioral effects of testosterone.     

Improved prediction of all-cause mortality by a combination of serum total testosterone and insulin-like growth factor I in adult men

ObjectiveLower levels of anabolic hormones in older age are well documented. Several studies suggested that low insulin-like growth factor I (IGF-I) or testosterone levels were related to increased mortality. The aim of the present study was to investigate the combined influence of low IGF-I and low testosterone on all-cause mortality in men.Methods and resultsFrom two German prospective cohort studies, the DETECT study and SHIP, 3942 men were available for analyses. During 21,838 person-years of follow-up, 8.4% (n = 330) of men died. Cox model analyses with age as timescale and adjusted for potential confounders revealed that men with levels below the 10th percentile of at least one hormone [hazard ratio (HR) 1.38 (95% confidence-interval (CI) 1.06–1.78), p = 0.02] and two hormones [HR 2.88 (95% CI 1.32–6.29), p < 0.01] showed a higher risk of all-cause mortality compared to men with non-low hormones. The associations became non-significant by using the 20th percentile as cut-off showing that the specificity increased with lower cut-offs for decreased hormone levels. The inclusion of both IGF-I and total testosterone in a mortality prediction model with common risk factors resulted in a significant integrated discrimination improvement of 0.5% (95% CI 0.3–0.7%, p = 0.03).ConclusionsOur results prove that multiple anabolic deficiencies have a higher impact on mortality than a single anabolic deficiency and suggest that assessment of more than one anabolic hormone as a biomarker improve the prediction of all-cause mortality.     

Dominance, aggression and testosterone in wild chimpanzees: a test of the ‘challenge hypothesis’

The ‘challenge hypothesis’ posits that variation in male testosterone levels is more closely associated with aggression in reproductive contexts than it is with changes in reproductive physiology. Numerous bird studies support this idea, but few tests have been conducted with primates. We conducted behavioural observations and noninvasive hormone sampling of 11 male chimpanzees, Pan troglodytes schweinfurthii, in the Kanyawara study site, Kibale National Park, to test predictions of the challenge hypothesis. Results indicated that adult male chimpanzees showed significant testosterone increases during periods when parous females showed maximally tumescent sexual swellings. These periods were also marked by increased rates of male aggression. Male testosterone levels did not increase in the presence of maximally tumescent nulliparous females. Such females are less attractive to males: they are not mate-guarded, nor do rates of male aggression increase when they are swelling. Male chimpanzees copulate with parous and nulliparous females at similar rates, however, suggesting that testosterone increases in the presence of cycling parous females are associated with aggression rather than sexual behaviour. High-ranking chimpanzees were more aggressive than low-ranking males and produced higher levels of urinary testosterone. Thus, the predictions of the challenge hypothesis were generally upheld. This suggests that the hypothesis may have wider applicability among primates, including humans.     

Rapid torque development in older female fallers and nonfallers: A comparison across lower-extremity muscles

The objective of this study was to compare reaction time, joint torque, rate of torque development, and magnitude of neuromuscular activation of lower-extremity muscles in elderly female fallers and nonfallers. Participants included 11, elderly, female fallers (71.3 ± 5.4 years) and twelve nonfallers (71.3 ± 6.2 years) who completed a fall risk questionnaire. Then, maximal, voluntary, isometric contractions of the knee and ankle muscles were performed in reaction to a visual cue to determine joint torque, rate of torque development, reaction time, and nervous activation of agonists and antagonists. Results indicated that significantly more fallers reported “dizziness upon rising”, “use of balance altering medications”, “stress or depression”, “not enough sleep”, “arthritis in lower body”, “chronic pain in lower body”, and “tiring easily while walking” (all P < 0.05). Normalized dorsiflexion and plantarflexion strength scores (summation of peak torque, rate of torque development and impulse) were lower in fallers than in nonfallers (P < 0.05). When summed across lower-extremity muscle groups, fallers demonstrated 19% lower peak torque and 29% longer motor time (P < 0.05). In conclusion, comprehensive fall risk screening and prevention programs should address both neuromuscular and non-muscular factors, and, weakness of the ankle dorsiflexors and plantarflexors should be further studied as potential contributors to falls in older adults.     

In vivo skin dose measurement using MOSkin detectors in tangential breast radiotherapy

The purpose of this study is to measure patient skin dose in tangential breast radiotherapy. Treatment planning dose calculation algorithm such as Pencil Beam Convolution (PBC) and in vivo dosimetry techniques such as radiochromic film can be used to accurately monitor radiation doses at tissue depths, but they are inaccurate for skin dose measurement. A MOSFET-based (MOSkin) detector was used to measure skin dose in this study. Tangential breast radiotherapies (“bolus” and “no bolus”) were simulated on an anthropomorphic phantom and the skin doses were measured. Skin doses were also measured in 13 patients undergoing each of the techniques. In the patient study, the EBT2 measurements and PBC calculation tended to over-estimate the skin dose compared with the MOSkin detector (p < 0.05) in the “no bolus radiotherapy”. No significant differences were observed in the “bolus radiotherapy” (p > 0.05). The results from patients were similar to that of the phantom study. This shows that the EBT2 measurement and PBC calculation, while able to predict accurate doses at tissue depths, are inaccurate in predicting doses at build-up regions. The clinical application of the MOSkin detectors showed that the average total skin doses received by patients were 1662 ± 129 cGy (medial) and 1893 ± 199 cGy (lateral) during “no bolus radiotherapy”. The average total skin doses were 4030 ± 72 cGy (medial) and 4004 ± 91 cGy (lateral) for “bolus radiotherapy”. In some cases, patient skin doses were shown to exceed the dose toxicity level for skin erythema. Hence, a suitable device for in vivo dosimetry is necessary to accurately determine skin dose.