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Evaluating the Clinical Utility of Daily Heart Rate Variability Assessment for Classifying Meaningful Change in Testosterone-to-Cortisol Ratio: A Preliminary Study.
DeBlauw, JA, Crawford, DA, Kurtz, BK, Drake, NB, Heinrich, KM
International journal of exercise science. 2021;14(3):260-273
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Exercise-induced hormonal responses are controlled by the hypothalamic-pituitary adrenal axis, a key regulator of homeostasis, which responds to stress by triggering a series of endocrine changes resulting in the release of testosterone (T) and cortisol (C). The aim of this study was to determine the relationship between daily resting heart rate variability (HRV) and pre-exercise T:C ratio and evaluate the clinical utility (i.e., diagnostic validity and reliability) of daily HRV assessment in classifying atypical T:C ratio changes throughout a nine-week high-intensity functional training (HIFT) intervention. This study is a secondary analysis of a subset of participants from a larger study. Eight recreationally active men and women ages 18-35 were recruited for participation. Following 14 days of baseline HRV assessments, participants were randomized to either the treatment or control condition. Results show a statistically significant negative relationship between HRVdaily and the T:C ratio throughout 9-weeks of HIFT. Additionally, there was no significant relationship found between C and HRVdaily and neither sex nor group were significant factors. Authors conclude that their findings emphasize the potential of HRV for the guidance of training, however, as hormonal responses to training are highly individual, the creation of individual autonomic nervous systems and hormonal profiles would increase the accuracy of training stress modulation.
Abstract
The study purpose was to determine the relationship of resting heart rate variability (HRV) and testosterone to cortisol (T:C) ratio, along with the diagnostic ability of HRV to assess changes in T:C ratio during a 9-week high-intensity functional training intervention. Eight recreationally-active men (n = 4, age 24.25 ± 1.75 yrs, height 181.25 ± 3.86 cm, weight 79.68 ± 11.66 kg) and women (n = 4, age 26 ± 3.6 yrs, height 164.25 ± 3.3, weight 73.4 ± 8.42) completed daily HRV measurements (HRVdaily) using photoplethysmography via a commercially-available smartphone application along with weekly saliva samples. Saliva samples were analyzed for concentrations of testosterone (T) and cortisol (C) via enzyme-linked immunosorbent assays. Upon study completion 72 data points were available, due to participant compliance and inadequate saliva sample, 67 matched pairs of HRV and T:C ratio were analyzed. A statistically significant negative relationship (n = 67, r = -.315, p < 0.05) was found between HRVdaily and saliva T:C ratio concentrations within aggregate data. Individual participant relationships showed considerable variability (r = -0.101 - 0.665, p = 0.103 to 0.829 The model which best explained the data resulted in AIC = 130.247 with factors HRVdaily (β = -0.218, 95%CI = -0.391, -0.044, t = -2.46, p < 0.05), Sex (β = 0.450, 95%CI = -0.214, 1.114, t = 1.113, p = 0.242), and Group (β = -0.394, 95%CI = -1.089, 0.302, t = -1.11, p = 0.311). Diagnostically, HRVdaily demonstrates excellent sensitivity (95%), but poor specificity (5%) for detecting meaningful changes in T:C ratio. Assessment of HRVdaily may be a clinically valid proxy measure for monitoring hormonal changes throughout a training intervention.
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The effects of d-aspartic acid supplementation in resistance-trained men over a three month training period: A randomised controlled trial.
Melville, GW, Siegler, JC, Marshall, PWM
PloS one. 2017;12(8):e0182630
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D-aspartic acid (DAA) is an amino acid that is currently purported as a testosterone-boosting supplement. Research has shown that DAA supplementation increases testosterone levels in untrained men, however in trained men has been shown to produce no effect. The aim of this study was to evaluate the effects of DAA to alter testosterone levels over three months of resistance training in 22 men. Participants were randomised to receive DAA or placebo and performed 12 weeks of supervised resistance training. Blood analyses and muscle measurements were assessed at baseline, six weeks and 12 weeks. This study found that DAA supplementation is ineffective in trained men at changing testosterone levels or positively affecting training outcomes. According to these findings, the authors suggest future studies further exploring the effects of supplementation in a trained population.
Abstract
CONTEXT Research on d-aspartic acid (DAA) has demonstrated increases in total testosterone levels in untrained men, however research in resistance-trained men demonstrated no changes, and reductions in testosterone levels. The long-term consequences of DAA in a resistance trained population are currently unknown. OBJECTIVE To evaluate the effectiveness of DAA to alter basal testosterone levels over 3 months of resistance training in resistance-trained men. DESIGN Randomised, double-blind, placebo controlled trial in healthy resistance-trained men, aged 18-36, had been performing regular resistance training exercise for at least 3 d.w-1 for the previous 2 years. Randomised participants were 22 men (d-aspartic acid n = 11; placebo n = 11) (age, 23.8±4.9 y, training age, 3.2±1.5 y). INTERVENTION D-aspartic acid (6 g.d-1, DAA) versus equal-weight, visually-matched placebo (PLA). All participants performed 12 weeks of supervised, periodised resistance training (4 d.w-1), with a program focusing on all muscle groups. MEASURES Basal hormones, total testosterone (TT), free testosterone (FT), estradiol (E2), sex-hormone-binding globulin (SHBG) and albumin (ALB); isometric strength; calf muscle cross-sectional area (CSA); calf muscle thickness; quadriceps muscle CSA; quadriceps muscle thickness; evoked V-wave and H-reflexes, were assessed at weeks zero (T1), after six weeks (T2) and after 12 weeks (T3). RESULTS No change in basal TT or FT were observed after the intervention. DAA supplementation (n = 10) led to a 16%, 95% CI [-27%, -5%] reduction in E2 from T1-T3 (p<0.01). The placebo group (n = 9) demonstrated improvements in spinal responsiveness (gastrocnemius) at the level of the alpha motoneuron. Both groups exhibited increases in isometric strength of the plantar flexors by 17%, 95% CI [7%, 28%] (p<0.05) as well as similar increases in hypertrophy in the quadriceps and calf muscles. CONCLUSIONS The results of this paper indicate that DAA supplementation is ineffective at changing testosterone levels, or positively affecting training outcomes. Reductions in estradiol and the blunting of peripheral excitability appear unrelated to improvements from resistance training. TRIAL REGISTRATION Australian New Zealand Clinical Trials Registry ACTRN12617000041358.