Bacteria residing in the human gastrointestinal tract has a symbiotic relationship with its host. Animal models have demonstrated a relationship between exercise and gut microbiota composition. This was the first study to explore the relationship between cardiorespiratory fitness (maximal oxygen consumption, VOmax) and relative gut microbiota composition (Firmicutes to Bacteroidetes ratio [F/B]) in healthy young adults in a free-living environment. Twenty males and 17 females (25.7 ± 2.2 years), who did not take antibiotics in the last 6 months, volunteered for this study. VOmax was measured using a symptom-limited graded treadmill test. Relative microbiota composition was determined by analyzing DNA extracted from stool samples using a quantitative polymerase chain reaction that specifically measured the quantity of a target gene (16S rRNA) found in Firmicutes and Bacteroidetes. Relationships between F/B and potentially related dietary, anthropometric, and fitness variables were assessed using correlation analyses with an appropriate Bonferroni adjustment (p < .004). The average F/B ratio in all participants was 0.94 ± 0.03. The F/B ratio was significantly correlated to VOmax (r = .48, p < .003), but no other fitness, nutritional intake, or anthropometric variables (p > .004). VOmax explained ∼22% of the variance of an individual's relative gut bacteria as determined by the F/B ratio. These data support animal findings, demonstrating a relationship between relative human gut microbiota composition and cardiorespiratory fitness in healthy young adults. Gastrointestinal bacteria is integral in regulating a myriad of physiological processes, and greater insight regarding ramifications of exercise and nutrition on gut microbial composition may help guide therapies to promote human health.

In 2007 the National Institutes of Health launched the Human Microbiome Project (HMP), an interdisciplinary research initiative seeking to characterize the contribution of human gut microbiota to health and disease (Turnbaugh et al., 2007). Subsequent findings have demonstrated compelling relationships between human gut microbiome composition and many leading causes of death worldwide including cardiovascular disease (Wang et al., 2011), diabetes (Larsen et al., 2010), and cancer (Ahn et al., 2013). Although the gut microbiome is suggested to exhibit exceptional plasticity (Gomez et al., 2019), a detailed understanding of the factors determining human microbiome assembly is lacking (Relman, 2015).

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Metabolic carts use indirect calorimetry to measure energy expenditure (EE). Because these systems are large, portable wearable metabolic devices (PWMD) have been developed to measure EE outside of the laboratory. The purpose of this review article is to provide an overview of the current state of knowledge regarding the 1) application and 2) efficacy of portable metabolic devices. This literature review covered the applications and efficacy of PWMD during exercise. Studies that investigated the efficacy of PWMD evaluated the volume of oxygen consumption (VO 2 ) and carbon dioxide production (VCO 2 ) measurements compared to criterion devices. Thirty-four articles studied the application and efficacy of PWMD during walking, running, cycling, rowing, badminton, and tennis. Eight walking and running studies reported that PWMD overestimated VO 2 (0.30-0.63 L/min; ~5.2-22.2% difference) and VCO 2 (0.42-0.62 L/min; 3% difference) compared to criterion devices. Nine cycling studies showed similar trends for VO 2 (0.1-0.3 L/min; ~4.4-13.0% difference) and VCO 2 (0.14-0.30 L/min; 6.9% difference). Generally, as exercise intensity increased, variability between devices correspondingly increased. However, six studies reported no significant differences between PWMD and criterion devices (ICC: 0.93-0.97; r = 0.91-.99). Regarding reliability, five studies reported that popular PWMD had high test-retest reliability for VO 2 (ICC: 0.87-0.99) and VCO 2 (ICC: 0.72-0.81) while walking/running at different speeds/gradients. Conversely, one study reported low test-retest reliability while running at high speeds for short distances. As technology emerges, PWMD are becoming widely used in clinical, fitness, and research. While data on their validity remains ambiguous, their test-retest reliability may be a more important factor to consider when using a PWMD.

INTRODUCTION: Active virtual reality gaming (AVRG) provides an alternative option to traditional exercise modalities. Recent studies have shown that exercising using AVRG can lead to exercise intensities that meet guidelines for health benefits. Tracking caloric energy expenditure (EE) during exercise has shown to be effective for improving body composition and health, but no study to date has investigated differences between the accuracy of EE estimations from various devices during AVRG. OBJECTIVE: The purpose of this study was to compare two methods of tracking EE (movement displacement and heart rate) versus the laboratory "gold standard" (indirect calorimetry) during AVRG. METHODS: Eleven participants (6 females, 5 males, 22.5 ± 2.5 y) played 15-min of AVRG, while undergoing three different methods of EE tracking simultaneously: indirect calorimetry measuring oxygen consumption (VO 2 ), movement displacement data from the VR system (MOV), and a heart rate monitor (HR). RESULTS: Total estimated EE during the 15-min gameplay was 69.21 ± 10.85, 77.42 ± 24.63, and 134.00 ± 32.98 kcals for VO 2 , MOV, and HR, respectively. The HR measure over-estimated kcals (p < 0.0001) compared to VO 2 , but there was no significant difference between VO 2 and MOV EE estimates. CONCLUSION: These results suggest 1) movement displacement may be an accurate method to track EE while playing VR games compared to indirect calorimetry, and 2) new equations must be developed specifically for AVRG to improve HR estimates of EE during gameplay.

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