Morgan Smith

All Publications

• Fecal Microbiota and Associated Metabolites Are Minimally Affected by Ten Weeks of Resistance Training in Younger and Older Adults. Sports (Basel, Switzerland) Agyin-Birikorang, A., Lennon, S., Smith, K. S., Van Der Pol, W., Smith, M. A., Sexton, C. L., Lamb, D. A., Young, K. C., Mobley, C. B., Huggins, K. W., Roberts, M. D., Frugé, A. D. 2025; 13 (4)

  Abstract

  Preclinical evidence suggests that short chain fatty acids (SCFAs) produced by gut microbiota may impact body composition and muscle growth. While aging is implicated in negative alterations to the gut microbiome, exercise may mitigate these changes. Limited human evidence indicates that resistance training (RT) does not appreciably alter the gut microbiome in older adults, and no human study has examined whether resistance training differentially alters the gut microbiome and associated SCFAs between younger and older individuals. Therefore, we examined whether 10 weeks of RT differentially altered fecal microbiota composition, fecal and circulating SCFAs, and serum markers associated with gastrointestinal integrity in two cohorts of adults. Fecal and serum samples were obtained from untrained younger (22 ± 2 years, n = 12) and older (58 ± 8 years, n = 12) participants prior to and following 10 weeks of supervised twice-weekly full-body RT. Outcome measures immediately before (PRE) and after the intervention (POST) included dual X-ray absorptiometry for body composition, ultrasound for vastus lateralis (VL) thickness, 16S rRNA gene sequencing fecal microbiome data, serum and fecal SCFAs measured by gas chromatography, and serum intestinal fatty acid-binding protein 2 (FABP2), lipopolysaccharide-binding protein (LBP), and leucine-rich alpha-2 glycoprotein (LRG-1) quantified by enzyme-linked immunosorbent assays. Main effects and interactions were measured by repeated measures analysis of variance (group × time; G × T) for all dependent variables, and Spearman correlations were used to explore relationships among changes in relevant outcomes. The intervention significantly increased VL thickness and lean body mass (p < 0.05) equally in both groups. Although group differences in microbiome beta diversity were identified, no effects of age, time, or their interaction were observed for the alpha diversity measures. Seven SCFAs were detected in the fecal samples, albeit no significant age, time, or interaction effects were evident. In serum, acetic acid was the only SCFA detected, with no significant age, time, or interaction effects. Serum LRG1 decreased for all participants (p = 0.007) with higher levels in younger adults (p = 0.015), but no G × T interactions were observed for this marker, serum FABP2, or LBP. No significant correlations were observed among RT-induced changes in muscle mass-related outcomes and changes in fecal microbiome diversity, total or individual SCFAs, or serum FABP2/LBP/LRG-1. These results highlight that 10 weeks of RT largely does not affect fecal microbiota, associated SCFAs, or select markers of gastrointestinal integrity in untrained younger or older adults.

  View details for DOI 10.3390/sports13040098

  View details for PubMedID 40278724

• How the Menstrual Cycle Can Be Utilized During Sports Training, Performance, and Recovery through Wearable Technology: A Narrative Review for Researchers, Physicians, Coaches, and Athletes. Seminars in reproductive medicine Hunter, N. N., Smith, M. A. 2024

  Abstract

  The menstrual cycle (MC) serves as a vital indicator of overall health and metabolic function, regulated by the hypothalamic-pituitary axis and involving a complex interplay of hormones. Understanding these hormonal dynamics is crucial for deciphering an individual's physiological status and performance potential, particularly in athletes. Studies regarding the MC's impact on athletic performance and training often lack inclusivity, standardized methodologies, and inconsistent biological definitions, hindering comprehensive conclusions. Moreover, societal inequalities contribute to the underrepresentation of female athletes in research, exacerbating the lack of understanding regarding female physiology in sports medicine. Leveraging wearable technology presents a promising avenue for both tracking MCs and optimizing athletic training/recovery. Wearables offer real-time monitoring of biometrics that often correlate with hormonal fluctuations, and lifestyle trends (diet, sleep, stress) aiding in personalized training schedules and performance optimization. Integrating data collected by MC dynamics and wearable technology into athletic training has the potential to decrease the generally perceived negative impacts MC has on athletic performance. Addressing gaps in research methodologies and promoting awareness among athletes, coaches, and healthcare professionals are essential steps toward maximizing the potential of MC-informed training strategies.

  View details for DOI 10.1055/s-0044-1791508

  View details for PubMedID 39424358

• The effects of resistance training to near volitional failure on motor unit recruitment during neuromuscular fatigue PEERJ Beausejour, J. P., Knowles, K. S., Pagan, J. I., Rodriguez, J. P., Sheldon, D., Ruple, B. A., Plotkin, D. L., Smith, M. A., Godwin, J. S., Sexton, C. L., McIntosh, M. C., Kontos, N. J., Libardi, C. A., Young, K., Roberts, M. D., Stock, M. S. 2024; 12: e18163

  Abstract

  It is unclear whether chronically training close to volitional failure influences motor unit recruitment strategies during fatigue.We compared resistance training to near volitional failure vs. non-failure on individual motor unit action potential amplitude (MUAP) and surface electromyographic excitation (sEMG) during fatiguing contractions.Nineteen resistance-trained adults (11 males, 8 females) underwent 5 weeks (3×/week) of either low repetitions-in-reserve (RIR; 0-1 RIR) or high RIR training (4-6 RIR). Before and after the intervention, participants performed isometric contractions of the knee extensors at 30% of maximal peak torque until exhaustion while vastus lateralis sEMG signals were recorded and later decomposed. MUAP and sEMG excitation for the vastus lateralis were quantified at the beginning, middle, and end of the fatigue assessment.Both training groups improved time-to-task failure (mean change = 43.3 s, 24.0%), with no significant differences between low and high RIR training groups (low RIR = 28.7%, high RIR = 19.4%). Our fatigue assessment revealed reduced isometric torque steadiness and increased MUAP amplitude and sEMG excitation during the fatiguing task, but these changes were consistent between groups.Both low and high RIR training improved time-to-task failure, but resulted in comparable motor unit recruitment during fatiguing contractions. Our findings indicate that both low and high RIR training can be used to enhance fatiguability among previously resistance-trained adults.

  View details for DOI 10.7717/peerj.18163

  View details for Web of Science ID 001339225400004

  View details for PubMedID 39421412

  View details for PubMedCentralID PMC11485100

• Bone Characteristics Among Female Endurance Athletes At Risk For Relative Energy Deficiency In Sport Flora, J. L., Smith, M., Roberts, A., Kent, K., Long, J., Zhong, Y., Roche, M., Snyder, M., Kraus, E. LIPPINCOTT WILLIAMS & WILKINS. 2024: 58-59

  View details for Web of Science ID 001315123200129

• Resistance training in humans and mechanical overload in rodents do not elevate muscle protein lactylation. Frontiers in physiology Mattingly, M. L., Ruple, B. A., Sexton, C. L., Godwin, J. S., McIntosh, M. C., Smith, M. A., Plotkin, D. L., Michel, J. M., Anglin, D. A., Kontos, N. J., Fei, S., Phillips, S. M., Mobley, C. B., Vechetti, I., Vann, C. G., Roberts, M. D. 2023; 14: 1281702

  Abstract

  Although several reports have hypothesized that exercise may increase skeletal muscle protein lactylation, empirical evidence in humans is lacking. Thus, we adopted a multi-faceted approach to examine if acute and subchronic resistance training (RT) altered skeletal muscle protein lactylation levels. In mice, we also sought to examine if surgical ablation-induced plantaris hypertrophy coincided with increases in muscle protein lactylation. To examine acute responses, participants' blood lactate concentrations were assessed before, during, and after eight sets of an exhaustive lower body RT bout (n = 10 trained college-aged men). Vastus lateralis biopsies were also taken before, 3-h post, and 6-h post-exercise to assess muscle protein lactylation. To identify training responses, another cohort of trained college-aged men (n = 14) partook in 6weeks of lower-body RT (3x/week) and biopsies were obtained before and following the intervention. Five-month-old C57BL/6 mice were subjected to 10 days of plantaris overload (OV, n = 8) or served as age-matched sham surgery controls (Sham, n = 8). Although acute resistance training significantly increased blood lactate responses 7.2-fold (p < 0.001), cytoplasmic and nuclear protein lactylation levels were not significantly altered at the post-exercise time points, and no putative lactylation-dependent mRNA was altered following exercise. Six weeks of RT did not alter cytoplasmic protein lactylation (p = 0.800) despite significantly increasing VL muscle size (+3.5%, p = 0.037), and again, no putative lactylation-dependent mRNA was significantly affected by training. Plantaris muscles were larger in OV versus Sham mice (+43.7%, p < 0.001). However, cytoplasmic protein lactylation was similar between groups (p = 0.369), and nuclear protein lactylation was significantly lower in OV versus Sham mice (p < 0.001). The current null findings, along with other recent null findings in the literature, challenge the thesis that lactate has an appreciable role in promoting skeletal muscle hypertrophy.

  View details for DOI 10.3389/fphys.2023.1281702

  View details for PubMedID 37841321