Biology subjects

Stock, M. S.

Publications and source records attributed to Stock, M. S..

4 recordsLinked to original sources

bioRxiv2024

Leg immobilization and subsequent recovery resistance training affect skeletal muscle angiogenesis related markers in young healthy adults regardless of prior resistance training experience

We recently reported that resistance trained (T, n=10) and untrained (UT, n=11) young adults experience vastus lateralis (VL) muscle atrophy following two weeks of disuse, and 8 weeks of recovery resistance training (RT) promotes VL hypertrophy in both participant cohorts. However, angiogenesis targets and muscle capillary number were not examined and currently no human studies that have sought to determine if disuse followed by recovery RT affects these outcomes. Thus, we examined whether disuse and/or recovery RT affected these outcomes. All participants underwent two weeks of left leg immobilization using locking leg braces and crutches followed by eight weeks (3d/week) of knee extensor focused progressive RT. VL biopsies were obtained at baseline (PRE), immediately after disuse (MID), and after RT (POST). Western blotting was used to assay angiogenesis markers and immunohistochemistry was performed in 16/21 participants to determine type I and II muscle fiber capillary number. Significant main effects of time (p<0.05) were observed for protein levels of VEGF (MID 0.100). Although disuse and recovery RT affect skeletal muscle angiogenesis-related protein targets, prior training history does not differentially affect these outcomes. NEW AND NOTEWORTHYThis is the first study to examine how limb immobilization and recovery resistance training affect molecular outcomes related to angiogenesis in younger adults with or without a prior training history. Regardless of resistance training history, the molecular responses are largely similar between participant cohorts and is suggestive of a reduced (pre-mid) and increased (mid-post) angiogenic response, with disuse and subsequent recovery resistance training.

physiology↗

bioRxiv2024

CHANGES IN MUSCLE QUALITY FOLLOWING SHORT-TERM RESISTANCE TRAINING IN OLDER ADULTS: A COMPARISON OF ECHO INTENSITY AND TEXTURE ANALYSIS

BackgroundSkeletal muscle echo intensity (EI) is associated with functional outcomes in older adults, but resistance training interventions have shown mixed results. Texture analysis has been proposed as a novel approach for assessing muscle quality, as it captures spatial relationships between pixels. PurposeTo examine changes in first-order (EI) and second-order (texture) features of muscle quality following lower-body resistance training in older adults. MethodsTwelve older adults (2 males, 10 females; mean {+/-} SD age = 70 {+/-} 5 years) completed 6 weeks of progressive resistance training, consisting of twice-weekly sessions at 85% of estimated 1RM. Pre- and post-intervention assessments included ultrasound imaging of the rectus femoris (RF) and vastus lateralis (VL), 5-repetition maximum (5RM) leg extension strength, and maximal voluntary isometric contraction (MVIC) force. Ultrasound images were analyzed for EI and texture features using gray-level co-occurrence matrix (GLCM) analysis. ResultsLarge improvements were observed in 5RM leg extension strength (p < 0.001, d = 2.09), MVIC force (p = 0.006, d = 0.969), and RF EI (uncorrected: p = 0.003, d = 0.727; corrected: p = 0.012, d = 0.864). No significant changes were observed in muscle size, VL EI, or texture features for either muscle. ConclusionsShort-term resistance training improved strength and RF muscle quality as measured by EI. However, texture analysis features were not sensitive to changes following training. These findings suggest that traditional EI measures may be more appropriate than texture analysis for tracking changes in muscle quality following resistance training in older adults. NEW & NOTEWORTHYWe studied muscle quality changes after 6 weeks of resistance training in older adults, comparing traditional EI to texture analysis. Despite significant strength gains, only RF EI improved, with minimal changes in muscle size, VL EI, or texture parameters. Surprisingly, texture analysis was less sensitive than traditional EI in detecting muscle quality changes. Our results suggest that conventional EI measures may be more suitable for evaluating short-term adaptations to resistance training in older adults.

physiology↗

bioRxiv2024

Effects of leg immobilization and recovery resistance training on skeletal muscle-molecular markers in previously resistance trained versus untrained adults

We sought to examine how resistance training (RT) status in young healthy individuals, either well-trained (T, n=10 (8 males)) or untrained (UT, n=11 (8 males)), affected muscle size and molecular markers with leg immobilization followed by recovery RT. All participants underwent two weeks of left leg immobilization via the use of crutches and a locking leg brace. After this two-week period, all participants underwent eight weeks (3 d/week) of knee extensor focused progressive RT. Vastus lateralis (VL) ultrasound-derived thickness and muscle cross-sectional area were measured at baseline (PRE), immediately after disuse (MID), and after RT (POST) with VL muscle biopsies collected at these time points. T and UT presented lower ultrasound derived VL size (cross-sectional area and thickness) values at MID versus PRE (p[≤]0.001), and values increased in both groups from MID to POST (p<0.05); however, VL size increased from PRE to POST in UT only (p<0.001). Mean and type II myofiber cross-sectional area (fCSA) values demonstrated a main effect of time where PRE and POST were greater than MID (p<0.05) and main effect of training status where T was greater than UT (P[≤]0.012). In both groups, satellite cell number was not affected by leg immobilization but increased in response to RT (p[≤]0.014), with T being greater than UT across all time points (p=0.004). Additionally, ribosome content (total RNA) decreased (p=0.010) from PRE to MID while the endoplasmic reticulum stress proteins (BiP, Xbp1s, and CHOP) increased from MID to POST regardless of training status. Finally, the phosphorylation states of mechanistic target of rapamycin complex-1 signaling proteins were not significantly altered for either group throughout the intervention. In conclusion, immobilization-induced muscle atrophy and recovery RT hypertrophy outcomes are similar between UT and T participants, and the lack of molecular signature differences between groups supports these findings. However, these data are limited to younger adults undergoing non-complicated disuse. Thus, further investigation to determine the impact of training status on prolonged leg immobilization models mirroring current medical protocols (e.g., following orthopedic injury and surgery) is warranted.

physiology↗

bioRxiv2024

A Comparison of Techniques to Determine Active Motor Threshold for Quadriceps Transcranial Magnetic Stimulation Research

The determination of active motor threshold (AMT) is a critical step in transcranial magnetic stimulation (TMS) research protocols involving voluntary muscle contractions. As AMT is frequently determined using an absolute electromyographic (EMG) threshold (e.g., 200{micro}V peak-to-peak amplitude), wide variation in EMG recordings across participants has given reason to consider a relative threshold (e.g., = 2x background EMG) for AMT determination. However, these approaches have not been systemically compared. PURPOSE: We sought to compare the AMT estimations derived from absolute and relative criteria commonly used to determine AMT in the quadriceps muscles, and assess the test-retest reliability of each approach (absolute = 200{micro}V vs. relative = 2x background EMG). METHODS: Eighteen young adults (9 males and 9 females; mean {+/-} SD age = 23 {+/-} 2 years) visited the research laboratory on two occasions. All testing was conducted on the dominant limb. During each laboratory visit, maximal voluntary isometric contraction (MVIC) quadriceps torque was measured, with all subsequent TMS procedures conducted as participants maintained 10% of MVIC torque. AMT was derived from each criterion using motor evoked potentials recorded from the vastus lateralis (VL) and defined as the lowest stimulator output (SO%) needed to meet the specified criteria within [≥] 5/10 pulses. The order of criteria (i.e., absolute vs. relative) was randomized during the first laboratory visit, and counterbalanced during the second visit. A paired samples t-test, 95% confidence intervals and the effect size were used to compare mean differences in AMT estimations obtained from each criterion during the second laboratory visit. Paired samples t-tests, intraclass correlation coefficients (ICC2,1), standard errors of measurement (SEMs), and the minimal difference (MD) scores were calculated to assess test-retest reliability of each AMT criterion. RESULTS: Differences between the AMT criteria were small and not statistically significant (absolute criterion mean = 48.9%, relative criterion mean = 47.4%; p = .309, Cohens d = 0.247). The absolute criterion demonstrated moderate to excellent reliability (ICC2,1= .866 [0.648 - 0.950], SEM = 7.9%, MD = 10.4%), but higher AMTs were observed in the second visit compared to the first (p = 0.043). The relative criteria demonstrated good-to-excellent test-retest reliability (ICC2,1= .894 [0.746 - 0.959], SEM = 6.9%, MD = 8.9%) and AMTs were not different between visits (p = 0.420). CONCLUSIONQuantifying AMT with an absolute voltage threshold of 200{micro}V peak-to-peak amplitude and a relative voltage threshold 2x background EMG resulted in similar estimations within a single testing session. However, the relative voltage criterion demonstrated superior test-retest reliability. TMS researchers aiming to track corticospinal characteristics across visits should consider implementing relative criterion approaches during their AMT determination protocol.

neuroscience↗