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Biomechanics/Neuromuscular

(3) YOGA ALTERS KNEE EXTENSOR MAXIMAL STRENGTH AND MOTOR UNIT FIRING BEHAVIOR OF THE VASTUS LATERALIS IN HEALTHY ADULTS

Thursday, July 13, 2023
9:00 AM – 9:15 AM East Coast USA Time
Location: Milano I-II
Abstract Details: Much yoga research is focused on specific populations such as sedentary, diseased, and older adults, often neglecting a healthy population that could also participate in the practice. Motor unit (MU) control properties are commonly studied with resistance- and endurance-training interventions. Although various health benefits have been associated with yoga, no study has examined the effects of a yoga intervention on single MU behavior.

Purpose: The purpose of this study was to examine the effects of an 8-week yoga intervention on maximal strength of the knee extensors and MU behavior of the vastus lateralis (VL) in a healthy, recreationally active population.

Methods: Eight healthy, adult males and females (X̅±SD; age=23.4±4.9yrs, hheight=175.1±6.1cm, body mass=79.9±12.8kg) participated in 8 weeks of hatha vinyasa yoga twice per week (16, 1-hour sessions). Subjects reported various physical activity histories prior to the study. Before (PRE) and after (POST) 8 weeks of yoga, subjects performed 3 isometric voluntary contractions (MVCs) of the knee extensors, followed by an isometric trapezoidal muscle action at 50% MVC. The highest torque output from each visit determined maximal strength and the torque level for the subsequent 50% MVC. Electromyographic (EMG) signals were recorded from the VL and decomposed to extract action potentials and firing rates of single MUs for the submaximal muscle actions. The recruitment thresholds (RTs) (%MVC), MU action potential amplitudes (MUAPAMPS) (mV), and mean firing rates (MFRs) (pulses per second [pps]) at the targeted torque were calculated for each MU. MUs with accuracies >90% were used for analyses. Simple linear regression models were performed to calculate the slopes and y-intercepts for the MUAPAMP and MFR vs. RT relationships. EMG amplitude (EMGRMS) at steady torque for the 50% MVC was normalized (N-EMGRMS) (%) to MVC EMGRMS. Six separate paired samples t-tests were performed comparing MVC, N-EMGRMS, and the slopes and y-intercepts for the MUAPAMP and MFR vs. RT relationships at PRE and POST. Alpha was set at 0.05.

Results: There were significant increases for MVC (PRE = 239.6 ± 113.3 Nm, POST = 267.5 ± 126.4 Nm; p = 0.044) and the y-intercepts for the MFR vs. RT relationships (PRE = 25.2 ± 5.2 pps, POST = 28.1 ± 6.6; p = 0.047). However, there were no changes for N-EMGRMS (p = 0.855), the slopes for the MFR vs. RT relationships (p = 0.065), nor the slopes (p = 0.887) and y-intercepts (p = 0.456) for the MUAPAMP vs. RT relationships.

Conclusions: Knee extensor strength improved following 8 weeks of yoga in a healthy, recreationally active population. The greater y-intercepts for the MFR vs. RT relationships without changes in N-EMGRMS at POST suggests increased excitability for the overall MU pool, and may help explain the increase in maximal strength. Additionally, the similar MUAPAMPS vs. RT relationships coefficients at PRE and POST further suggests the increase in firing rate behavior is due to alterations in intrinsic MU properties, and not a change in MU recruitment patterns or MU size. PRACTICAL APPLICATION: Yoga can be implemented into active lifestyles and elicit positive performance adaptations. Consistent yoga practice has the potential to increase MU excitability and increase maximal strength of the leg extensors. Future research should investigate the effects of hatha vinyasa yoga on maximal strength and MU behavior of upper body muscles.

Acknowledgements: none