LAUSR

Yoga is an umbrella term that refers to a series of activities including different holistic exercises (e.g., balance, stretching, breathing exercises) and diverse styles of practice (Cramer et al., 2016). Regarding styles, yoga can vary from a more physical practice, such as ashtanga yoga, to a more meditation-based practice, such as Yoga Nidra (YN; literally yoga sleep). YN was developed in 1976 as a relatively easy-to-learn meditation practice to be used by various people regardless of their previous experience (Moszeik et al., 2020). Unlike other meditation-based practices (e.g., transcendental meditation, body scan), considered as aware awake states, YN is rather considered as an aware sleep state (Sharpe et al., 2021). More precisely, this practice, executed in supine position, naturally stimulates a hypnagogic state wherein an individual is physiologically asleep yet maintains an internal/external awareness (Sharpe et al., 2021); there is a withdraw from other senses, and only the auditory channel is open so that the participant stays aware of the directions coming from the instructor, but practices detachment from all other stimuli. YN interventions have been associated with significant improvements in sleep parameters such as sleep onset latency and sleep quality (Datta et al., 2017; Moszeik et al., 2020) because of a general parasympathetic dominance (Markil et al., 2012) and a subsequent high cardiac vagal control (Werner et al., 2015; see also YN Effects and Potential Benefits on Athletes); it first stimulates the parasympathetic nervous system increasing heart rate variability (HRV), or its high-frequency components (Markil et al., 2012), and alpha waves, to then demonstrate the symptoms of deep, non-REM sleep, including theta and delta brain waves (Parker et al., 2013). One of the core components of YN sessions is represented by a personal resolution called Sankalpa, the Sanskrit word for “intention.” This resolution is expressed as a simple, short, and positive sentence (e.g., “I am calm,” “I am successful”), which is repeated in the beginning and in the end of the session. Its regular mental repetition “drives” the unconscious toward the desired state by stimulating cognitive restructuring processes (Moszeik et al., 2020). Encompassing a sequence of guided body awareness, visualization, and breathing exercises, YN is also described as a complete and systematic method of inducing physical and mental relaxation achieved by turning inward, away from most of outer experiences (Saraswati, 2009; Parker et al., 2013). For a more comprehensive description of YN stages, see Table 1.