Resonance frequency breathing (RFB) is a widely used self-paced breathing paradigm that seeks to enhance cardiorespiratory control (Lehrer & Gevirtz 2014) and in turn promote optimal physiological and emotional regulation (Lehrer et al., 2020). During RFB, individuals maintain a steady breathing rate at 6 breaths per minute (BPM) with the aid of a pacing stimulus (e.g., a computerised visual or auditory cue). Specifically, RFB works by increasing the pattern of synchronicity between heart rate and respiration. Previous studies indicate that biofeedback based RFB, for example, feedback on heart rate variability (HRV) which has been shown to increase with RFB, is associated with improved performance on tasks assessing executive function (EF), such as working memory and attention (for a systematic review, see Tinello et al., 2021). Whilst more recent research suggests a positive correlation between this type of intervention and EF performance, less is known about the extent to which online delivered RFB improves EF (Laborde et al., 2021, 2022; Bonomini et al., 2020; Chaitanya et al., 2022). Such research is necessary to establish the versatility and (far) transfer effects of RFB beyond the laboratory setting. If robust significant effects are observed, this would support the development of accessible and scalable online interventions aimed at emotionally vulnerable individuals (e.g., high worriers). Whilst impaired EF has long been associated with the maintenance of clinical anxiety and pathological worry (Eysenck et al., 2011; Fox et al., 2015), the efficacy of traditional cognitive training concerning negative emotional symptoms remains disputed (Keshavan et al., 2014). In a recent study, Hotton, Derakshan & Fox (2018) found that both active N-back training (reaching up to four N-back levels) and active N-back control training (remaining at the level of one-back only) provide equal improvement in working memory capacity and worry, although training-related improvements during active N-back training was positively associated with working memory enhancement and worry reduction. Such findings illustrate that there is a need for research to identify factors that augment existing EF remedial approaches (e.g., methods for optimising far-transference effects, individual differences etc), that in turn provide a stronger clinical impact for reducing anxiety and worry. If successful then, online RFB may provide a promising target for EF enhancement and as suggested by the previous literature provide an effective strategy for emotional regulation (Lehrer et al., 2020). The current study brings this objective into focus by examining the relationship between acute online implemented RFB and EF, assessed by the N-back task. The single N-back task is selected as the key outcome measure of EF, based on the previous literature utilizing this task in worry-based samples, in addition to recommendations for implementing single N-back as a simpler training paradigm, given that single- and dual- N-back versions provide equal training effects (Jaeggi et al., 2010). In accordance with neurovisceral integration theory (Thayer et al., 2009) and the resonance breathing model (Lehrer & Gevirtz, 2013), the current study predicts that EF performance is greater following RFB (6BPM) as compared to an active control breathing condition (12BPM) (the latter is considered within the range of normalised breathing; Tsai et al., 2015). The current online study is hosted within the Inquisit environment; initially participants will be presented with a study information page followed by a consent page. Subject to consent, participants will then complete the Penn-State Worry Questionnaire (PSWQ), a demographical questionnaire followed by self-assessment of baseline anxiety and relaxation levels, as measured by visual analogue scales (VAS). Participants will then receive a five-minute N-back practice block to aid with EF task familiarisation provided later on. During the N-back task, participants are required to respond (via keypress) when the stimulus on the current trial matches the stimulus N trials previously, typically one, two or three trials before. Once practice is complete, participants will be randomly assigned to a 5-minute self-paced breathing session, either the RFB or active control breathing condition (allocation is counter-balanced across participants). During self-paced breathing, participants are instructed to match their breathing rate to the speed of a visual cue on the screen (see below for further details). The visual cue consists of a blue bar rising (prompting inhalation) and a green bar lowering (prompting exhalation) (based on the EZ-Air software; Thought Technology Ltd., Montreal, Canada). Previous research suggests that 6BPM is an optimal breathing pace for evoking cardiac resonance (Laborde et al., 2021), whilst 12BPM is thought to be closer to our normative (although highly variable) breathing rate (Tsai et al., 2015). Once the self-paced breathing session is complete, participants rate their anxiety and relaxation levels, as well as their confidence in maintaining the required breathing pace throughout the block (included as a manipulation check). Finally, the main N-back task is immediately presented in order to minimize potential wash-out effects. The current study adopts a within-subject design; participants will therefore repeat the same procedure a second time starting from the breathing block. The breathing pacer will be for the alternate breathing condition from that seen in the first block; VAS ratings and the N-back will be unchanged. Overall, the study lasts approximately one hour. Executive Function Measure, the N-back task: Participants must indicate with a key press as quickly and as accurately as possible when the currently presented stimulus is identical to the stimulus presented N trials previously, typically zero-back, one-back, two-back and three-back (during the zero-back block, participants must decide whether the currently presented stimulus is identical to that shown on the very first target trial). Participants are provided with an instructional reminder before the start of a given N-back block. 20 different consonants are used as stimuli (Ragland et al., 2002), and the task consists of 3 blocks of 15 trials for each N-back ‘level’ (12 blocks in all) presented in pseudo-random order. Of the 15 trials in each block, 5 present a target (the current stimulus matches the N-trials back) and 10 present a nontarget (the current stimulus does not match the N-trials back), appearing in a randomised order. ‘Hits’ refer to those trials where participants have correctly identified the current stimulus as matching N trials previously, whereas ‘false alarms’ refer to those trials where participants have incorrectly identified the current stimulus as matching N trials previously. Self-paced breathing: As specified above, the self-paced breathing paradigm consists of two separate sessions, namely RFB (6BPM) and active control breathing (12BPM) conditions. During the session, participants are instructed to match their respiration rate to the speed of a visual cue located at the centre of the screen. The visual cue consists of a blue bar rising (prompting inhalation) and a green bar lowering (prompting exhalation). Participants are instructed to inhale through the nose and exhale through the mouth with pursed lips. RFB consists of an inhale-to-exhale ratio of 4.5-5.5 seconds whereas the 12 BPM condition consists of a ratio of 2.2-2.8 seconds, respectively. The self-paced breathing block lasts 5-minutes without any break (Laborde and colleagues (2022) implemented 5-minute RFB in conditions with and without HRV biofeedback). The animated pacer is presented on the instructional pages to aid familiarisation, and once participants have understood the instructions, they can begin the main session. Visual analogue scales (VAS): the VAS provides a measure of self-reported anxiety, relaxation and breathing efficacy. For the anxiety scale, participants are prompted with the question on the screen: ‘How anxious do you feel? (Click on the line)’ . The line is anchored by the words ‘not at all anxious’ at the extreme left of the line and ‘extremely anxious’ at the extreme right of the line, with a response range of 0 – 100; responses are not revealed to participants. This same scale is applied to the relaxation domain: ‘How relaxed do you feel? (Click on the line)’. The line is anchored by the words ‘not at all relaxed’ at the extreme left of the line and ‘extremely relaxed’ at the extreme right of the line. Finally, a third VAS serves as a manipulation check of self-paced breathing: ‘What percentage of the time did you successfully match your breathing with the pacer? (Click on the line)’. The line is anchored by the value ‘0 %’ at the extreme left of the line and ‘100%’ at the extreme right of the line. Previous research adopt VAS in RFB interventions (Laborde et al., 2021, 2022; Lin et al., 2014).