Perceptual, Hemodynamic and Cardiovascular Responses of Two Different BFR Training Protocols

BFR training is growing in popularity and a variety of devices are on the market for clinical use. One way in which it is thought that BFR resistance training safety can be increased is by using a BFR cuff that regulates the applied pressure to the limb during each repetition. This is thought to reduce perceptual, hemodynamic and cardiovascular responses to non-autoregulated approaches, theoretically increasing long-term compliance and safety with BFR training.

However, only one study has directly compared the effect of an autoregulated vs. non-autoregulated and their design did not standardize the cuff width between the autoregulated and the non-autoregulated cuff, potentially leading to differences in observed outcomes. That study concluded that autoregulated cuffs better manage the hemodynamic and perceptual responses to non-failure training protocols while providing a more accurate cuff-limb interface pressure, thus increasing safety profile. Moreover, BFR resistance training is commonly performed to failure so it is unknown whether the use of regulated pressures influences fatiguability or alters perceptual, cardiovascular and hemodynamic responses compared to a non-autoregulated cuff.

Therefore, the purpose of this study is to compare the perceptual, hemodynamic and cardiovascular responses using either an autoregulated pressure or a non-autoregulated pressure during a 20% 1RM leg extension non-failure and failure protocol in healthy, recreationally active male and female participants (without any history of BFR training) using the SmartTools Pro model (a device able to be autoregulated and non-autoregulated based on setting, providing an ability to directly compare autoregulation to non-autoregulation with a cuff of similar width).

Each participant will perform one familiarization session to determine 1RM, take baseline data for participant characteristics including limb occlusion pressure and relevant hemodynamic and cardiovascular measures, acclimate to the non-failure protocol without blood flow restriction and anchor perceptual baselines. Following familiarization session and at least 6 days between sessions, the dominant leg of each participant will be randomized to either the autoregulated or non-autoregulated pressure setting. Each participant will perform 4 sets of exercise applied in a continuous application setting using a commonly recommended protocol of 30-15-15-15 using a 2 second concentric/2 second eccentric tempo with 30-45 seconds of interset rest. The BFR cuff will either be set to autoregulation or non-autoregulated pressure setting. Following completion of the protocol, with the cuffs still inflated, all variables will be assessed again before deflating. Participants will return to the lab at least 6 days later at a similar time and perform the same protocol with the opposite condition.

To assess the differences in all relevant outcome measures during a failure routine, the same protocol will be completed 6 days later with each participant randomized to either the autoregulated or non-autoregulated group. Participants will complete a similar resistance training program using 4 sets to volitional fatigue instead of the non-failure protocol. The data provided within this study could greatly inform clinical practice if responses to non-autoregulated cuff applications in both non-failure and failure routines are heightened compared to autoregulated cuff applications. This study will also provide preliminary data for application in clinical populations such as those with knee osteoarthritis as well as applying a similar strategy to healthy populations in the upper extremity to determine if similar responses exist between limbs.