Discomfort, Fatigue, and Lactate Responses to Different Restrictive Pressures during Knee Extension Exercise

Abstract

PURPOSE: To investigate the effects of different restrictive pressures by changing the level of air and tightness of blood flow restriction (BFR) cuffs on 1) maximum voluntary contraction (MVC) of quadriceps muscles, 2) heart rate (HR), blood pressure (BP), blood lactate (LA), rate of perceived exertion (RPE), and discomfort response during bilateral knee extension exercise. METHODS: Sixteen male subjects (between the ages of 18 and 50) were familiarized with the study protocol and had their leg strength (one repetition maximum, 1RM) and thigh circumference (THC) measured on the first day. Different restrictive pressures such as the final pressure (FP, pressure created by inflation) and initial pressure (IP, pressure created by tightness of cuffs before inflation) were used. The three, randomized, sessions: 1) an additional 20 mmHg over the recommended FP (based on THC) with an IP of 50 mmHg ([email protected]+20), 2) with a subtraction of 20 mmHg from the recommended FP with an IP of 65 mmHg ([email protected]), 3) the recommended FP with an IP of 50 mmHg. Each condition began with a warm-up prior to pre-MVC. Upon completing pre-MVC testing, subjects were fitted with BFR cuffs at the most proximal part of their legs, which were tightened and inflated corresponding to a random session. Once the cuffs were inflated, the subjects performed bilateral knee extension exercises at 20% 1RM for 4 sets (30, 15, 15, 15 reps) with a 30 sec rest between sets 1-2 and 3-4; and a 1 min rest between sets 2-3. Following the last set, subjects performed a post-MVC and the BFR cuffs were taken off immediately after post-MVC. LA and BP were measured before, mid, and immediately, 5, and 15 min post exercise. HR, RPE, and discomfort were measured before and after each set. RESULTS: There were condition (p=0.02) and time (p<0.01) main effects for HR; and condition (p<0.02) and time (p<0.01) main effects for MVC. There were also significant time main effects for systolic BP, RPE, discomfort, LA, and diastolic BP (p<.01). CONCLUSIONS: The results suggest that different pressure settings did not change discomfort level, but [email protected]+20 induced the highest HR and [email protected] caused the greatest level of fatigue. Depending on what clinical outcome is desired, a specific tightness and inflation of the BFR cuffs may be used.