Patterns of responses and time-course of changes in muscle size and strength during low-load blood flow restriction resistance training in women

Purpose The purpose of this investigation was to examine the individual and composite patterns of responses and time-course of changes in muscle size, strength, and edema throughout a 4 week low-load blood flow restriction (LLBFR) resistance training intervention. Methods Twenty recreationally active women (mean ± SD; 23 ± 3 years) participated in this investigation and were randomly assigned to 4 weeks (3/week) of LLBFR ( n = 10) or control ( n = 10) group. Resistance training consisted of 75 reciprocal isokinetic forearm flexion–extension muscle actions performed at 30% of peak torque. Strength and ultrasound-based assessments were determined at each training session. Results There were quadratic increases for composite muscle thickness ( R 2 = 0.998), concentric peak torque ( R 2 = 0.962), and maximal voluntary isometric contraction (MVIC) torque ( R 2 = 0.980) data for the LLBFR group. For muscle thickness, seven of ten subjects exceeded the minimal difference (MD) of 0.16 cm during the very early phase (laboratory visits 1–7) of the intervention compared to three of ten subjects that exceeded MD for either concentric peak torque (3.7 Nm) or MVIC (2.2 Nm) during this same time period. There was a linear increase for composite echo intensity ( r 2 = 0.563) as a result of LLBFR resistance training, but eight of ten subjects never exceeded the MD of 14.2 Au. Conclusions These findings suggested that the increases in muscle thickness for the LLBFR group were not associated with edema and changes in echo intensity should be examined on a subject-by-subject basis. Furthermore, LLBFR forearm flexion–extension resistance training elicited real increases in muscle size during the very early phase of training that occurred prior to real increases in muscle strength.