Jones, Malcolm J.; Dominguez, Jesus F.; Macatugal, Clarizzah; Coleman, Keairez; Reed, Bryan; Schroeder, E. T.

Journal of Strength and Conditioning Research 37(1):p 55-61, January 2023., DOI: 10.1519/JSC.0000000000004211

PURPOSE:

A key principle of hamstring injury rehabilitation is developing high eccentric force ability through resistance training (RT) but it can take months before high-load RT is deemed safe and appropriate for rehabilitating serious hamstring injuries.

Low-load blood flow restriction (BFR) RT has been identified as an effective alternative when high-load RT is contraindicated but has been rarely studied relative to the hamstring muscles.

To address this, it was sought to compare the effect of longitudinal BFR RT with traditional RT on eccentric hamstring power, strength, lean mass, perceived soreness, and acute muscle swelling in healthy adults (n = 40 @ 19 F & 21 M).

Compared were low-load (30% 1-RM) eccentric lower extremity training with BFR (BFR-ELET) with traditional high-load (80% 1-RM) eccentric lower extremity training (TRAD-ELET) without BFR biweekly for 6 weeks.

PROCEDURES:

Subjects were randomized to determine which leg would be assigned to the BFR-ELET conditions using a random number generator. The contralateral leg was trained traditionally in the TRAD-ELET intervention. Workouts were performed on a leg curl machine.

Before training, the pressure at which 80% of arterial blood flow was occluded in the upper leg was determined for the BFR-ELET leg using a Delfi Personal Tourniquet System (Delfi, Vancouver, BC) for BFR.

To isolate eccentric muscle contractions of the hamstring, subjects were assisted by a trainer for the concentric (raising) knee flexion phase of the unilateral leg curl exercise until the knee reached 90 degrees of flexion, then allowed to complete the eccentric (lowering ) contraction independently.

Subjects completed the eccentric phase unassisted and spent approximately 3 seconds to reach full knee extension.

Each training day the subjects' BFR-ELET occurred first at 30% of 1-RM for 4 sets of 30/15/15/15 repetitions. A 30-second rest period was used between sets and tourniquet inflation was maintained the entire time including rest periods.

Following a 3-minute rest, subject TRAD-ELET training occurred on the contralateral leg at 80% of 1-RM for 3 sets of 10 repetitions with 30 seconds of rest between sets compared to traditional RT with BFR training. No tourniquet was used for TRAD-ELET and the volume remained consistent for both protocols.

Preintervention baseline tests that included eccentric hamstring muscle power, strength, and muscle measures were also completed within 5 days before starting the training program. Sessions were completed 2 times a week for 6 weeks.

Post testing was completed one day after the program concluded.

CONCLUSIONS:

Both protocols showed dependent variable outcomes that did not differ significantly except for muscle swell assessed by bioelectrical impedance analysis, which decreased significantly more in the BFR-ELET condition compared with TRAD-ELET.

Therefore, the findings support BFT-ELET as an effective alternative to TRAD-ELET for improving strength and myocellular swelling as a potential mediator for strength outcomes associated with BFR training.

IN PLAIN ENGLISH:

Because no significant differences in the eccentric hamstring performance gains between novel low-load BFR-ELET and current standard of care high-load TRAD-ELET there may be a place for BFR training provided it is performed safely.

Conventional training programs used for hamstring strengthening usually use a minimum of 70% of an athlete's 1-RM and still works but using BFR training with loads as low as 30% of a 1-RM does lessen the external load which can lower joint stress and may be useful when rehabbing an injury or returning to training post-surgery.