The addition of blood flow restriction during resistance exercise does not increase prolonged low-frequency force depression

Abstract

At a given exercise intensity, blood flow restriction (BFR) reduces the volume of exercise required to impair post-exercise neuromuscular function. Compared to traditional exercise, the time course of recovery is less clear. After strenuous exercise, force output assessed with electrical muscle stimulation is impaired to a greater extent at low versus high stimulation frequencies, a condition known as prolonged low-frequency force depression (PLFFD). It is unclear if BFR increases PLFFD after exercise. This study tested if BFR during exercise increases PLFFD and slows recovery of neuromuscular function compared to regular exercise. Fifteen physically active participants performed six low-load sets of knee-extensions across four conditions: resistance exercise to task failure (RE_TF), resistance exercise to task failure with BFR applied continuously (BFR_CONT) or intermittently (BFR_INT), and resistance exercise matched to the lowest exercise volume condition (RE_VM). Maximal voluntary contraction (MVC) force output, voluntary activation and a force-frequency (1-100 Hz) curve were measured before and 0, 1, 2, 3, 4 and 24 h after exercise. Exercise to task failure caused similar reductions at 0 h for voluntary activation (RE_TF = 81.0 ± 14.2%, BFR_INT = 80.9 ± 12.4% and BFR_CONT = 78.6 ± 10.7%) and MVC force output (RE_TF = 482 ± 168 N, BFR_INT = 432 ± 174 N, and BFR_CONT = 443 ± 196 N), which recovered to baseline values between 4 and 24 h. PLFFD occurred only after RE_TF at 1 h supported by a higher frequency to evoke 50% of the force production at 100 Hz (1 h: 17.5 ± 4.4 vs. baseline: 15 ± 4.1 Hz, P = 0.0023), BFR_INT (15.5 ± 4.0 Hz; P = 0.03), and RE_VM (14.9 ± 3.1 Hz; P = 0.002), with a trend versus BFR_CONT (15.7 ± 3.5 Hz; P = 0.063). These findings indicate that, in physically active individuals, using BFR during exercise does not impair the recovery of neuromuscular function by 24 h post-exercise.

Keywords: PLFFD; ischaemia; oxygen availability; volitional fatigue.

FIGURE 1

Study overview. (a) Introductory, characterization and blood flow restriction (BFR) familiarization visit. (b) Intervention visit overview with all baseline and post‐exercise neuromuscular testing. Participants performed six sets of knee‐extensions with 20% of their one repetition maximum (1‐RM) under the following conditions: low‐load resistance exercise to task failure (RE_TF), low‐load resistance exercise to task failure with BFR applied continuously (BFR_CONT), low‐load resistance exercise to task failure with BFR applied intermittently during exercise sets (BFR_INT), and low‐load resistance exercise volume matched (RE_VM) to the condition with the lowest total number of repetitions. (c) Representative tracing of the isometric strength and voluntary activation test (left) as well as the raw force–frequency tracings (right inset). The graph on the right represents the non‐linear regression curve fitting analysis to determine the frequency required to evoke 50% of the force output at 100 Hz. The figure was created using BioRender.com.

FIGURE 2

(a, b) Total exercise repetitions (a) and volume (repetitions × load; b) performed after the six sets for low‐load resistance exercise to task failure (RE_TF; black bars or circles), low‐load resistance exercise to task failure with BFR applied intermittently during exercise sets (BFR_INT; blue bars or circles), low‐load resistance exercise to task failure with BFR applied continuously (BFR_CONT; maroon bars or circles), and low‐load resistance exercise volume matched (RE_VM; grey bars or circles) to the condition with the lowest total number of repetitions. The colour of each asterisk represents the condition that is significantly different from RE_TF or BFR_INT. Data are expressed as means + standard deviation with the white circles representing individual participants (n = 15/condition). (c, d) Maximum voluntary contraction force (c) and voluntary activation (d) at baseline and during the 0–24 h recovery period after each condition. ANOVA P‐values with partial eta (η_p ²) are provided in each panel. Data are expressed as means + standard deviation (n = 14/condition). *P < 0.05 versus baseline; †P < 0.05 versus RE_VM at the same time point; (†)P = 0.062 versus RE_VM at the same time point; ‡P < 0.05 versus RE_TF at the same time point. The colour of each symbol represents significantly different conditions. All individual responses can be found in the Supporting information.

FIGURE 3

Peak force output, half‐relaxation time, and relative half‐relaxation rate for potentiated twitch contractions (a–c) or tetanic (100 Hz) contractions (d–f) at baseline and 0–24 h after six sets of low‐load resistance exercise to task failure (RE_TF; black circles), low‐load resistance exercise to task failure with BFR applied intermittently during exercise sets (BFR_INT; blue circles), low‐load resistance exercise to task failure with BFR applied continuously (BFR_CONT; maroon circles), and low‐load resistance exercise volume matched (RE_VM; grey circles) to the condition with the lowest total number of repetitions. ANOVA P‐values with partial eta (η_p ²) are provided in each panel. *P < 0.05 versus baseline; †P < 0.05 versus RE_VM at the same time point; ‡P < 0.05 versus RE_TF at the same time point. The colour of each symbol represents significantly different conditions. Data are expressed as means + standard deviation (n = 15/condition). All individual responses can be found in the Supporting information.

FIGURE 4

Peak absolute force output at 1 Hz (a), 5 Hz (b), 8 Hz (c), 10 Hz (d), 20 Hz (e), 50 Hz (f), and 100 Hz (g) of stimulation delivered over 1 s at baseline and 0–24 h after six sets of low‐load resistance exercise to task failure (RE_TF; black circles), low‐load resistance exercise to task failure with BFR applied intermittently during exercise sets (BFR_INT; blue circles), low‐load resistance exercise to task failure with BFR applied continuously (BFR_CONT; maroon circles), and low‐load resistance exercise volume matched (RE_VM; grey circles) to the condition with the lowest total number of repetitions. ANOVA P‐values with partial eta (η_p ²) are provided in each panel. *P < 0.05 versus baseline; (*)P = 0.062 versus baseline; †P < 0.05 versus RE_VM at the same time point; ‡P < 0.05 versus RE_TF at the same time point; ωP < 0.05 versus BFR_INT at the same time point. The colour of each symbol represents a significantly different condition. Data are expressed as means + standard deviation (n = 15/condition). All individual responses can be found in the Supporting information.

FIGURE 5

(a, b) The time course recovery of the 10/100 Hz force output (a) and the frequency required to elicit 50% of the force at 100 Hz (Frequency₅₀; b) after six sets of low‐load resistance exercise to task failure (RE_TF; black lines and circles), low‐load resistance exercise to task failure with BFR applied intermittently during exercise sets (BFR_INT; blue lines and circles), low‐load resistance exercise to task failure with BFR applied continuously (BFR_CONT; maroon lines and circles), and low‐load resistance exercise volume matched (RE_VM; grey lines and circles) to the condition with the lowest total number of repetitions. The Frequency₅₀ was determined using non‐linear regression analysis. ANOVA P‐values with partial eta (η_p ²) are provided. (c) Relative force–frequency curves to illustrate the rightward shift 0 h post‐exercise (dashed lines) and 1 h post‐exercise (dotted lines) compared to baseline (continuous lines). Symbols and error bars are omitted for clarity. The mean values and the variance of the relative force output for each frequency can be found in Table 2. *P < 0.05 versus baseline; †P < 0.05 versus RE_VM at the same time point; ‡P < 0.05 versus RE_TF at the same time point; (‡)P = 0.063 versus RE_TF at the same time point; ωP < 0.05 versus BFR_INT at the same time point. The colour of each symbol represents a significantly different condition. Data are expressed as means + standard deviation (n = 15/condition). All individual responses can be found in the Supporting information.