Zachary W. Bell

Perceptual and arterial occlusion responses to very low load blood flow restricted exercise performed to volitional failure

Studies examining perceptual and arterial occlusion responses between blood flow restricted exercise and high load exercise often prescribe an arbitrary number of repetitions, making it difficult for direct comparisons. Therefore, the purpose of this study was to compare these protocols when performed to volitional failure.

Changes in muscle size via MRI and ultrasound: Are they equivalent?

We read with great interest the recent study by Franchi et al1 which concluded that changes in muscle thickness measured via ultrasound tracked well with changes in anatomical crosssectional area measured via magnetic resonance imaging (MRI). While this is a very important study due to the widespread use of ultrasound in training studies, there may be a slightly more advantageous way to analyze the results. A correlation between the percentage change in muscle thickness and the percentage change in anatomical crosssectional area was computed, yielding a significant correlation (r = .69). This correlation appeared to be primarily driven by four limbs (likely from two individuals) detailing a major limitation with correlational analyses as they can be skewed by outliers and are reliant on sufficient variability in the data. We used a graph digitizer to estimate the values provided in the figure (Figure 4A of Franchi et al1) and computed the exact same correlation (r = .69), which was negated when excluding the four limbs that responded to a much greater extent than the rest (r = .34; P = .236). An alternative analysis exists through equivalency testing to assess whether the two measurements were not too different from one another.2 While a traditional t test examines whether a 95% confidence interval crosses zero when testing the difference between two groups, an equivalency test assesses whether the mean difference and 90% confidence interval lie entirely within the established boundaries (using a 90% confidence interval yields a 0.05 α for significance testing3). These boundaries must be established by the researcher prior to data collection, but a common method is to use half of the minimal difference.2 Importantly, this method allows for the comparison of values within the same individual and is not biased toward outliers, nor is it impacted by the level of variability in the data, as is the case for correlational analyses. Using the data set we obtained from Figure 4A of Franchi et al1 we ran an equivalency trial using 2.3% as the upper and lower boundaries as this corresponds to half of the minimal difference presented for muscle thickness (4.6%/2 = 2.3%). The results are detailed in Figure 1 and illustrate that ultrasound measured muscle thickness and MRI measured anatomical crosssectional area cannot be deemed equivalent. This appears to be primarily driven by the tendency of muscle growth to be greater when using ultrasound measured muscle thickness measurements, and this is evident given the mean difference (−2.1%; 90% confidence interval: −4.0, −0.3). Had there been no mean difference these measures would have been considered equivalent as the 90% confidence interval would lie entirely within the established boundaries (mean: 0; 90% confidence interval: −1.9, 1.8). Therefore, it appears that ultrasound measured muscle thickness and MRI measured crosssectional area track similarly; however, the ultrasound produces higher magnitudes of growth when expressed as a percentage. This may be an important

An investigation into setting the blood flow restriction pressure based on perception of tightness

OBJECTIVEnTo determine whether the perceived tightness scale could be used to set sub-occlusive blood flow restriction pressures. A secondary aim was to determine variables that may impact individual ratings.nnnAPPROACHnOne hundred and twenty participants completed three separate conditions in one limb within the upper and lower body. Participants were asked to rate their perceived tightness for two of the three conditions, regarded as moderate pressure without pain (7/10) and intense pressure with pain (10/10). A third condition, arterial occlusion pressure, was completed that required no rating from participants. Order of conditions and limb assignment were randomized for each participant. Measurements for muscle and fat thickness along with limb circumference were completed on the tested limbs.nnnMAIN RESULTSnOrder of conditions did not affect results in the upper or lower body. A condition effect was found for the upper body with the 7/10 rating lower than the arterial occlusion pressure [7/10: 132 (38) mmHgu2009u2009<u2009u2009Arterial Occlusion: 162 (24) mmHgu2009u2009<u2009u200910/10: 202 (46) mmHg]. A condition effect was also found for the lower body with 7/10 condition [120 (33) mmHg] rating lower than arterial occlusion pressure [171 (28) mmHg] and 10/10 condition [178 (49) mmHg]. However, there was a non-significant difference between the arterial occlusion pressure and the 10/10 condition (difference of 7(-3, 18) mmHg, (Pu2009u2009=u2009u20090.159).nnnSIGNIFICANCEnParticipants appear adept in their ability to rate sub-occlusive pressure based upon perceived tightness. Findings from this study provide some support for the utility of this method as a means for completion of practical blood flow restriction, whereby individuals tighten the cuff based upon their relative perceptual response.

The impact of ultrasound probe tilt on muscle thickness and echo-intensity: A cross-sectional study

INTRODUCTION/BACKGROUNDnTo determine the influence of ultrasound probe tilt on reliability and overall changes in muscle thickness and echo-intensity.nnnMATERIALS AND METHODSnThirty-six individuals had a total of 15 images taken on both the biceps brachii and tibialis anterior muscles. These images were taken in 2° increments with the probe tilted either upward (U) or downward (D) from perpendicular (0°) to the muscle (U6°, U4°, U2°, 0°, D2°, D4°, and D6°). All images were then saved, stored, and analyzed using Image-J software for echo-intensity and muscle thickness measures. Mean values (2-3 measurements within each probe angle) were compared across each probe angle, and reliability was assessed as if the first measure was taken perpendicular to the muscle, but the second measure was taken with the probe tilted to a different angle (to assume unintentional adjustments in reliability from probe tilt).nnnRESULTSnTilting the probe as little as 2° produced a significant 4.7%, and 10.5% decrease in echo-intensity of the tibialis anterior and biceps brachii muscles, respectively, while changes in muscle thickness were negligible (<1%) at all probe angles. The reliability for muscle thickness was greater than that of echo-intensity when the probe was held perpendicular at both measurements (∼1% vs 3%), and the impact that probe tilt had on reliability was exacerbated for echo-intensity measurements (max coefficient of variation: 24.5%) compared to muscle thickness (max coefficient of variation: 1.5%).nnnCONCLUSIONnWhile muscle thickness is less sensitive to ultrasound probe tilt, caution should be taken to ensure minimal probe tilt is present when taking echo-intensity measurements as this will alter mean values and reduce reliability. Echo-intensity values should be interpreted cautiously, particularly when comparing values across technicians/studies where greater alterations in probe tilt is likely.

Muscle Adaptations to High-Load Training and Very Low-Load Training With and Without Blood Flow Restriction

An inability to lift loads great enough to disrupt muscular blood flow may impair the ability to fatigue muscles, compromising the hypertrophic response. It is unknown what level of blood flow restriction (BFR) pressure, if any, is necessary to reach failure at very low-loads [i.e., 15% one-repetition maximum (1RM)]. The purpose of this study was to investigate muscular adaptations following resistance training with a very low-load alone (15/0), with moderate BFR (15/40), or with high BFR (15/80), and compare them to traditional high-load (70/0) resistance training. Using a within/between subject design, healthy young participants (n = 40) performed four sets of unilateral knee extension to failure (up to 90 repetitions/set), twice per week for 8 weeks. Data presented as mean change (95% CI). There was a condition by time interaction for 1RM (p < 0.001), which increased for 70/0 [3.15 (2.04,4.25) kg] only. A condition by time interaction (p = 0.028) revealed greater changes in endurance for 15/80 [6 (4,8) repetitions] compared to 15/0 [4 (2,6) repetitions] and 70/0 [4 (2,5) repetitions]. There was a main effect of time for isometric MVC [change = 10.51 (3.87,17.16) Nm, p = 0.002] and isokinetic MVC at 180°/s [change = 8.61 (5.54,11.68) Nm, p < 0.001], however there was no change in isokinetic MVC at 60°/s [2.45 (−1.84,6.74) Nm, p = 0.261]. Anterior and lateral muscle thickness was assessed at 30, 40, 50, and 60% of the upper leg. There was no condition by time interaction for muscle thickness sites (all p ≥ 0.313). There was a main effect of time for all sites, with increases over time (all p < 0.001). With the exception of the 30% lateral site (p = 0.059) there was also a main effect of condition (all p < 0.001). Generally, 70/0 was greater. Average weekly volume increased for all conditions across the 8 weeks, and was greatest for 70/0 followed by 15/0, 15/40, then 15/80. With the exception of 1RM, changes in strength and muscle size were similar regardless of load or restriction. The workload required to elicit these changes lowered with increased BFR pressure. These findings may be pertinent to rehabilitative settings, future research, and program design.

Moderately heavy exercise produces lower cardiovascular, RPE, and discomfort compared to lower load exercise with and without blood flow restriction

PurposeTo determine the acute cardiovascular and perceptual responses of low-load exercise with or without blood flow restriction and compare those responses to that of moderately heavy exercise.MethodsTwenty-two participants completed unilateral elbow flexion exercise with a moderately heavy-load- [70% one-repetition maximum (1RM); 70/0] and with three low-load conditions (15% 1RM) in combination with 0% (15/0), 40%, (15/40) and 80% (15/80) arterial occlusion pressure. Participants exercised until failure (or until 90 repetitions per set). The cardiovascular response (arterial occlusion) was measured pre and post exercise and the perceptual responses [ratings of perceived exertion (RPE) and discomfort] were determined before and after each set of exercise.ResultsFor arterial occlusion pressure, the lower-load conditions had greater change from pre to post compared to 70/00 (e.g., 15/80: 44 vs. 70/0: 34xa0mmHg). RPE was highest across the sets for the 15/80 condition with the other conditions having similar RPE (e.g., set 4: median rating of 17.2 for 15/80 vs. ~u200915.5 for other conditions). Ratings of discomfort were also greatest for the 15/80 condition (15/80u2009>u200915/40u2009>u200915/0u2009>u200970/0). Exercise volume within the 15/0 and 15/40 conditions were similar but were significantly greater than that observed with the 15/80 and 70/0 conditions.ConclusionLow-load exercise to volitional failure results in a greater cardiovascular response to that of moderately heavy-load exercise. When high pressure is applied to low load exercise, there is a reduction in exercise volume but an elevated perceptual response that may be an important consideration when applying this stimulus in practice.

Very Low Load Resistance Exercise in the Upper Body with and without Blood Flow Restriction: Cardiovascular Outcomes

It is proposed that, at very low loads, greater blood flow restriction (BFR) pressures might be required for muscular adaptation to occur. The cardiovascular and hyperemic response to very low loads combined with relative levels of BFR is unknown. Ninety-seven participants were recruited and assigned to 1 of 4 exercise conditions: 15% of 1-repetition maximum (1RM) without BFR (15/00), 15% 1RM with BFR at 40% of arterial occlusion pressure (AOP) (15/40), 15% of 1RM with BFR at 80% of AOP (15/80), and 70% of 1RM without BFR (70/00). Participants performed 4 sets of unilateral biceps curls. Blood pressure was measured before and after exercise; brachial artery blood flow was measured before exercise, following the second set, and 1 min following exercise. Systolic blood pressure increased following exercise in all conditions (+10 (11) mm Hg, P < 0.0005). Diastolic pressure increased in all but 70/00 (+2 (11) mm Hg, P = 0.107). Brachial artery blood flow increased following the second set of exercise in all but 15/80 (+43.4 (76.8) mL·min-1, P = 0.348). One minute following exercise and cuff deflation, there were no differences in blood flow between conditions (P > 0.05). Similarly, artery diameter was increased in all conditions except 15/80 (+0.002 (0.041) cm, P = 0.853) following the second set, and increased in all conditions by 1 min following exercise (P < 0.05). In conclusion, exercise-induced hyperemia is blunted with increasing pressures of BFR. There is a modest increase in blood pressure at very low loads of resistance exercise in the upper body.