Is there evidence for the asymmetrical transfer of strength to an untrained limb?

PURPOSE: The literature predominantly addresses cross-education of strength in the dominant limb rather than the non-dominant limb, guided by the hypothesis of an asymmetrical transfer of strength from unilateral training protocols. The purpose of the study was to review the literature and determine how much evidence was available to support this claim. A meta-analysis was performed to estimate the magnitude of this hypothesized asymmetrical transfer of strength. METHODS: A literature search of all possible records was implemented using Cochrane Library, PubMed, and Scopus from February 2022 to May 2022. Comparison of randomized controlled trials was computed. The change scores and standard deviations of those change scores were extracted for each group. Only three studies met the criteria, from which a total of five effect sizes were extracted and further analyzed. RESULTS: The overall effect of resistance training of the dominant limb on strength transfer to the non-dominant limb relative to the effects of resistance training the non-dominant limb on strength transfer to the dominant (non-training) limb was 0.46 (SE 0.42). The analysis from this study resulted in minimal support for the asymmetry hypothesis. Given the small number of studies available, we provide the effect but note that the estimate is unlikely to be stable. CONCLUSION: Although it is repeatedly stated that there is an asymmetrical transfer of strength, our results find little support for that claim. This is not to say that it does not exist, but additional research implementing a control group and a direct comparison between limbs is needed to better understand this question.

Blood flow restriction augments the cross-education effect of isometric handgrip training.

INTRODUCTION: The application of blood flow restriction (BFR) to low-intensity exercise may be able to increase strength not only in the trained limb but also in the homologous untrained limb. Whether this effect is repeatable and how that change compares to that observed with higher intensity exercise is unknown. PURPOSE: Examine whether low-intensity training with BFR enhances the cross-education of strength compared to exercise without BFR and maximal efforts. METHODS: A total of 179 participants completed the 6-week study, with 135 individuals performing isometric handgrip training over 18 sessions. Participants were randomly assigned to one of four groups: 1) low-intensity (4 × 2 min of 30% MVC; LI, n = 47), 2) low-intensity with blood flow restriction (LI + 50% arterial occlusion pressure; LI-BFR, n = 41), 3) maximal effort (4 × 5 s of 100% MVC; MAX, n = 47), and 4) non-exercise control (CON, n = 44). RESULTS: LI-BFR was the only group that observed a cross-education in strength (CON: 0.64 SD 2.9 kg, LI: 0.95 SD 3.6 kg, BFR-LI: 2.7 SD 3.3 kg, MAX: 0.80 SD 3.1 kg). In the trained hand, MAX observed the greatest change in strength (4.8 SD 3.3 kg) followed by LI-BFR (2.8 SD 4.0 kg). LI was not different from CON. Muscle thickness did not change in the untrained arm, but ulna muscle thickness was increased within the trained arm of the LI-BFR group (0.06 SD 0.11 cm). CONCLUSION: Incorporating BFR into low-intensity isometric training led to a cross-education effect on strength that was greater than all other groups (including high-intensity training).

Blood flow restriction augments exercise-induced pressure pain thresholds over repetition and effort matched conditions.

We sought to determine the effects of blood flow restriction (BFR) on exercise-induced hypoalgesia, specifically using low-load (LL) resistance exercise (30% 1RM) protocols that accounted for each individual's local muscular endurance capabilities. Forty-four participants completed four conditions: (1) 70% of maximal BFR repetitions with blood flow restriction (LL+BFR exercise); (2) 70% maximal BFR repetitions without LL+BFR (LL exercise); (3) 70% maximal free flow repetitions (LL+EFFORT exercise); (4) time-matched, non-exercise control (CON). Pressure pain threshold (PPT) was measured before and after exercise. Ischaemic pain threshold and tolerance was assessed only at post. The change in upper body PPT was greater for LL+BFR exercise compared to LL exercise [difference of 0.15 (0.35) kg/cm2], LL+EFFORT exercise [difference of 0.23 (0.45) kg/cm2], and the CON condition. The change in lower body PPT was greater for LL+BFR exercise compared to LL exercise [difference of 0.40 (0.55) kg/cm2], LL+EFFORT exercise [difference of 0.36 (0.62) kg/cm2], and the CON condition. Ischaemic pain thresholds and tolerances did not change. Submaximal exercise with BFR resulted in systemic increases in PPT but had no influence on ischaemic pain sensitivity. This effect is likely unique to BFR as we did not see changes in the effort matched free flow condition.

The Impact of Different Ischemic Preconditioning Pressures on Pain Sensitivity and Resistance Exercise Performance.

ABSTRACT: Kataoka, R, Song, JS, Yamada, Y, Hammert, WB, Seffrin, A, Spitz, RW, Wong, V, Kang, A, and Loenneke, JP. The impact of different ischemic preconditioning pressures on pain sensitivity and resistance exercise performance. J Strength Cond Res 38(5): 864-872, 2024-To determine (a) the impact of ischemic preconditioning pressures (applied as a % of arterial occlusion pressure [AOP]) on pressure pain threshold (PPT) and resistance exercise performance and (b) whether changes in performance could be explained by changes in PPT. Subjects ( n = 39) completed 4 protocols in a randomized order: (a) ischemic preconditioning (IPC) at 110% AOP (IPC 110%), (b) IPC at 150% AOP (IPC 150%), (c) IPC at 10% AOP (Sham), and (d) time-matched control (CON). Each protocol included 4 cycles of 5 minutes of occlusion followed by 5 minutes of reperfusion. Pressure pain threshold was taken before and after. Discomfort ratings were given at the end of each cycle. Every visit finished with 2 sets of 75-second maximal isokinetic unilateral elbow flexion or extension. Overall, IPC 110% and IPC 150% resulted in similar increases in PPT relative to CON [110%: difference of 0.36 (0.18, 0.54) kg·m -2 ; 150%: difference of 0.377 (0.15, 0.59) kg·m -2 ] and Sham. Both resulted in greater discomfort than Sham and CON, with IPC 150% inducing greater discomfort than IPC 110% (BF 10 : 14.74). There were no differences between the conditions for total work (BF 10 : 0.23), peak torque (BF 10 : 0.035), or average power (BF 10 : 0.159). We did not find evidence that PPT mediated performance. We did not detect changes in performance with 2 different relative pressures greater than AOP. Our mean applied pressures were lower than those used previously. There might be a minimal level of pressure (e.g., >150% of AOP) that is required to induce ergogenic effects of ischemic preconditioning.

Sex segregation in strength sports: Do equal-sized muscles express the same levels of strength between sexes?

OBJECTIVES: Concerns have been raised against the current two-sex binary category in sports competitions. The thesis states that if males and females were separated based on muscle size, it would negate the strength advantage between the sexes. We tested the possible sex differences in various strength outcomes when pair-matched for muscle thickness. METHODS: A total of 16 different data sets (n = 963) were assessed to pair-match females with males who had a muscle thickness value within 2%. We further compared the competition performances of the smallest male weight class within the International Powerlifting Federation (IPF) to different weight classes in females. RESULTS: Overall, 76%-88% of the strength assessments were greater in males than females with pair-matched muscle thickness, regardless of contraction types (i.e., isotonic, isometric, isokinetic). Additionally, males in the lightest weight division in the IPF largely outperformed females in heavier weight divisions. CONCLUSIONS: Our results would suggest that segregation based on muscle mass or surrogates of muscle mass (e.g., lean body mass) might not be an appropriate classification to create fair competition within strength sports. This is not to refute the concept of the desegregation of the two-sex binary category but to present data that raises important concerns about the potential sex-based differences in strength performance.

Potential considerations with estimating blood flow restriction pressure in the lower body using a narrower cuff.

Blood flow restriction pressures are typically set as a percentage of the arterial occlusion pressure. For those who do not have the ability to measure the arterial occlusion pressure, estimation equations are available. However, notable considerations are needed when estimating pressure with a narrow cuff (5 cm) in the lower body. A previously published equation in this journal was developed but was created only using 55% of the sample because the arterial occlusion of the others could not be obtained within the manufacturer's pressure limit. The purpose of this article was twofold: (1) to investigate how previous studies have implemented the equation and (2) to highlight potential concerns of using this equation. Two databases were used to locate articles that used the equation from Loenneke et al. (2015). We found that this equation had been cited 10 times to estimate arterial occlusion pressure with some notable concerns. Some did not use a 5 cm wide cuff, while others used it for participants who had arterial occlusion pressures exceeding 300 mmHg. To highlight the latter, we also applied the Loenneke et al. (2015) lower body equation to participants with arterial occlusion pressures known to exceed 300 mmHg to demonstrate potential concerns. This retrospective analysis found that 52% of the sample with known pressures over 300 mmHg (40 out of 77) would be estimated below 300 mmHg. This paper highlighted important considerations for those trying to estimate arterial occlusion pressure in the lower body with a narrow cuff (5 cm).

Effect of Increased Pressure Pain Threshold on Resistance Exercise Performance With Blood Flow Restriction.

ABSTRACT: Kataoka, R, Song, JS, Bell, ZW, Wong, V, Spitz, RW, Yamada, Y, and Loenneke, JP. Effect of increased pressure pain threshold on resistance exercise performance with blood flow restriction. J Strength Cond Res 37(6): 1204-1210, 2023-This study aimed to examine whether increasing pressure pain threshold (PPT) through isometric handgrip exercise (HG) affects the number of repetitions completed and discomfort with knee extension exercise (KE) with blood flow restriction (BFR), and examine whether performing additional exercise leads to a further increase in PPT. Forty-one participants completed 2 trials: rest followed by low-load KE with BFR at 80% of resting arterial occlusion pressure (Rest + KE BFR) and low-intensity (30% of maximal strength) HG exercise followed by KE with BFR (HG + KE BFR). Pressure pain threshold was measured before and after exercise at the forearm and tibialis anterior. Results are presented as median difference (95% credible interval). Pressure pain threshold increased at the forearm (Bayes factor [BF 10 ]: 5.2 × 10 7 ) and tibialis anterior (BF 10 : 1.5 × 10 6 ) after HG exercise. However, this did not lead to greater repetitions being completed with BFR exercise (0.2 [-0.1, 0.6] repetitions, BF 10 : 0.07). Pressure pain threshold after BFR exercise was not augmented over that observed with HG exercise (0.02 [-0.15, 0.2] kg·cm -2 , BF 10 : 0.175) at the forearm. More data are needed in the lower body to determine which model best fits the data (BF 10 : 0.84). Discomfort with BFR exercise was not different between conditions (1.0 [-2.3, 4.4] arbitrary units, BF 10 : 0.10). The pain-reducing effect of prior exercise did not change the repetitions completed with BFR exercise, suggesting that the change in PPT may not have been great enough to alter performance. Performing additional exercise did not elicit further increases in PPT nor was perceived discomfort to BFR exercise altered by changes in PPT.

Hypoalgesia following isometric handgrip exercise with and without blood flow restriction is not mediated by discomfort nor changes in systolic blood pressure.

The purpose was to examine the effect of isometric handgrip exercise with and without blood flow restriction on exercise-induced hypoalgesia at a local and non-local site, and its underlying mechanisms. Sixty participants (21 males & 39 females, 18-35 years old) completed 3 trials: four sets of 2-minute isometric handgrip exercise at 30% of maximum handgrip strength; isometric handgrip exercise with blood flow restriction at 50% of arterial occlusion pressure; and a non-exercise time-matched control. Pain thresholds increased similarly in both exercise conditions at a local (exercise conditions: ~0.45 kg/cm2, control: ~-0.04 kg/cm2) and non-local site (exercise conditions: ~0.37 kg/cm2, control: ~-0.16 kg/cm2). Blood flow restriction induced greater feelings of discomfort compared to exercise alone [median difference (95% credible interval) of 4.5 (0.5, 8.6) arbitrary units]. Blood pressure increased immediately after exercise (systolic: 10.3 mmHg, diastolic: 7.7 mmHg) and decreased in recovery. There was no within participant correlation between changes in discomfort and pressure pain threshold. A bout of isometric handgrip exercise with or without blood flow restriction can provide exercise-induced hypoalgesia at a local and non-local site. However, discomfort and changes in systolic blood pressure do not explain this response.

Can Individuals Be Taught to Sense the Degree of Vascular Occlusion? A Comparison of Methods and Implications for Practical Blood Flow Restriction.

ABSTRACT: Bell, ZW, Spitz, RW, Wong, V, Yamada, Y, Song, JS, Abe, T, and Loenneke, JP. Can individuals be taught to sense the degree of vascular occlusion? A comparison of methods and implications for practical blood flow restriction. J Strength Cond Res 36(12): 3359-3365, 2022-The study objective was to determine whether subjects could be conditioned to a relative blood flow restriction pressure in the lower body and compare 2 separate conditioning methods (unconstrained vs. constrained). Thirty-five subjects completed 4 visits, involving measurements for arterial occlusion and pressure estimations at 5 minutes and 24 hours after conditioning. The constrained method involved applying 40% of measured arterial occlusion 11 times, along with 10% above and below this pressure. The unconstrained method was time-matched, involving a series of inflations to 40% arterial occlusion for 12 seconds and then deflated for 22 seconds. Data are presented as mean differences (95% credible interval) unless otherwise noted. The absolute error between conditioning methods was found to be similar at 5 minutes (-1.1 [-5.9, 3.7] mm Hg) and 24 hours (-2.4 [-7, 2.2] mm Hg) after conditioning. The constant error differed between methods at 5 minutes [-8.2 (-14.4, -1.9) mm Hg] but was similar at 24 hours (-2.5 [-8.5, 3.6] mm Hg; H0: 0.680; H1: 0.068; and H2: 0.252) after conditioning. The bias and 95% limits of agreement for the unconstrained method were -3.9 (-33.8, 25.9) mm Hg at 5 minutes and -2.9 (-32, 26.1) mm Hg at 24 hours. The agreement for the constrained method was 4.2 (-28, 36.5) mm Hg at 5 minutes and -0.54 (-37.3, 36.2) mm Hg at 24 hours. Conditioning methods produced similar levels of absolute error, indicating that either method may offer a viable means of pressure application. Most estimates were between 20 and 60% of arterial occlusion pressure. Additional conditioning sessions may be needed to narrow this range at the individual level.

Cartilage Regeneration Using Human Umbilical Cord Blood Derived Mesenchymal Stem Cells: A Systematic Review and Meta-Analysis.

Background and Objectives: Human umbilical-cord-blood-derived mesenchymal stem cells (hUCB-MSCs) have recently been used in clinical cartilage regeneration procedures with the expectation of improved regeneration capacity. However, the number of studies using hUCB-MSCs is still insufficient, and long-term follow-up results after use are insufficient, indicating the need for additional data and research. We have attempted to prove the efficacy and safety of hUCB-MSC treatment in a comprehensive analysis by including all subjects with knee articular cartilage defect or osteoarthritis who have undergone cartilage repair surgery using hUCB-MSCs. We conducted a meta-analysis and demonstrated efficacy and safety based on a systematic review. Materials and Methods: This systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. For this study, we searched the PubMed, Embase, Web of Science, Scopus, and Cochrane Library literature databases up to June 2022. A total of seven studies were included, and quality assessment was performed for each included study using the Newcastle−Ottawa Quality Assessment Scale. Statistical analysis was performed on the extracted pooled clinical outcome data, and subgroup analyses were completed. Results: A total of 570 patients were included in the analysis. In pooled analysis, the final follow-up International Knee Documentation Committee (IKDC) score showed a significant increase (mean difference (MD), −32.82; 95% confidence interval (CI), −38.32 to −27.32; p < 0.00001) with significant heterogeneity (I2 = 93%, p < 0.00001) compared to the preoperative score. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at final follow-up were significantly decreased (MD, 30.73; 95% CI, 24.10−37.36; p < 0.00001) compared to the preoperative scores, with significant heterogeneity (I2 = 95%, p < 0.00001). The visual analog scale (VAS) score at final follow-up was significantly decreased (MD, 4.81; 95% CI, 3.17−6.46; p < 0.00001) compared to the preoperative score, with significant heterogeneity (I2 = 98%, p < 0.00001). Two studies evaluated the modified Magnetic Resonance Observation of Cartilage Repair Tissue (M-MOCART) score and confirmed sufficient improvement. In a study analyzing a group treated with bone marrow aspiration concentrate (BMAC), there was no significant difference in clinical outcome or M-MOCART score, and the post-treatment International Cartilage Repair Society (ICRS) grade increased. Conclusion: This analysis demonstrated the safety, efficacy, and quality of repaired cartilage following hUCB-MSC therapy. However, there was no clear difference in the comparison with BMAC. In the future, comparative studies with other stem cell therapies or cartilage repair procedures should be published to support the superior effect of hUCB-MSC therapy to improve treatment of cartilage defect or osteoarthritis.

The Relationship Between Muscle Size and Strength Does not Depend on Echo Intensity in Healthy Young Adults.

Muscle quality is typically defined as muscle strength relative to muscle size. Echo intensity has gained popularity as an index of skeletal muscle quality. There is common agreement that muscle size is related to strength at baseline and echo intensity is purported to impact this relationship. Thus, the purpose of this study was to examine whether echo intensity can be used as a physiological marker for muscle quality by investigating the moderating effect of echo intensity on the relationship between muscle size and strength. A sample of 96 participants was used for the upper body analysis and a separate sample of 96 participants was used for the lower body analysis. Echo intensity, muscle thickness, and strength measurements were measured on each limb. For strength, participants performed unilateral elbow flexion (upper body analysis) and knee extension (lower body analysis) to quantify 1-repetition maximum. Muscle thickness and echo intensity were determined from images captured using B-mode ultrasound. Muscle size correlated with muscle strength for all limbs. However, the relationship between muscle size and strength was not significantly moderated by echo intensity for Arm 1 (b = 0.042, p = 0.54) or Arm 2 (b = -0.002, p = 0.97). At the proximal site, no significant moderating effect of echo intensity was found in Leg 1 (b = 0.037, p = 0.67) or Leg 2 (b = -0.085, p = 0.29). Similarly, no significant moderating effect was observed at the distal site for Leg 1 (b = 0.03, p = 0.69) or Leg 2 (b = -0.026, p = 0.75). The results would indicate that the relationship between muscle size and strength does not depend on echo intensity. Therefore, the use of echo intensity as an index of muscle quality in healthy young adults may need to be reconsidered.

Skeletal muscle size distribution in large-sized male and female athletes.

OBJECTIVE: In healthy adults, it is generally accepted that women have less upper body muscle mass compared to men. However, it is unknown whether there are sex differences in skeletal muscle distribution in highly trained large-sized athletes. Our aim was to compare the skeletal muscle size distribution between large-sized male and female athletes. METHODS: Ten female athletes (>80 kg body mass) and twenty-one male athletes (>100 kg body mass) had muscle thickness (MT) and subcutaneous adipose tissue thickness measured by ultrasound at nine sites on the anterior and posterior aspects of the body. Total muscle mass (SM) was estimated from an ultrasound-derived prediction equation. Body fat percentage and fat-free mass were calculated from ultrasound measured subcutaneous fat thickness. RESULTS: The average SM in female athletes (30.0 kg) was approximately 70% of the mean value of the male athletes (45.3 kg).With respect to MT, the relative values of femaleto male athletes were 68% to 78% in the upper body and 85% to 92% in the lower body. Similar results were observed when analyzing data for male and female athletes (n = 5 each) who were pair matched for height. CONCLUSION: The relative values of MT for female/male athletes were higher in the lower body compared to the upper body. This is similar to that observed in healthy non-athletes indicating that this difference is not due to resistance training. The lower muscle mass in the arms and trunk of females appears to be a true sex difference but the cause of this difference is unknown.

Does Performance-Related Information Augment the Maximal Isometric Force in the Elbow Flexors?

The effects of different feedback conditions on the elbow flexors maximal voluntary isometric (MVIC) force were examined. In a single visit, twenty participants (10 males) were exposed to four conditions including, Visual only; (i.e., knowledge of results [VI]); Verbal encouragement (i.e., verbally stating pull, pull [VE]); VI and VE (VIVE); and no VI or VE (NOVIVE). Three, 5-s MVIC trials were completed for each condition. Separate 2 × 4 (sex × condition) repeated measures analyses of variance (ANOVA) were used to examine MVIC force, rate of force development (RFD200), and rate of electromyography (EMG) rise (RER200) for the 0-200-ms window. There was a significant main condition effect for MVIC force (p < 0.001). Significantly greater MVIC force was shown for VIVE compared to VE (p < 0.001) and NOVIVE (p = 0.002) conditions, and VI compared to VE (p = 0.011) and NOVIVE (p = 0.009) conditions. A significant sex × condition interaction (p = 0.036) was observed for RFD200, with significantly (p = 0.003) greater RFD200 in males compared to females, in the VI condition only. There were no significant differences in RFD200 among condition for males (p = 0.033) or females (p = 0.194). There was a significant main effect for sex (p = 0.006) for RER200, with significantly greater (p = 0.003) RER200 (conditions merged) in males (mean ± standard deviation (SD): 422.99 ± 124.67%), compared to females (220.68 ± 134.01%). Here we suggest the importance of providing VI feedback alone, or in conjunction with VE, for the measurement of elbow flexion MVIC. Additionally, these results provide a foundational framework for future studies aiming to improve feedback modalities during training or rehabilitation.

Human umbilical cord blood-derived mesenchymal stem cell implantation for osteoarthritis of the knee.

INTRODUCTION: This study aimed to investigate the clinical outcomes after human umbilical cord blood-derived mesenchymal stem cell (hUCB-MSC) implantation for medial compartment (MC) osteoarthritis of the knee. MATERIALS AND METHODS: Inclusion criteria were patients older than 60 years, with a kissing lesion of the MC, a full-thickness chondral defect ≥ 4 cm2 of the medial femoral condyle (MFC), and a varus deformity ≥ 3° on a long cassette scanogram. The mean age was 64.9 ± 4.4 years and the mean chondral defect of the MFC was 7.2 ± 1.9 cm2. A mixture of sodium hyaluronate and hUCB-MSC was implanted into the chondral defect and a high tibial osteotomy was performed in all patients. International Knee Documentation Committee (IKDC), visual analog scale (VAS), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores were evaluated preoperatively and 1 year and 2 years postoperatively. Cartilage regeneration was evaluated in 14 (56%) patients by second-look arthroscopy at 1 year postoperatively. RESULTS: Twenty-five patients underwent hUBC-MSC implantation. IKDC, VAS, and WOMAC scores at 1 year and 2 years improved significantly compared to preoperative scores. These scores at 1 year and 2 years were not significantly different between the body mass index (BMI) < 25 group and BMI ≥ 25 group. However, the < 65-year-old group showed superior IKDC scores at 1 year and 2 years and VAS score at 2 years than the ≥ 65-year-old group. Younger age and larger size of the chondral defect were associated with a significantly greater improvement in IKDC, VAS and WOMAC scores at 2 years. Second-look arthroscopy demonstrated International Cartilage Repair Society-Cartilage Repair Assessment grade I in six (42.9%) patients and grade II in eight (57.1%). CONCLUSIONS: hUCB-MSC implantation regenerated cartilage satisfactorily and showed satisfactory clinical outcomes in patients older than 60 years who had MC osteoarthritis.

Cross-Education of Muscular Endurance: A Scoping Review.

BACKGROUND: It is well established that performing unilateral resistance training can increase muscle strength not only in the trained limb but also in the contralateral untrained limb, which is widely known as the cross-education of strength. However, less attention has been paid to the question of whether performing unilateral resistance training can induce cross-education of muscular endurance, despite its significant role in both athletic performance and activities of daily living. OBJECTIVES: The objectives of this scoping review were to provide an overview of the existing literature on cross-education of muscular endurance, as well as discuss its potential underlying mechanisms and offer considerations for future research. METHODS: A scoping review was conducted on the effects of unilateral resistance training on changes in muscular endurance in the contralateral untrained limb. This scoping review was conducted in PubMed, SPORTDiscus, and Scopus. RESULTS: A total of 2000 articles were screened and 21 articles met the inclusion criteria. Among the 21 included studies, eight studies examined the cross-education of endurance via absolute (n = 6) or relative (n = 2) muscular endurance test, while five studies did not clearly indicate whether they examined absolute or relative muscular endurance. The remaining eight studies examined different types of muscular endurance measurements (e.g., time to task failure, total work, and fatigue index). CONCLUSION: The current body of the literature does not provide sufficient evidence to draw clear conclusions on whether the cross-education of muscular endurance is present. The cross-education of muscular endurance (if it exists) may be potentially driven by neural adaptations (via bilateral access and/or cross-activation models that lead to cross-education of strength) and increased tolerance to exercise-induced discomfort. However, the limited number of available randomized controlled trials and the lack of understanding of underlying mechanisms provide a rationale for future research.

The Plateau in Muscle Growth with Resistance Training: An Exploration of Possible Mechanisms.

It is hypothesized that there is likely a finite ability for muscular adaptation. While it is difficult to distinguish between a true plateau following a long-term training period and short-term stalling in muscle growth, a plateau in muscle growth has been attributed to reaching a genetic potential, with limited discussion on what might physiologically contribute to this muscle growth plateau. The present paper explores potential physiological factors that may drive the decline in muscle growth after prolonged resistance training. Overall, with chronic training, the anabolic signaling pathways may become more refractory to loading. While measures of anabolic markers may have some predictive capabilities regarding muscle growth adaptation, they do not always demonstrate a clear connection. Catabolic processes may also constrain the ability to achieve further muscle growth, which is influenced by energy balance. Although speculative, muscle cells may also possess cell scaling mechanisms that sense and regulate their own size, along with molecular brakes that hinder growth rate over time. When considering muscle growth over the lifespan, there comes a point when the anabolic response is attenuated by aging, regardless of whether or not individuals approach their muscle growth potential. Our goal is that the current review opens avenues for future experimental studies to further elucidate potential mechanisms to explain why muscle growth may plateau.

Blood flow restriction pressure for narrow cuffs (5 cm) cannot be estimated with precision.

Blood flow restriction pressures are set relative to the lowest pressure needed to occlude blood flow with that specific cuff. Due to pressure limitations of some devices, it is often not possible to occlude blood flow in all subjects and apply a known relative pressure in the lower body with a 5 cm wide cuff.Objective. To use a device capable of generating high pressures (up to 907 mmHg) to create and validate an estimation equation for the 5 cm cuff in the lower body using a 12 cm cuff.Approach. 170 participants had their arterial occlusion pressure (AOP) with a 5 cm and 12 cm cuff and their thigh circumference measured in their right leg. The sample was randomly allocated to a prediction group (66%) and validation group (33%). Thigh circumference and 12 cm AOP were used as predictors. A Bland-Altman plot was constructed to assess agreement between measured and predicted values.Main results. The mean difference (95% confidence interval) between the observed (336.8 mmHg) and the predicted (343.9 mmHg) 5 cm AOP was 7.1 (-11.9, 26.1) mmHg. The 95% limits of agreement were -133.6 to 147.8 mmHg. There was a negative relationship between the difference and the average of predicted and measured 5 cm AOP (B= -0.317,p= 0.000043).Significance. Although this was the first study to quantify AOP over 600 mmHg with a 5 cm cuff, our equation is not valid across all levels of pressure. If possible, larger cuff widths should be employed in the lower body.

Unilateral high-load resistance training influences strength changes in the contralateral arm undergoing low-load training.

OBJECTIVES: Within-subject training models have become common within the exercise literature. However, it is currently unknown if training one arm with a high load would impact muscle size and strength of the opposing arm training with a low load. DESIGN: Parallel group. METHODS: 116 participants were randomized to one of three groups that completed 6-weeks (18 sessions) of elbow flexion exercise. Group 1 trained their dominant arm only, beginning with a one-repetition maximum test (≤5 attempts), followed by four sets of exercise using a weight equivalent to 8-12 repetition maximum. Group 2 completed the same training as Group 1 in their dominant arm, while the non-dominant arm completed four sets of low-load exercise (30-40 repetition maximum). Group 3 trained their non-dominant arm only, performing the same low-load exercise as Group 2. Participants were compared for changes in muscle thickness and elbow flexion one-repetition maximum. RESULTS: The greatest changes in non-dominant strength were present in Groups 1 (Δ 1.5 kg; untrained arm) and 2 (Δ1.1 kg; low-load arm with high load on opposite arm), compared to Group 3 (Δ 0.3 kg; low-load only). Only the arms being directly trained observed changes in muscle thickness (≈Δ 0.25 cm depending on site). CONCLUSIONS: Within-subject training models are potentially problematic when investigating changes in strength (though not muscle growth). This is based on the finding that the untrained limb of Group 1 saw similar changes in strength as the non-dominant limb of Group 2 which were both greater than the low-load training limb of Group 3.

Can we improve exercise-induced hypoalgesia with exercise training? An overview and suggestions for future studies.

Exercise-induced hypoalgesia refers to a reduction in pain sensitivity following a single bout of exercise, which has been shown to be diminished or impaired with aging and chronic pain. Exercise training (repeated bouts of exercise over time) is often recommended as a non-pharmacological treatment for chronic pain and age-related functional declines. However, whether exercise training can augment the exercise-induced hypoalgesia has not been well studied. The purpose of this paper is to 1) provide an overview of the existing literature investigating the effect of exercise training on the magnitude of exercise-induced hypoalgesia, and 2) discuss potential underlying mechanisms as well as considerations for future research. Given the paucity of randomized controlled trials in this area, the effects of exercise training on exercise-induced hypoalgesia are still unclear. Several potential mechanisms have been proposed to explain the impaired exercise-induced hypoalgesia in chronic pain and older individuals (e.g., endogenous opioid, cardiovascular, and immune system). Exercise training appears to induce physiological changes in those systems, however, further investigations are necessary to test whether this will lead to improved exercise-induced hypoalgesia. Future research should consider including a time- and age-matched non-training group and utilizing the same exercise protocol for testing exercise-induced hypoalgesia across intervention groups.