The influence of sex, hemoglobin mass, and skeletal muscle characteristics on cycling critical power.

Critical power (CP) represents an important threshold for exercise performance and fatiguability. We sought to determine the extent to which sex, hemoglobin mass (Hbmass), and skeletal muscle characteristics influence CP. Before CP determination (i.e., 3-5 constant work rate trials to task failure), Hbmass and skeletal muscle oxidative capacity (τ) were measured and vastus lateralis (VL) muscle biopsy samples were collected from 12 females and 12 males matched for aerobic fitness relative to fat-free mass (FFM) [means (SD); V̇o2max: 59.2 (7.7) vs. 59.5 (7.1) mL·kg·FFM-1·min-1, respectively]. Males had a significantly greater CP than females in absolute units [225 (28) vs. 170 (43) W; P = 0.001] but not relative to body mass [3.0 (0.6) vs. 2.7 (0.6) W·kg·BM-1; P = 0.267] or FFM [3.6 (0.7) vs. 3.7 (0.8) W·kg·FFM-1; P = 0.622]. Males had significantly greater W' (P ≤ 0.030) and greater Hbmass (P ≤ 0.016) than females, regardless of the normalization approach; however, there were no differences in mitochondrial protein content (P = 0.375), τ (P = 0.603), or MHC I proportionality (P = 0.574) between males and females. Whether it was expressed in absolute or relative units, CP was positively correlated with Hbmass (0.444 ≤ r ≤ 0.695; P < 0.05), mitochondrial protein content (0.413 ≤ r ≤ 0.708; P < 0.05), and MHC I proportionality (0.506 ≤ r ≤ 0.585; P < 0.05), and negatively correlated with τ when expressed in relative units only (-0.588 ≤ r ≤ -0.527; P < 0.05). Overall, CP was independent of sex, but variability in CP was related to Hbmass and skeletal muscle characteristics. The extent to which manipulations in these physiological parameters influence CP warrants further investigation to better understand the factors underpinning CP.NEW & NOTEWORTHY In males and females matched for aerobic fitness [maximal oxygen uptake normalized to fat-free mass (FFM)], absolute critical power (CP) was greater in males, but relative CP (per kilogram body mass or FFM) was similar between sexes. CP correlated with hemoglobin mass, mitochondrial protein content, myosin heavy chain type I proportion, and skeletal muscle oxidative capacity. These findings demonstrate the importance of matching sexes for aerobic fitness, but further experiments are needed to determine causality.

Contraction intensity affects NIRS-derived skeletal muscle oxidative capacity but not its relationships to mitochondrial protein content or aerobic fitness.

To further refine the near-infrared spectroscopy (NIRS)-derived measure of skeletal muscle oxidative capacity in humans, we sought to determine whether the exercise stimulus intensity affected the τ value and/or influenced the magnitude of correlations with in vitro measures of mitochondrial content and in vivo indices of exercise performance. Males (n = 12) and females (n = 12), matched for maximal aerobic fitness per fat-free mass, completed NIRS-derived skeletal muscle oxidative capacity tests for the vastus lateralis following repeated contractions at 40% (τ40) and 100% (τ100) of maximum voluntary contraction, underwent a skeletal muscle biopsy of the same muscle, and performed multiple intermittent isometric knee extension tests to task failure to establish critical torque (CT). The value of τ100 (34.4 ± 7.0 s) was greater than τ40 (24.2 ± 6.9 s, P < 0.001), but the values were correlated (r = 0.688; P < 0.001). The values of τ40 (r = -0.692, P < 0.001) and τ100 (r = -0.488, P = 0.016) correlated with myosin heavy chain I percentage and several markers of mitochondrial content, including COX II protein content in whole muscle (τ40: r = -0.547, P = 0.006; τ100: r = -0.466, P = 0.022), type I pooled fibers (τ40: r = -0.547, P = 0.006; τ100: r = -0.547, P = 0.006), and type II pooled fibers (τ40: r = -0.516, P = 0.009; τ100: r = -0.635, P = 0.001). The value of τ40 (r = -0.702, P < 0.001), but not τ100 (r = -0.378, P = 0.083) correlated with critical torque (CT); however, neither value correlated with W' (τ40: r = 0.071, P = 0.753; τ100: r = 0.054, P = 0.812). Overall, the NIRS method of assessing skeletal muscle oxidative capacity is sensitive to the intensity of skeletal muscle contraction but maintains relationships to whole body fitness, isolated limb critical intensity, and mitochondrial content regardless of intensity.NEW & NOTEWORTHY Skeletal muscle oxidative capacity measured using near-infrared spectroscopy (NIRS) was lower following high-intensity compared with low-intensity isometric knee extension contractions. At both intensities, skeletal muscle oxidative capacity was correlated with protein markers of mitochondrial content (in whole muscle and pooled type I and type II muscle fibers) and critical torque. These findings highlight the importance of standardizing contraction intensity while using the NIRS method with isometric contractions and further demonstrate its validity.

The influence of skeletal muscle mitochondria and sex on critical torque and performance fatiguability in humans.

Critical torque (CT) represents the highest oxidative steady state for intermittent knee extensor exercise, but the extent to which it is influenced by skeletal muscle mitochondria and sex is unclear. Vastus lateralis muscle biopsy samples were collected from 12 females and 12 males -matched for relative maximal oxygen uptake normalized to fat-free mass (FFM) (F: 57.3 (7.5) ml (kg FFM)-1  min-1 ; M: 56.8 (7.6) ml (kg FFM)-1  min-1 ; P = 0.856) - prior to CT determination and performance fatiguability trials. Males had a lower proportion of myosin heavy chain (MHC) I isoform (40.6 (18.4)%) compared to females (59.5 (18.9)%; P = 0.021), but MHC IIa and IIx isoform distributions and protein markers of mitochondrial content were not different between sexes (P > 0.05). When normalized to maximum voluntary contraction (MVC), the relative CT (F: 42.9 (8.3)%; M: 37.9 (9.0)%; P = 0.172) and curvature constant, W' (F: 26.6 (11.0) N m s (N m)-1 ; M: 26.4 (6.5) N m s (N m)-1 ; P = 0.962) were not significantly different between sexes. All protein biomarkers of skeletal muscle mitochondrial content, as well as the proportion of MHC I isoform, positively correlated with relative CT (0.48 < r < 0.70; P < 0.05), and the proportion of MHC IIx isoform correlated positively with relative W' (r = 0.57; P = 0.007). Indices of performance fatiguability were not different between males and females for MVC- and CT-controlled trials (P > 0.05). Greater mitochondrial protein abundance was associated with attenuated declines in potentiated twitch torque for exercise at 60% MVC (P < 0.05); however, the influence of mitochondrial protein abundance on performance fatiguability was reduced when exercise was prescribed relative to CT. Whether these findings translate to whole-body exercise requires additional research. KEY POINTS: The quadriceps critical torque represents the highest intensity of intermittent knee extensor exercise for which an oxidative steady state is attainable, but its relationship with skeletal muscle mitochondrial protein abundance is unknown. Matching males and females for maximal oxygen uptake relative to fat-free mass facilitates investigations of sex differences in exercise physiology, but studies that have compared critical torque and performance fatiguability during intermittent knee extensor exercise have not ensured equal aerobic fitness between sexes. Skeletal muscle mitochondrial protein abundance was correlated with critical torque and fatigue resistance for exercise prescribed relative to maximum voluntary contraction but not for exercise performed relative to the critical torque. Differences between sexes in critical torque, skeletal muscle mitochondrial protein abundance and performance fatiguability were not statistically significant. Our results suggest that skeletal muscle mitochondrial protein abundance may contribute to fatigue resistance by influencing the critical intensity of exercise.

Time course and fibre type-dependent nature of calcium-handling protein responses to sprint interval exercise in human skeletal muscle.

Sprint interval training (SIT) causes fragmentation of the skeletal muscle sarcoplasmic reticulum Ca2+ release channel, ryanodine receptor 1 (RyR1), 24 h post-exercise, potentially signalling mitochondrial biogenesis by increasing cytosolic [Ca2+ ]. Yet, the time course and skeletal muscle fibre type-specific patterns of RyR1 fragmentation following a session of SIT remain unknown. Ten participants (n = 4 females; n = 6 males) performed a session of SIT (6 × 30 s 'all-out' with 4.5 min rest after each sprint) with vastus lateralis muscle biopsy samples collected before and 3, 6 and 24 h after exercise. In whole muscle, full-length RyR1 protein content was significantly reduced 6 h (mean (SD); -38 (38)%; P < 0.05) and 24 h post-SIT (-30 (48)%; P < 0.05) compared to pre-exercise. Examining each participant's largest response in pooled samples, full-length RyR1 protein content was reduced in type II (-26 (30)%; P < 0.05) but not type I fibres (-11 (40)%; P > 0.05). Three hours post-SIT, there was also a decrease in sarco(endo)plasmic reticulum Ca2+ ATPase 1 in type II fibres (-23 (17)%; P < 0.05) and sarco(endo)plasmic reticulum Ca2+ ATPase 2a in type I fibres (-19 (21)%; P < 0.05), despite no time effect for either protein in whole muscle samples (P > 0.05). PGC1A mRNA content was elevated 3 and 6 h post-SIT (5.3- and 3.7-fold change from pre, respectively; P < 0.05 for both), but peak PGC1A mRNA expression was not significantly correlated with peak RyR1 fragmentation (r2  = 0.10; P > 0.05). In summary, altered Ca2+ -handling protein expression, which occurs primarily in type II muscle fibres, may influence signals for mitochondrial biogenesis as early as 3-6 h post-SIT in humans. KEY POINTS: Sprint interval training (SIT) has been shown to cause fragmentation of the sarcoplasmic reticulum calcium-release channel, ryanodine receptor 1 (RyR1), 24 h post-exercise, which may act as a signal for mitochondrial biogenesis. In this study, the time course was examined of RyR1 fragmentation in human whole muscle and pooled type I and type II skeletal muscle fibres following a single session of SIT. Full-length RyR1 protein content was significantly lower than pre-exercise by 6 h post-SIT in whole muscle, and fragmentation was detectable in type II but not type I fibres, though to a lesser extent than in whole muscle. The peak in PGC1A mRNA expression occurred earlier than RyR1 fragmentation. The increased temporal resolution and fibre type-specific responses for RyR1 fragmentation provide insights into its importance to mitochondrial biogenesis in humans.

Exploring the Business Case for Improving Quality of Care for Patients With Chronic Rotator Cuff Tears.

BACKGROUND AND OBJECTIVES: Currently, management of patients presenting with chronic rotator cuff tears in Alberta is in need of quality improvements. This article explores the potential impact of a proposed care pathway whereby all patients presenting with chronic rotator cuff tears in Alberta would adopt an early, conservative management plan as the first stage of care; ultrasound investigation would be the preferred tool for diagnosing a rotator cuff tear; and only patients are referred for surgery once conservative measures have been exhausted. METHODS: We evaluate evidence in support of surgery and conservative management, compare care in the current state with the proposed care pathway, and identify potential solutions in moving toward optimal care. RESULTS: A literature search resulted in an absence of indications for either surgical or conservative management. Conservative management has the potential to reduce utilization of public health care resources and may be preferable to surgery. The proposed care pathway has the potential to avoid nearly Can $87 000 in public health care costs in the current system for every 100 patients treated successfully with conservative management. CONCLUSION: The proposed care pathway is a low-cost, first-stage treatment that is cost-effective and has the potential to reduce unnecessary, costly surgical procedures.

Further validation and reliability testing of the Rotator Cuff Quality of Life Index (RC-QOL) according to the Consensus-Based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines.

BACKGROUND: The Rotator Cuff Quality of Life Index (RC-QOL) was developed to evaluate quality of life in patients with rotator cuff disorders (RCD). The purpose of this study was to provide additional reliability, validity, and responsiveness testing in accordance with the Consensus-Based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines. METHODS: Preliminary patient interviews included 15 patients. Seventy patients (mean age, 58; standard deviation, 9 years) with RCD were evaluated. Methodology testing included internal consistency, test-retest reliability, measurement error, content validity, and construct validity. Responsiveness, interpretability, and generalizability were also analyzed. RESULTS: The Cronbach α was 0.96 (95% confidence interval, 0.89-0.99; range, 0.72-0.94). The intraclass correlation coefficient for the RC-QOL was 0.87 (95% confidence interval, 0.79-0.85; range, 0.77-0.88). The standard error of measurement was 8 (range, 7-13). The smallest detectable change was 3 (range, 2-4). Content validity was confirmed through standardized patient interviews. All a priori hypotheses were confirmed. No floor or ceiling effects were present. The minimally clinical important difference ranged between 7 and 14 points. The study met the COSMIN criteria for interpretability and generalizability. CONCLUSION: The RC-QOL is a reliable and valid measure of health-related quality of life in patients with chronic RCD. The results of this study added to the methodologic quality assessment of the RC-QOL, completing 7 of 10 COSMIN criteria.

Using the modified Delphi method to establish clinical consensus for the diagnosis and treatment of patients with rotator cuff pathology.

BACKGROUND: Patients presenting to the healthcare system with rotator cuff pathology do not always receive high quality care. High quality care occurs when a patient receives care that is accessible, appropriate, acceptable, effective, efficient, and safe. The aim of this study was twofold: 1) to develop a clinical pathway algorithm that sets forth a stepwise process for making decisions about the diagnosis and treatment of rotator cuff pathology presenting to primary, secondary, and tertiary healthcare settings; and 2) to establish clinical practice guidelines for the diagnosis and treatment of rotator cuff pathology to inform decision-making processes within the algorithm. METHODS: A three-step modified Delphi method was used to establish consensus. Fourteen experts representing athletic therapy, physiotherapy, sport medicine, and orthopaedic surgery were invited to participate as the expert panel. In round 1, 123 best practice statements were distributed to the panel. Panel members were asked to mark "agree" or "disagree" beside each statement, and provide comments. The same voting method was again used for round 2. Round 3 consisted of a final face-to-face meeting. RESULTS: In round 1, statements were grouped and reduced to 44 statements that met consensus. In round 2, five statements reached consensus. In round 3, ten statements reached consensus. Consensus was reached for 59 statements representing five domains: screening, diagnosis, physical examination, investigations, and treatment. The final face-to-face meeting was also used to develop clinical pathway algorithms (i.e., clinical care pathways) for three types of rotator cuff pathology: acute, chronic, and acute-on-chronic. CONCLUSION: This consensus guideline will help to standardize care, provide guidance on the diagnosis and treatment of rotator cuff pathology, and assist in clinical decision-making for all healthcare professionals.

The rotator cuff quality-of-life index predicts the outcome of nonoperative treatment of patients with a chronic rotator cuff tear.

BACKGROUND: Chronic rotator cuff tears are prevalent and can be disabling. The existing literature is unclear regarding the effectiveness of nonoperative treatment. The purposes of this study were to determine whether the outcome of nonoperative treatment can be predicted on the basis of the presenting clinical characteristics and whether the outcome achieved at three months after treatment can be maintained at two years. METHODS: The prospective cohort included ninety-three patients with a documented chronic full-thickness rotator cuff tear. Patients underwent a three-month supervised program of nonoperative treatment and were then evaluated by an orthopaedic surgeon. The treatment outcome was defined as a success if surgical treatment was no longer deemed appropriate by both patient and surgeon because the patient had improved considerably and was predominantly asymptomatic. The outcome was defined as a failure if the patient elected to have surgery after failing to improve and remaining symptomatic. The presenting clinical characteristics that were analyzed included age, sex, smoking status, hand dominance, duration of symptoms, onset (traumatic etiology or insidious onset), shoulder motion, external rotation strength, tear size as documented by ultrasonography or magnetic resonance imaging, and the Rotator Cuff Quality-of-Life Index (RC-QOL). RESULTS: Seventy (75%) of the patients were successfully treated. Logistic regression analysis showed that the baseline RC-QOL score was a significant predictor of outcome (p = 0.017). Eighty-nine percent of patients maintained their three-month outcome at two years of follow-up. CONCLUSIONS: The RC-QOL was predictive of the outcome of nonoperative treatment of patients with a chronic full-thickness rotator cuff tear. Patients in whom the nonoperative treatment was deemed successful at the conclusion of three months of treatment had a very high chance of ongoing success at two years after the initiation of treatment.