Quadriceps Muscle Volume Research Articles

The relationship between Quadriceps muscle volume and patellar cartilage morphology in patients with knee osteoarthritis

The purpose of this study was to determine whether quadriceps strength and whole muscle volume or distal vastii muscle volumes are associated with Magnetic Resonance Imaging-derived measures of patellar cartilage morphology in patients with knee Osteoarthritis.

Association between individual quadriceps muscle volume/enthesis and patello femoral joint cartilage morphology

IntroductionThe aim of this study was to determine the association between individual quadriceps muscle volumes and the quadriceps enthesis structures and cartilage morphology at the patellofemoral joint (PFJ).MethodsWe studied 12 cadavers (age 75 ± 5 years). For both legs, individual quadriceps muscles (vastus lateralis (VL), rectus femoris (RF), vastus intermedialis (VI) and vastus medialis (VM)) were dissected and their volumes measured. Cartilage areas at the PFJ were classified using the International Cartilage Repair Society (ICRS) score. Histological sections were evaluated at the quadriceps tendon enthesis (laterally, centrally and medially). Several variables were calculated on the binary images based on two-dimensional analysis. These were apparent bone area (BA) and apparent trabecular thickness (TH). A Spearman rank test was used to determine the strength of correlation between individual quadriceps muscles volume, the structure of the quadriceps tendon enthesis and the ICRS score.ResultsThe thickness of calcified fibrocartilage tissue was significantly greater in the central part of the enthesis than both medially (P = 0.03) and laterally (P = 0.04). Uncalcified fibrocartilage was significantly thicker laterally (P = 0.04) and centrally (P = 0.02) than medially. Muscle volume was highest (P <0.05) for the VL, followed by the VI, VM and RF. There was no association between total and individual muscle volumes and ICRS or BA. However, there was a strong positive correlation (r = 0.81) between the VL/VM volume ratio and BA ratio (bone volume at the lateral part divided by bone volume at the medial part). There was a moderate positive correlation between VL/VM and ICRS (r = 0.65) and between ICRS and BA ratio (lateral/medial; r = 0.74).ConclusionsIndividual and total quadriceps volumes were not correlated with cartilage loss at the PFJ or fibrocartilage thickness. However, both VL/VM and BA ratio (lateral/medial) were positively correlated with ICRS scoring and therefore could be a tool for predicting degree of PFJ osteoarthritis severity.

Differences in Neuromuscular Control and Quadriceps Morphology Between Potential Copers and Noncopers Following Anterior Cruciate Ligament Injury

Prospective cross-sectional study. To compare knee muscle morphology and voluntary neuromuscular control in individuals who sustained an anterior cruciate ligament (ACL) injury and were identified as being capable of avoiding surgery (potential copers) and those who were recommended for surgery (noncopers), within 6 months of injury. Quadriceps atrophy and poor neuromuscular control have been found in noncopers. However, the reasons why some noncopers may be able to avoid surgery remain elusive. Twenty participants (10 ACL-deficient noncopers and 10 ACL-deficient potential copers) were included in this study. Axial spin-echo, T1-weighted magnetic resonance imaging data of the lower extremities were captured. The volume and maximum cross-sectional area (CSA) of each muscle of the quadriceps and hamstrings were calculated following digital reconstruction. In addition, voluntary neuromuscular control was evaluated using an established target-matching task that required participants to produce static isometric loads across the knee joint. Electromyography was acquired from 5 muscles as participants performed the target-matching task. Circular statistics were used to calculate a specificity index to describe how well focused each muscle was activated toward its primary direction of muscle action. The ACL-deficient limb was then compared to the uninvolved limb of the noncopers and potential copers. The vasti (vastus medialis and vastus intermedius) of the involved limb of the noncopers were significantly smaller (P<.031) in comparison to those of their uninvolved limb. The potential copers' vastus lateralis maximum CSA (P = .047), total quadriceps muscle volume (P = .020) and maximum CSA (P = .015), and quadriceps-hamstring ratio volume (P = .021) and maximum CSA (P = .007) demonstrated quadriceps atrophy. However, only the ACL-deficient limb of the older (mean ± SD age, 27.4 ± 11.4 versus 19.9 ± 3.3 years; P = .032) and lower-activity-level (3.3 ± 0.5 versus 3.6 ± 0.5; P = .098) noncoper group demonstrated reduced rectus femoris (P = .057) and lateral hamstring (P = .064) neuromuscular control in comparison to their uninvolved limb. These findings suggest that quadriceps and hamstring muscle function, rather than muscle size, may be an important factor in the varied response early after ACL injury.

Type VI collagen turnover‐related peptides—novel serological biomarkers of muscle mass and anabolic response to loading in young men

BackgroundImmobilization-induced loss of muscle mass is a complex phenomenon with several parallels to sarcopenic and cachectic muscle loss. Muscle is a large organ with a protein turnover that is orders of magnitude larger than most other tissues. Thus, we hypothesize that muscle loss and regain is reflected by peptide biomarkers derived from type VI collagen processing released in the circulation.MethodsIn order to test this hypothesis, we set out to develop an ELISA assay against an type VI collagen N-terminal globular domain epitope (IC6) and measured the levels of IC6 and an MMP-generated degradation fragment of collagen 6, (C6M) in a human immobilization–remobilization study setup with young (n = 11) and old (n = 9) men. They were subjected to 2 weeks of unilateral lower limb immobilization followed by 4 weeks of remobilization including thrice weekly resistance training, using the contralateral leg as internal controls. Subjects were sampled for strength, quadriceps muscle volume and blood at baseline (PRE), post-immobilization (2W), and post-remobilization (4W). Blood were subsequently analyzed for levels of the C6M and IC6 biomarkers. We subsequently tested if there was any correlation between C6M, IC6, or the C6M/IC6 ratio and muscle mass or strength at baseline. We also tested whether there was any relation between these biomarkers and changes in muscle mass or strength with immobilization or remobilization.ResultsThe model produced significant loss of muscle mass and strength in the immobilized leg. This loss was bigger in young subjects than in elderly, but whereas the young recovered almost fully, the elderly had limited regrowth of muscle. We found a significant correlation between IC6 and muscle mass at baseline in young subjects (R2 = 0.6563, p = 0.0045), but none in the elderly. We also found a significant correlation between C6M measured at the 4W time point and the change in muscle mass during remobilization, again only manifesting in the young men(R2 = 0.6523, p = 0.0085). This discrepancy between the young and the elderly may be caused in part by much smaller changes in muscle mass in the elderly and partly by the relative small sample size.ConclusionWhile we cannot rule out the possibility that these biomarkers in part stem from other tissues, our results strongly indicate that these markers represent novel biomarkers of muscle mass or change in muscle mass in young men.Electronic supplementary materialThe online version of this article (doi:10.1007/s13539-013-0114-x) contains supplementary material.

The individual and combined influence of ACE and ACTN3 genotypes on muscle phenotypes before and after strength training

Alternative measures of muscle size, strength, and power to those used in previous studies could help resolve the controversy surrounding associations between polymorphisms of the angiotensin-I converting enzyme (ACE) and α-actinin-3 (ACTN3) genes and skeletal muscle phenotypes, and the responses to resistance training (RT). To this end, we measured quadriceps femoris muscle volume (Vm), physiological cross-sectional area (PCSA), maximum isometric force (Ft), specific force (Ft per unit PCSA), maximum isoinertial strength (1-RM), and maximum power (Wmax ; n = 40) before and after 9-week knee extension RT in 51 previously untrained young men, who were genotyped for the ACE I/D and ACTN3 R577X polymorphisms. ACTN3 R-allele carriers had greater Vm, 1-RM, and Wmax than XX homozygotes at baseline (all P < 0.05), but responses to RT were independent of ACTN3 genotype (all P > 0.05). Muscle phenotypes were independent of ACE genotype before (all P > 0.05) and after RT (all P > 0.01). However, people with the "optimal" ACE+ACTN3 genotype combination had greater baseline 1-RM and Wmax compared to those with the "suboptimal" profile (both P < 0.0125). We show for the first time that the ACTN3 R577X polymorphism is associated with human Vm and (independently and in combination with the ACE I/D polymorphism) influences 1-RM and Wmax.

Relationship of intermuscular fat volume in the thigh with knee extensor strength and physical performance in women at risk of or with knee osteoarthritis

To determine the extent to which thigh intermuscular fat (IMF) and quadriceps muscle (QM) volumes explained variance in knee extensor strength and physical performance in women with radiographic knee osteoarthritis (ROA) and without. Baseline data from 125 women (age ≥50 years) in the Osteoarthritis Initiative study, with or at risk of knee ROA were included. Knee extensor strength was measured using a fixed force transducer, normalized to body mass (N/kg). Physical performance was the time required for 5 repeated chair stands (seconds). The IMF and QM volumes, normalized to height (cm(3) /meter), were yielded from analyses of T1-weighted axial magnetic resonance images of the midthigh. Mean IMF and QM volumes, extensor strength, and physical performance were compared between women with and without ROA, controlling for age. Hierarchical multiple regressions determined whether IMF and QM volumes were related to strength and performance after controlling for age, ROA status (yes/no), alignment, and pain. Compared to subjects with ROA, the subjects without ROA were stronger and performed chair stands faster (P < 0.05). After adjusting for age, those subjects without ROA had less mean ± SD IMF (61.1 ± 20.3 cm(3) /meter) compared to mean ± SD ROA (72.0 ± 25.0 cm(3) /meter; P < 0.05). In the entire sample, 21.1% of variance in knee extensor strength was explained by alignment, pain, and IMF. A model explaining 13.4% of variance in physical performance included OA status and IMF. QM volume was unrelated to strength and physical performance. IMF volume explained a small amount of variance in knee extensor strength and physical performance among women with or at risk of knee ROA.

The Potential Role of Dietary Intake in Explaining Postoperative Muscle Loss in Total Knee Arthoplasty (TKA)

Post-operative muscle loss has been identified as the greatest contributor to osteoarthritis patients’ long-term strength deficits, explaining 77% of muscle weakness one to three years after total knee arthroplasty (TKA) for the treatment of osteoarthritis in the knee. Essential amino acid supplementation may help reduce atrophy, but other factors could have an equally influential role. Patients’ food intake could likewise affect atrophy, and thus dietary intake must be measured in order to determine whether essential amino acids reduce muscle loss following TKA. Subjects with a minimal dietary intake could exacerbate muscle loss because fasting causes the body to break down skeletal muscle protein to liberate amino acids for use as gluconeogenic precursors in the liver. As a result, individuals with different diets may experience differing degrees of muscle atrophy. This investigation seeks to test the hypothesis that higher rates of muscle atrophy in subject groups could be explained by comparatively poorer dietary intake. For this study, subjects completed a total of three 24-hour food logs before surgery, then two, and six weeks post-TKA. During these periods, bilateral quadriceps muscle volume was determined using magnetic resonance imaging (MRI). Baseline and six-week whole-body dual-energy X-ray (DEXA) scans were also performed to compare changes in lean tissue and fat mass. Data collected indicated there was no significant difference in dietary intake between the control group and treatment group, suggesting that any muscle saved in the treatment group was a result of essential amino acid supplementation.

Aerobic exercise training induces skeletal muscle hypertrophy and age-dependent adaptations in myofiber function in young and older men

To examine potential age-specific adaptations in skeletal muscle size and myofiber contractile physiology in response to aerobic exercise, seven young (YM; 20 ± 1 yr) and six older men (OM; 74 ± 3 yr) performed 12 wk of cycle ergometer training. Muscle biopsies were obtained from the vastus lateralis to determine size and contractile properties of isolated slow [myosin heavy chain (MHC) I] and fast (MHC IIa) myofibers, MHC composition, and muscle protein concentration. Aerobic capacity was higher (P < 0.05) after training in both YM (16 ± 2%) and OM (13 ± 3%). Quadriceps muscle volume, determined via MRI, was 5 ± 1 and 6 ± 1% greater (P < 0.05) after training for YM and OM, respectively, which was associated with an increase in MHC I myofiber cross-sectional area (CSA), independent of age. MHC I peak power was higher (P < 0.05) after training for both YM and OM, while MHC IIa peak power was increased (P < 0.05) with training in OM only. MHC I and MHC IIa myofiber peak and normalized (peak force/CSA) force were preserved with training in OM, while MHC I peak force/CSA and MHC IIa peak force were lower (P < 0.05) after training in YM. The age-dependent adaptations in myofiber function were not due to changes in protein content, as total muscle protein and myofibrillar protein concentration were unchanged (P > 0.05) with training. Training reduced (P < 0.05) the proportion of MHC IIx isoform, independent of age, whereas no other changes in MHC composition were observed. These data suggest relative improvements in muscle size and aerobic capacity are similar between YM and OM, while adaptations in myofiber contractile function showed a general improvement in OM. Training-related increases in MHC I and MHC IIa peak power reveal that skeletal muscle of OM is responsive to aerobic exercise training and further support the use of aerobic exercise for improving cardiovascular and skeletal muscle health in older individuals.

Quadriceps volumes are reduced in people with patellofemoral joint osteoarthritis

This study aimed to (1) compare the volumes of vastus medialis (VM), vastus lateralis (VL), vastus intermedius and rectus femoris and the ratio of VM/VL volumes between asymptomatic controls and patellofemoral joint osteoarthritis (PFJ OA) participants; and (2) assess the relationships between cross-sectional area (CSA) and volumes of the VM and VL in individuals with and without PFJ OA. Twenty-two participants with PFJ OA and 11 controls aged ≥ 40 years were recruited from the community and practitioner referrals. Muscle volumes of individual quadriceps components were measured from thigh magnetic resonance (MR) images. The CSA of the VM and lateralis were measured at 10 equally distributed levels (femoral condyles to lesser femoral trochanter). PFJ OA individuals had smaller normalized VM (mean difference 0.90 cm(3) · kg(-1), α = 0.011), VL (1.50 cm(3) · kg(-1), α = 0.012) and rectus femoris (0.71 cm(3) · kg(-1), α = 0.009) volumes than controls. No differences in the VM/VL ratio were observed. The CSA at the third level (controls) and fourth level (PFJ OA) above the femoral condyles best predicted VM volume, whereas the VL volume was best predicted by the CSA at the seventh level (controls) and sixth level (PFJ OA) above the femoral condyles. Reduced quadriceps muscle volume was a feature of PFJ OA. Muscle volume could be predicted from CSA measurements at specific levels in PFJ OA patients and controls.

The effect of flywheel-based resistive exercise workouts on testosterone/cortisol ratios

Toassessthesubsequent testosterone/cortisol ratio(TCr)fromflywheel-basedresistiveexercise, usingawithin-subjects design volunteers (7men, 10 women) performed three seated legpress workouts on an ergometer (YoYoTechnologies, Stockholm Sweden). Comprised of ten-repetition sets, the workouts entailed: a three-set protocol composed of concentric and eccentric actions (CE3), as well as concentric-only paradigms of three (CO3) and six (CO6) sets. Venous blood, collected before bouts and at one and 30 minutes post-exercise, was used to quantify the TCr. Data were examined with ANOVA and multivariate regression. ANOVA yielded a gender x time TCr interaction, as male values declined significantly yet women's data were unchanged. With the TCr at one and 30 minutes post-exercise as separate criterion measures, and data pooled across genders and workouts, multivariate regression revealed significance per dependent variable. Univariate correlations showed the best predictors of the post-exercise TCr in descending order were: body mass, average power and delta lactate. Gender and quadriceps muscle volume may have acted as confounding variables to allow body mass to the best current study predictor. Continued research should examine additional predictor variables, as current results only accounted for roughly 30% of the total criterion measure variance.

The Relationship Between Spasticity and Muscle Volume of the Knee Extensors in Children With Cerebral Palsy

The purpose of this study was to examine the relationship between spasticity and muscle volume in children with cerebral palsy (CP), using isokinetic dynamometry and magnetic resonance imaging. A retrospective sample of 8 children with diplegic CP was analyzed. One set of 10 passive knee flexion movements was completed at a velocity of 180° per second with concurrent surface electromyography of the medial hamstrings (MH) and vastus lateralis (VL) to assess knee extensor spasticity. Magnetic resonance imaging was used to measure maximum cross-sectional area and muscle volume of the quadriceps femoris. The quadriceps femoris muscle volume was positively correlated with MH reflex activity, VL reflex activity, MH/VL co-contraction, and peak knee extensor passive torque (P < .05). The present findings suggest that higher levels of knee extensor muscle spasticity are associated with greater quadriceps muscle volume in children with spastic diplegic CP.

Longitudinal changes in intermuscular fat volume and quadriceps muscle volume in the thighs of women with knee osteoarthritis

To quantify rates of change in quadriceps muscle (QM) and intermuscular fat (IMF) volumes over 2 years in women in the Osteoarthritis Initiative (OAI) study and examine group differences between those with radiographic osteoarthritis (ROA) and those without ROA. The OAI database was queried for women ≥50 years of age in the incident and progression cohorts with and without ROA at baseline. Midthigh magnetic resonance imaging scans (15 contiguous slices, 5 mm slice thickness) of eligible women were randomly selected and anonymized. Image pairs were registered. QM and IMF were segmented in the 12 most proximal matching slices with the segmenter blinded to image time point. Age-adjusted differences in QM and IMF volume changes between groups were tested using analysis of covariance. Forty-one women without ROA (mean ± SD age 60.7 ± 7.6 years) and 45 women with ROA (mean ± SD age 64.5 ± 6.7 years) were included. Mean ± SD QM and IMF volume changes in the non-ROA group were -4.1 ± 11.1 cm(3) and 3.4 ± 7.1 cm(3), respectively, and -5.4 ± 13.5 cm(3) and 3.1 ± 7.4 cm(3) in the ROA group, respectively. Age-adjusted between-group differences in QM and IMF changes were not significant (P > 0.05). Two-year changes in QM and IMF volumes appear consistent with aging and do not seem to be related to OA status. Direct comparison with a control cohort without OA risk factors could confirm this. Since group assignment was based on baseline data, there may have been women in the non-ROA group who developed ROA over followup, resulting in some overlap between groups.

Muscle Changes Following Cycling and/or Electrical Stimulation in Pediatric Spinal Cord Injury

Johnston TE, Modlesky CM, Betz RR, Lauer RT. Muscle changes following cycling and/or electrical stimulation in pediatric spinal cord injury. Objective To determine the effect of cycling, electrical stimulation, or both, on thigh muscle volume and stimulated muscle strength in children with spinal cord injury (SCI). Design Randomized controlled trial. Setting Children's hospital specializing in pediatric SCI. Participants Children (N=30; ages, 5–13y) with chronic SCI. Interventions Children were randomly assigned to 1 of 3 interventions: functional electrical stimulation cycling (FESC), passive cycling (PC), and noncycling, electrically stimulated exercise (ES). Each group exercised for 1 hour, 3 times per week for 6 months at home. Main Outcome Measures Preintervention and postintervention, children underwent magnetic resonance imaging to assess muscle volume, and electrically stimulated isometric muscle strength testing with the use of a computerized dynamometer. Data were analyzed via analyses of covariance (ANCOVA) with baseline measures as covariates. Within-group changes were assessed via paired t tests. Results All 30 children completed the training. Muscle volume data were complete for 24 children (8 FESC, 8 PC, 8 ES) and stimulated strength data for 27 children (9 per group). Per ANCOVA, there were differences between groups ( P<.05) for quadriceps muscle volume and stimulated strength, with the ES group having greater changes in volume and the FESC group having greater changes in strength. Within-group analyses showed increased quadriceps volume and strength for the FESC group and increased quadriceps volume for the ES group. Conclusions Children receiving either electrically stimulated exercise experienced changes in muscle size, stimulated strength, or both. These changes may decrease their risk of cardiovascular disease, insulin resistance, glucose intolerance, and type 2 diabetes. Clinical Trials Registration Number NCT00245726.

Component characteristics of thigh muscle volume in young and older healthy men

The purpose of this study was to compare the component characteristics of thigh muscle volume in Japanese young and older men. The subjects in both young (YM, n = 15) and older (OM, n = 13) men were physically active (performed aerobic-type exercise 1-3 times per week), but none of the subjects had regularly participated in resistance training for a minimum of 3 years prior to the study. Contiguous transverse magnetic resonance imaging (1.5-T scanner) images were obtained from the thigh, and total and individual (quadriceps, hamstrings and adductors) muscle volumes were calculated by multiplying the muscle cross-sectional area (CSA) by slice thickness and the total number of slices. Muscle length and average muscle CSA (muscle volume divided by muscle length) were determined for each muscle. Maximum voluntary isometric (MVC) knee extension and flexion strength were measured, and muscle quality was defined as MVC per unit average muscle CSA (MVC/CSA). Quadriceps muscle volume and average CSA were, respectively, 20% and 16% lower (P < 0.05) in the OM than in the YM, while hamstrings and adductors muscle volumes and average CSA were similar in both groups. Knee extension and flexion MVC were lower (P < 0.05) in the OM than in the YM. Knee extensor MVC/CSA was similar in the two groups, while knee flexor MVC/CSA was lower (P < 0.05) in the OM than in the YM. Our results suggest that age-related thigh muscle volume loss is muscle specific, in that greater quadriceps muscle loss was found in the older group.

Relationship between quadriceps femoris muscle volume and muscle torque at least 18 months after anterior cruciate ligament reconstruction

The purpose of this study was to evaluate motor unit recruitment in the quadriceps femoris (QF) after anterior cruciate ligament (ACL) rupture and repair. Subjects included 24 patients at ≥ 18 months after ACL reconstruction and 22 control subjects with no history of knee injury. A series of cross-sectional magnetic resonance images were obtained to compare the QF of patients' injured side with that of their uninjured sides and that of uninjured control subjects. Muscle torque per muscle volume was calculated as isokinetic peak torque divided by QF muscle volume (cm(3)). The mean muscle torque per unit volume of the injured side of patients was not significantly different from that of the uninjured side or control subjects (one-way ANOVA) Results of the present study were contrary to the results of a previous study that evaluated patients at ≤ 12 months after ACL reconstruction. The present study found that high-threshold motor unit recruitment was restored at ≥ 18 months after ACL reconstruction. Thus, clinicians must develop techniques that increase the recruitment of high-threshold motor units in the QF from the period immediately after the injury until approximately 18 months after ACL reconstruction.

No Effect of Short-term Resistance Training-Induced Muscle Hypertrophy on Muscle Aponeurosis Area in Young Men

The aponeurosis is a very broad and thin tendinous tissue that attaches to pinnate muscle fibers. Hypertrophied muscle includes increases in muscle fiber size and pennation angle, however, it is unknown whether the morphological characteristics of muscle aponeurosis would change following short-term resistance training induced muscle hypertrophy. PURPOSE: To investigate the effects of low-intensity squat training combined with leg blood flow reduction (BFR) on morphological characteristics of deep muscle aponeurosis. METHODS: Twelve males [age, 22.5 (SD 3.4) yrs; height, 1.71 (SD 0.06) m; body weight, 64.5 (SD 9.8) kg] were allocated randomly into either a BFR training (BFR-SQ, n=6) or control training (CON-SQ, n=6), both of which trained twice daily with squat exercise at an intensity of 30% of one repetition maximal (1-RM), 6 days per week for two weeks. Muscle cross-sectional area (CSA) and muscle volume were measured by magnetic resonance imaging (MRI) at baseline (pre-training) and 3 days after the final training session (post-training). Deep aponeurosis in the vastus lateralis (VL) muscle was determined by summation of the length of the aponeurosis in each MRI slice and multiplying by the slice thickness (1.0 cm). RESULTS: Quadriceps muscle CSA (mid-thigh) and muscle volume were increased 9.9% [pre, 68.5 (SD 8.4) cm2 and post, 75.1 (SD 8.5) cm2] and 8.9% [pre, 1684 (SD 260) cm3 and post, 1831 (SD 262) cm3], respectively in the BFR-SQ group and 0.9% [pre, 74.2 (SD 9.5) cm2 and post, 74.7 (SD 8.1) cm2] and 0.6% [pre, 1829 (SD 264) cm3 and post, 1839 (SD 269) cm3], respectively in the CON-SQ group. Maximal width and length of the VL muscle aponeurosis were similar between pre-training and post-training in both BFR-SQ and CON-SQ groups and the aponeurosis area in the VL did not change after the training in either group [BFR-SQ: pre, 140.4 (SD 17.6) cm2 and post, 143.7 (SD 18.4) cm2; CON-SQ: pre, 136.2 (SD 17.7) cm2 and post, 135.9 (SD 18.7) cm2]. There were no significant correlations between changes in quadriceps muscle volume and VL aponeurosis area. CONCLUSION: Our results suggest that short-term resistance training induced muscle hypertrophy does not affect the morphological characteristics of deep muscle aponeurosis.

Does Extreme Muscle Hypertrophy Determine an Impairment of Skeletal Muscle Oxidative Metabolism?

PURPOSE: The purpose was to evaluate the effects of marked skeletal muscle hypertrophy induced by chronic resistance training on skeletal muscle oxidative function. METHODS: Eleven male resistance-trained athletes (RTA, age: 25.4±1.8 [mean±SE] years) and eleven active control subjects (CTRL) were evaluated. Quadriceps femoris muscle volume was determined by magnetic resonance imaging. During incremental cycle ergometer (CE) and one-leg knee-extension (KE) exercise we determined: pulmonary O2 uptake (V'O2); skeletal muscle (vastus lateralis) fractional O2 extraction, as estimated from concentration changes in deoxygenated hemoglobin+myoglobin (delta[deoxy(Hb+Mb)]), determined by near-infrared spectroscopy and expressed as a percentage of the maximal values obtained by a transient limb ischemia. Mitochondrial respiration was evaluated by high-resolution respirometry in permeabilized ("skinned") vastus lateralis fibers obtained by biopsy. RESULTS: Body mass and quadriceps femoris muscle mass were higher in RTA (102.6±2.2 kg and 3.14±0.13 kg, respectively) vs. CTRL (77.7±1.8 and 2.36±0.08). Peak O2 uptake (V'O2peak) was lower in RTA vs. CTRL both during CE (39.6±1.6 mL/min/kg BM vs. 45.9±0.9, respectively) and KE (49.2±2.3 mL/min/100g of quadriceps muscle mass vs. 61.4±3.3). Delta[deoxy(Hb+Mb)]peak was lower in RTA vs. CTRL both in CE (52±3% vs. 72±3) and in KE (51±3% vs. 73±4). On the other hand, rather surprisingly, maximal ADP-stimulated mitochondrial respiration was higher in RTA (56.7±7.1 pmolO2/s/mg wet weight) vs. CTRL (35.7±3.1), also after the values were normalized per citrate synthase activity. CONCLUSIONS: Peak oxidative function in vivo was impaired in RTA, also after eliminating, by the adopted KE protocol, constraints related to cardiovascular O2 delivery. This finding may appear to be in contradiction with the higher maximal ADP-stimulated mitochondrial respiration observed in isolated fibers. The main limitation to oxidative function in RTA in vivo may reside in peripheral O2 diffusion. Financial support by ASI - OSMA Contract I/007/06/0, Workpackage 1B-31-1 is acknowledged.

Effect of transcutaneous electrical muscle stimulation on muscle volume in patients with septic shock*

Intensive care unit admission is associated with muscle wasting and impaired physical function. We investigated the effect of early transcutaneous electrical muscle stimulation on quadriceps muscle volume in patients with septic shock. Randomized interventional study using a single-legged exercise design with the contralateral leg serving as a paired control. A mixed 18-bed intensive care unit at a tertiary care university hospital. Eight adult male intensive care unit patients with septic shock included within 72 hrs of diagnosis. After randomization of the quadriceps muscles, transcutaneous electrical muscle stimulation was applied on the intervention side for 7 consecutive days and for 60 mins per day. All patients underwent computed tomographic scans of both thighs immediately before and after the 7-day treatment period. The quadriceps muscle was manually delineated on the computed tomography slices, and muscle volumes were calculated after three-dimensional reconstruction. Median age and Acute Physiology and Chronic Health Evaluation II score were 67 years (interquartile range, 64-72 years) and 25 (interquartile range, 20-29), respectively. During the 7-day study period, the volume of the quadriceps muscle on the control thigh decreased by 16% (4-21%, p=.03) corresponding to a rate of 2.3% per day. The volume of the stimulated muscle decreased by 20% (3-25%, p=.04) corresponding to a rate of 2.9% per day (p=.12 for the difference in decrease). There was no difference in muscle volume between the stimulated and nonstimulated thigh at baseline (p=.10) or at day 7 (p=.12). The charge delivered to the muscle tissue per training session (0.82 [0.66-1.18] coulomb) correlated with the maximum sequential organ failure assessment score. We observed a marked decrease in quadriceps volume within the first week of intensive care for septic shock. This loss of muscle mass was unaffected by transcutaneous electrical muscle stimulation applied for 60 mins per day for 7 days.

Relationship between quadriceps femoris muscle volume and muscle torque after anterior cruciate ligament rupture

The purpose of this study was to obtain evidence to support the hypothesis that motor unit recruitment is reduced in the quadriceps femoris (QF) of patients with ACL rupture. We compared muscle torque per unit volume in the QF from injured and uninjured sides to normal subjects. If high-threshold motor unit recruitment is reduced in patients with ACL rupture, this reduction will theoretically lead to a reduction in muscle torque per unit volume compared to the control group. The subjects included 22 patients with ACL rupture and 22 subjects with no history of knee injury. To identify the muscle torque per unit volume, the isokinetic peak torque was divided by QF volume which was obtained by MRI. Tests revealed that the mean muscle torque per unit volume of the uninjured and injured sides was significantly lower than those of the control group. This study demonstrated that the values of the muscle torque per unit volume of both injured and uninjured sides of patients with ACL rupture were significantly lower than those of the control group, thereby providing indirect evidence of the hindrance of motor unit recruitment in these patients. The results of the present study also indicate that there may be bilateral QF weakness in patients with ACL rupture. Since persistent QF weakness is a significant barrier to effective rehabilitation in patients with ACL injuries, a better understanding of the underlying mechanisms will allow clinicians and scientists to develop more effective therapeutic strategies for patient rehabilitation.

Inter-individual variability in adaptation of the leg muscles following a standardised endurance training programme in young women

There is considerable inter-individual variability in adaptations to endurance training. We hypothesised that those individuals with a low local leg-muscle peak aerobic capacity (VO2peak) relative to their whole-body maximal aerobic capacity (VO2max) would experience greater muscle training adaptations compared to those with a relatively high VO2peak. 53 untrained young women completed one-leg cycling to measure VO2peak and two-leg cycling to measure VO2max. The one-leg VO2peak was expressed as a ratio of the two-leg VO2max (Ratio(1:2)). Magnetic resonance imaging was used to indicate quadriceps muscle volume. Measurements were taken before and after completion of 6 weeks of supervised endurance training. There was large inter-individual variability in the pre-training Ratio(1:2) and large variability in the magnitude of training adaptations. The pre-training Ratio(1:2) was not related to training-induced changes in VO2max (P = 0.441) but was inversely correlated with changes in one-leg VO2peak and muscle volume (P < 0.05). No relationship was found between the training-induced changes in two-leg VO2max and one-leg VO2peak (r = 0.21; P = 0.129). It is concluded that the local leg-muscle aerobic capacity and Ratio(1:2) vary from person to person and this influences the extent of muscle adaptations following standardised endurance training. These results help to explain why muscle adaptations vary between people and suggest that setting the training stimulus at a fixed percentage of VO2max might not be a good way to standardise the training stimulus to the leg muscles of different people.