Changes In Muscle Cross-sectional Area Research Articles

Assessment of passive muscle elongation using Diffusion Tensor MRI: Correlation between fiber length and diffusion coefficients.

In this study we investigated the changes in fiber length and diffusion parameters as a consequence of passive lengthening and stretching of the calf muscles. We hypothesized that changes in radial diffusivity (RD) are caused by changes in the muscle fiber cross sectional area (CSA) as a consequence of lengthening and shortening of the muscle. Diffusion Tensor MRI (DT-MRI) measurements were made twice in five healthy volunteers, with the foot in three different positions (30° plantarflexion, neutral position and 15° dorsiflexion). The muscles of the calf were manually segmented on co-registered high resolution anatomical scans, and maps of RD and axial diffusivity (AD) were reconstructed from the DT-MRI data. Fiber tractography was performed and mean fiber length was calculated for each muscle group. Significant negative correlations were found between the changes in RD and changes in fiber length in the dorsiflexed and plantarflexed positions, compared with the neutral foot position. Changes in AD did not correlate with changes in fiber length. Assuming a simple cylindrical model with constant volume for the muscle fiber, the changes in the muscle fiber CSA were calculated from the changes in fiber length. In line with our hypothesis, we observed a significant positive correlation of the CSA with the measured changes in RD. In conclusion, we showed that changes in diffusion coefficients induced by passive muscle stretching and lengthening can be explained by changes in muscle CSA, advancing the physiological interpretation of parameters derived from skeletal muscle DT-MRI.

Non–Weight-Bearing and Weight-Bearing Ultrasonography of Select Foot Muscles in Young, Asymptomatic Participants: A Descriptive and Reliability Study

ObjectiveThe primary aim of this study was to determine the reliability of diagnostic ultrasound imaging for select intrinsic foot muscles using both non–weight-bearing and weight-bearing postures. Our secondary aim was to describe the change in muscle cross-sectional area (CSA) and dorsoplantar thickness when bearing weight. MethodsAn ultrasound examination was performed with a linear ultrasound transducer operating between 9 and 12 MHz. Long-axis and short-axis ultrasound images of the abductor hallucis, flexor digitorum brevis, and quadratus plantae were obtained in both the non–weight-bearing and weight-bearing postures. Two examiners independently collected ultrasound images to allow for interexaminer and intraexaminer reliability calculation. The change in muscle CSA and dorsoplantar thickness when bearing weight was also studied. ResultsThere were 26 participants (17 female) with a mean age of 25.5 ± 3.8 years and a mean body mass index of 28.0 ± 7.8 kg/m2. Inter-examiner reliability was excellent when measuring the muscles in short axis (intraclass correlation coefficient >0.75) and fair to good in long axis (intraclass correlation coefficient >0.4). Intraexaminer reliability was excellent for the abductor hallucis and flexor digitorum brevis and ranged from fair to good to excellent for the quadratus plantae. Bearing weight did not reduce interexaminer or intraexaminer reliability. All muscles exhibited a significant increase in CSA when bearing weight. ConclusionsThis is the first report to describe weight-bearing diagnostic ultrasound of the intrinsic foot muscles. Ultrasound imaging is reliable when imaging these muscles bearing weight. Furthermore, muscle CSA increases in the weight-bearing posture.

Longitudinal Changes in Muscle Cross-Sectional Area following Different Resistance Training Programs in Resistance Trained Men.

Longitudinal Changes in Muscle Cross-Sectional Area following Different Resistance Training Programs in Resistance Trained Men.

Time Course of Resistance Training–Induced Muscle Hypertrophy in the Elderly

Extended periods of resistance training (RT) induce muscle hypertrophy. Nevertheless, to date, no study has investigated the time window necessary to observe significant changes in muscle cross-sectional area (CSA) in older adults. Therefore, this study investigated the time course of muscle hypertrophy after 10 weeks (20 sessions) of RT in the elderly. Fourteen healthy older subjects were randomly allocated in either the RT (n: 6) or control group (n: 8). The RT was composed of 4 sets × 10 repetitions (70-80% 1 repetition maximum [1RM]) in a leg press machine. The time course of vastus lateralis muscle hypertrophy (CSA) was assessed on a weekly basis by mode-B ultrasonography. Leg press muscle strength was assessed by dynamic 1RM test. Our results demonstrated that the RT group increased leg press 1RM by 42% (p ≤ 0.05) after 10 weeks of training. Significant increases in vastus lateralis muscle CSA were observed only after 18 sessions of training (9 weeks; p ≤ 0.05; 7.1%). In conclusion, our training protocol promoted muscle mass accrual in older subjects, and this was only observable after 18 sessions of RT (9 weeks).

Resistance Training-Induced Muscle Hypertrophy is Associated with Compliment C1q Concentration in Elderly Men

Aging induced the decline in muscle mass and muscle strength, whereas resistance training improves the decreases in muscle mass with aging. Recent study showed that the aging-induced increase in C1q secretion activated muscular Wnt signaling pathway and, consequently, it lead to development of muscle fibrosis. PURPOSE: To clarify whether serum C1q concentration is associated with resistance training-induced increase in muscle mass of elderly men. METHODS: Nineteen male healthy elderly subjects (68.7±7.1 years) assigned either 12-week of resistance training (RT, n=11) or control (CON, n=8) groups. Muscle cross-sectional area (CSA) of the thigh was measured by magnetic resonance imaging (MRI) and serum C1q concentration were determined by ELISA. Additionally, the mRNA level of AXIN2, a target gene of Wnt/β-catenin signaling, and collagen1A1 (COL1A1), as an index of fibrotic change, in skeletal muscle were measured by real-time RT-PCR and compared among RT group at baseline, after exercise intervention and young adults at baseline. RESULTS: The muscle CSA was significantly increased (p < 0.01) and serum C1q concentration was significantly declined after the exercise intervention (p < 0.01), but did not change in CON group. Interestingly, the change in serum C1q concentration was significantly correlated with the change in muscle CSA (r = 0.70, p < 0.05) in RT group Additionally, muscular AXIN2 and COL1A1 mRNA expressions were significantly higher in older adults than in young adults (p < 0.0001 for each). Furthermore, these mRNA expressions were significantly reduced after the exercise intervention (AXIN2 mRNA, P < 0.005; COL1A1, P < 0.05). CONCLUSIONS: These results suggest that the alteration of serum C1q level may be associated with increase in muscle mass by resistance training and serum C1q may be a biomarker of exercise adaptability in elderly men. Supported by Grants-in-Aid for Scientific Research (#26282199 and #25560378 for M. Iemitsu).

Strength training improves cycling performance, fractional utilization of VO2max and cycling economy in female cyclists.

The purpose of this study was to investigate the effect of adding heavy strength training to well-trained female cyclists' normal endurance training on cycling performance. Nineteen female cyclists were randomly assigned to 11 weeks of either normal endurance training combined with heavy strength training (E+S, n = 11) or to normal endurance training only (E, n = 8). E+S increased one repetition maximum in one-legged leg press and quadriceps muscle cross-sectional area (CSA) more than E (P < 0.05), and improved mean power output in a 40-min all-out trial, fractional utilization of VO2 max and cycling economy (P < 0.05). The proportion of type IIAX-IIX muscle fibers in m. vastus lateralis was reduced in E+S with a concomitant increase in type IIA fibers (P < 0.05). No changes occurred in E. The individual changes in performance during the 40-min all-out trial was correlated with both change in IIAX-IIX fiber proportion (r = -0.63) and change in muscle CSA (r = 0.73). In conclusion, adding heavy strength training improved cycling performance, increased fractional utilization of VO2 max , and improved cycling economy. The main mechanisms behind these improvements seemed to be increased quadriceps muscle CSA and fiber type shifts from type IIAX-IIX toward type IIA.

Exercise and medication effects on persons with Parkinson disease across the domains of disability: a randomized clinical trial.

Hypokinesia and bradykinesia as movement deficits of Parkinson disease are thought to be mediated by both basal ganglia dysfunction and a loss of muscle mass and strength commensurate with aging and decreased levels of physical activity. For these reasons, we sought to utilize resistance training as a means to increase muscle force and minimize hypokinesia and bradykinesia in persons with Parkinson disease and examine the effects of exercise and medication on Body Structure and Function (muscle force production and muscle cross-sectional area), Activity (mobility), and Participation (Health Status) outcomes. Forty-two participants were enrolled in a 12-week randomized clinical trial that compared 2 active exercise interventions: a standard care control group (Active Control) and an experimental group that underwent Resistance Exercise via Negative Eccentric Work (RENEW). Participants in both groups improved in muscle force production and mobility as a result of exercise and medication (P < 0.02). There were no significant interaction or between-group differences and no significant changes in muscle cross-sectional area or health status were observed. Effect sizes for exercise and medication combined exceeded the effect sizes of either intervention in isolation. Taken together, these results point to the complementary effects of exercise and medication on the Body Structure and Function and Activity outcomes but little effect on Participation outcomes.Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A92).

OGT and OGA expression in postmenopausal skeletal muscle associates with hormone replacement therapy and muscle cross-sectional area

Protein glycosylation via O-linked N-acetylglucosaminylation (O-GlcNAcylation) is an important post-translational regulatory mechanism mediated by O-GlcNAc transferase (OGT) and responsive to nutrients and stress. OGT attaches an O-GlcNAc moiety to proteins, while O-GlcNAcase (OGA) catalyzes O-GlcNAc removal. In skeletal muscle of experimental animals, prolonged increase in O-GlcNAcylation associates with age and muscle atrophy. Here we examined the effects of hormone replacement therapy (HRT) and power training (PT) on muscle OGT and OGA gene expression in postmenopausal women generally prone to age-related muscle weakness. In addition, the associations of OGT and OGA gene expressions with muscle phenotype were analyzed. Twenty-seven 50–57-year-old women participated in a yearlong randomized placebo-controlled trial: HRT (n=10), PT (n=8) and control (n=9). OGT and OGA mRNA levels were measured from muscle samples obtained at baseline and after one year. Knee extensor muscle cross-sectional area (CSA), knee extension force, running speed and vertical jumping height were measured. During the yearlong intervention, HRT suppressed the aging-associated upregulation of OGT mRNA that occurred in the controls. The effects of PT were similar but weaker. HRT also tended to increase the OGA mRNA level compared to the controls. The change in the ratio of OGT to OGA gene expressions correlated negatively with the change in muscle CSA. Our results suggest that OGT and OGA gene expressions are associated with muscle size during the critical postmenopausal period. HRT and PT influence muscle OGT and OGA gene expression, which may be one of the mechanisms by which HRT and PT prevent aging-related loss of muscle mass.

Natural History of Skeletal Muscle Mass Changes in Chronic Kidney Disease Stage 4 and 5 Patients: An Observational Study

Cross-sectional studies in dialysis demonstrate muscle wasting associated with loss of function, increased morbidity and mortality. The relative drivers are poorly understood. There is a paucity of data regarding interval change in muscle in pre-dialysis and dialysis-dependant patients. This study aimed to examine muscle and fat mass change and elucidate associations with muscle wasting in advanced CKD.134 patients were studied (60 HD, 28 PD, 46 CKD 4–5) and followed up for two years. Groups were similar in age, sex and diabetes prevalence. Soft tissue cross-sectional area (CSA) was measured annually on 3 occasions by a standardised multi-slice CT thigh. Potential determinants of muscle and fat CSA were assessed. Functional ability was assessed by sit-to-stand testing.88 patients completed follow-up (40 HD, 16 PD, 32 CKD). There was a significant difference in percentage change in muscle CSA (MCSA) over year 1, dependant on treatment modality (χ2 = 6.46; p = 0.039). Muscle loss was most pronounced in pre-dialysis patients. Muscle loss during year 1 was partially reversed in year 2 in 39%. Incident dialysis patients significantly lost MCSA during the year which they commenced dialysis, but not the subsequent year. Baseline MCSA, change in MCSA during year 1 and dialysis modality predicted year 2 change in MCSA (adjusted R2 = 0.77, p<0.001). There was no correlation between muscle or fat CSA change and any other factors. MCSA correlated with functional testing, although MCSA change correlated poorly with change in functional ability.These data demonstrate marked variability in MCSA over 2 years. Loss of MCSA in both pre-dialysis and established dialysis patients is reversible. Factors previously cross-sectionally shown to correlate with MCSA did not correlate with wasting progression. The higher rate of muscle loss in undialysed CKD patients, and its reversal after dialysis commencement, suggests that conventional indicators may not result in optimal timing of dialysis initiation.

Inflammation marker, damage marker and anabolic hormone responses to resistance training with vascular restriction in older males

The goal of this study was to examine anabolic hormone, muscle damage marker and inflammation marker responses to two types of resistance training protocols in older men. Thirty-six healthy older males (mean age = 56.6 ± 0.6 years) completed 6 weeks of high-intensity resistance training (HI-RT), low-intensity resistance training with vascular restriction (LI-BFR) or no exercise control group (CON) three times per week. Three upper body exercises were performed by both exercise groups at the same intensity (at 80% 1-RM), but lower body exercises were performed by the HI-RT group at 80% 1-RM and by the LI-BFR group at 20% 1-RM with vascular restriction. Resting serum creatine kinase (CK), interleukin 6 (IL-6), insulin-like growth factor-I (IGF-I), IGF binding protein 3 (IGFBP-3) and testosterone (T) were measured before and after training. No significant group differences in resting CK, IL-6, IGF-I, IGFBP-3 and T were detected following training (P>0.05). In addition, there were no significant changes in muscle cross-sectional area (CSA), but a trend for significant decreases in the percent changes in thigh subcutaneous fat (P = 0.051). Although training-induced anabolic hormone response did not reach statistical significance, our findings on CK and IL-6 indicated that the LI-BFR training protocol was safe and well tolerated for older men to perform to improve muscular strength.

MRT-basierte Messung des Muskelschadens nach minimal-invasiver Hüftprothesenimplantation

Muscle trauma in minimally invasive hip arthroplasty using a direct anterior approach was assessed by magnetic resonance imaging (MRI) in 25 patients preoperatively, as well as 6 months after total hip replacement. The MRI evaluation included the measurement of changes in muscle cross-sectional area (CSA = atrophy) and fatty infiltration of the muscles. Using MRI, preoperatively existing and operatively caused muscle tissue damage could be detected by assessing changes in muscle CSA and fatty infiltration. Even preoperatively, a muscular atrophy and fatty infiltration could be demonstrated in the diseased hip. Using the minimally invasive direct anterior approach, a postoperative significantly reduced CSA and significantly increased fatty degeneration was detected for the M. tensor fasciae latae and the M. glutaeus minimus. No increased damage of the M. glutaeus medius could be detected.

Functional and muscle morphometric effects of ACL reconstruction. A prospective CT study with 1 year follow‐up

Computed tomography (CT) was used to explore if changes in muscle cross-sectional area and quality after anterior cruciate ligament (ACL) injury and reconstruction would be related to knee function. Fourteen females and 23 males (16-54 years) underwent clinical tests, subjective questionnaires, and CT 1 week before and 1 year after ACL surgery with semitendinosus-gracilis (STG) graft and rehabilitation. Postoperatively, knee laxity was decreased and functional knee measures and subjective patient scores improved. The most obvious remaining deficit was the quadriceps atrophy, which was significantly larger if the right leg was injured. Right-leg injury also tended to cause larger compensatory hypertrophy of the combined knee flexor and tibial internal rotator muscles (preoperatively). The quadriceps atrophy was significantly correlated with the scores and functional tests, the latter also being related to the remaining size of the gracilis muscle. Biceps femoris hypertrophy and, in males only, semimembranosus hypertrophy was observed following the ACL reconstruction. The lack of semimembranosus hypertrophy in the women could, via tibial internal rotation torque deficit, contribute to the less favorable functional and subjective outcome recorded for the women. The results indicate that the quadriceps, the combined knee flexor/tibial internal rotator muscles, side of ACL injury, and sex are important to consider in rehabilitation after STG graft.

Strength and hypertrophy with resistance training: chasing a hormonal ghost

I am writing with regards to the article recently published in the European Journal of Applied Physiology by Ronnestad et al. (2011). The authors report in their abstract that ‘‘only L ? A [leg plus arm training—a high ‘anabolic’ hormonal exposure condition] achieved increase in the CSA at the part of the arm flexors with the largest crosssectional area (p \ 0.001), while no changes occurred in A [arm only training—a low ‘anabolic’ hormonal exposure condition].’’ Oddly, examination of Fig. 6 in their paper reveals that significant hypertrophy did occur at two sites (of 4 measured) in the A arm, which is misleading by comparison not only to the statement in their abstract but also to a redrawing of their same figure (see Fig. 1). Additionally, a finding for which incomplete statistical analysis was reported was the change in muscle volume which was not different between the A and the L ? A arms. Since the change in muscle volume would be the product of the change in muscle cross-sectional area (CSA) (see Fig. 1 below) and the length of the muscle, it is hard to reconcile that there were differences in CSA between conditions with no difference in muscle volume change. Do the authors believe that the A arm got longer? A more plausible explanation is that there was no greater change in muscle CSA in the L ? A versus the A arm overall, except for the one site of the largest CSA. It is notable that the statistical comparison of CSA changes or volume changes between the conditions was not reported; however, it would be surprising if those changes in volume or CSA were different. Given the lack of a statistical comparison between arms in terms of hypertrophy, it seems impossible to conclude (from the author’s abstract) that: ‘‘L ? A had favorable muscle adaptations [no definition for ‘favorable muscle adaptations’ is given anywhere in the author’s paper] in elbow flexors compared to A (p \ 0.05). In conclusion, performing leg exercises prior to arm exercises and thereby increasing the levels of serum testosterone and growth hormone induced superior strength training adaptations [also not defined] compared to arm training without acute elevation of hormones.’’ In fact, graphing the changes at each slice for each condition side-by-side shows that the differential hypertrophy, if it existed at all, is trivial (see Fig. 1) and is due to an artifact of not correctly aligning the arm CSA slices in the magnetic resonance (MR) scanner. If all arguments put forward previously are correct, then we can rule out the possibility that differential changes in muscle CSA or volume (i.e., hypertrophy) occurred between the L ? A and A arms. Thus, we are left to conclude that what the arm that trained and was preceded by leg exercises experienced during training was a superior neuromuscular adaptation to account for the greater 1 RM gain in strength. Interestingly, the authors present the progression in training load and show that it was identical between the L ? A and the A arms (Fig. 1). Thus, the arms apparently gained strength during the training program at an equivalent rate and achieved the same final load during training. Yet through some inexplicable mechanism during maximal 1 RM strength testing there was greater strength in the L ? A versus the A arm. This is a surprising observation and one that was not even alluded to in the paper. The rise in hormone levels were certainly not Communicated by Susan A. Ward.

Estimation of changes in volume of individual lower-limb muscles using magnetic resonance imaging (during bed-rest)

Muscle size in the lower limb is commonly assessed in neuromuscular research as it correlates with muscle function and some approaches have been assessed for their ability to provide valid estimates of muscle volume. Work to date has not examined the ability of different measurement approaches (such as cross-sectional area (CSA) measures on magnetic resonance (MR) imaging) to accurately track changes in muscle volume as a result of an intervention, such as exercise, injury or disuse. Here we assess whether (a) the percentage change in muscle CSA in 17 lower-limb muscles during 56 days bed-rest, as assessed by five different algorithms, lies within 0.5% of the muscle volume change and (b) the variability of the outcome measure is comparable to that of muscle volume. We find that an approach selecting the MR image with the highest muscle CSA and then a series of CSA measures, the number of which depended upon the muscle considered, immediately distal and proximal, provided an acceptable estimate of the muscle volume change. In the vastii, peroneal, sartorius and anterior tibial muscle groups, accurate results can be attained by increasing the spacing between CSA measures, thus reducing the total number of MR images and hence the measurement time. In the two heads of biceps femoris, semimembranosus and gracilis, it is not possible to reduce the number of CSA measures and the entire muscle volume must be evaluated. Using these approaches one can reduce the number of CSA measures required to estimate changes in muscle volume by ∼60%. These findings help to attain more efficient means to track muscle volume changes in interventional studies.

A Comparison of Techniques for Estimating Training-Induced Changes in Muscle Cross-Sectional Area

The ability to accurately estimate changes in muscle cross-sectional area (CSA) could be a useful tool for strength and conditioning practitioners to assess the effectiveness of a resistance training program. The purpose of this study was twofold: (a) to compare the reliability of 2 separate anthropometric-based field estimations of thigh muscle CSA with that of a more accurate, sophisticated imaging technique (peripheral quantitative computed tomography [pQCT] scanner) and (b) to determine if the field methods would be sensitive enough to detect changes in CSA during a resistance training program. Twenty-five healthy, untrained men completed 8 weeks of resistance training. Cross-sectional area testing occurred twice before the start of training, for reliability and again every 2 weeks during the study. Testing consisted of a pQCT scan of the right thigh followed by circumference and skinfold measurements. Two separate equations (Moritani and deVries [M + D] and Housh multiple regression [HMR]) were used to estimate CSA from the anthropometric data. The M + D and HMR methods demonstrated intraclass correlations of 0.983 and 0.961, respectively, but both significantly underestimated thigh muscle CSA when compared to the pQCT. This error was consistent, however, and consequently, the field methods were able to demonstrate increases in muscle CSA with a pattern similar to those from the pQCT. Thus, these equations can be useful tools to evaluate an athlete's progress toward the goal of increasing muscle CSA. It is the authors' hope that the present study will increase awareness among practitioners of these useful field methods for estimating training-induced changes in muscle CSA.

Age-Related Differences in Lower-Limb Muscle Cross-Sectional Area and Torque Production in Boys With Duchenne Muscular Dystrophy

Mathur S, Lott DJ, Senesac C, Germain SA, Vohra RS, Sweeney HL, Walter GA, Vandenborne K. Age-related differences in lower-limb muscle cross-sectional area and torque production in boys with Duchenne muscular dystrophy. Objective To examine the relationship between lower-extremity muscle cross-sectional area, muscle strength, specific torque, and age in ambulatory boys with Duchenne muscular dystrophy (DMD) compared with controls. Design Observational cross-sectional study. Setting University research setting. Participants Volunteer sample of boys with DMD (n=22) and healthy control boys (n=10), ages 5 through 14 years. Interventions Not applicable. Main Outcome Measures Maximal muscle cross-sectional area (CSA max) assessed by magnetic resonance imaging of quadriceps, plantarflexors (PFs) and dorsiflexors (DFs), peak isometric torque from dynamometry, and timed functional tests. Results The average CSA max of the triceps surae muscle group was approximately 60% higher in boys with DMD compared with controls (39.1±13.6 cm 2 vs 24.5±9.3 cm 2; P=.002), while the tibialis anterior muscle showed age-appropriate increases in CSA max. The increase in quadriceps CSA max was also distinctly different in boys with DMD compared with controls. Specific torque (ie, peak torque/CSA max) was impaired in all 3 muscles groups, with the knee extensor (KE) and PF muscles showing 4-fold, and the DF muscles 2-fold, higher values in controls compared with boys with DMD. Large age-related gains in specific torque were observed in all 3 muscle groups of control subjects, which were absent in ambulatory boys with DMD. Correlations were observed between performance on functional tasks and quadriceps and PF torque production ( r=−.45 to −.57, P<.05), but not with DF strength. Conclusions Age-related changes in muscle cross-sectional area and specific torque production in lower-extremity muscles showed distinctly different patterns in the KE, PF, and DF muscles of boys with DMD compared with controls.

Muscle and bone follow similar temporal patterns of recovery from muscle-induced disuse due to botulinum toxin injection

If muscle force is a primary source for triggering bone adaptation, with disuse and reloading, bone changes should follow muscle changes. We examined the timing and magnitude of changes in muscle cross-sectional area (MCSA) and bone architecture in response to muscle inactivity following botulinum toxin (BTX) injection. We hypothesized that MCSA would return to baseline levels sooner than bone properties following BTX injection. Female BALB mice (15 weeks old) were injected with 20 μL of BTX (1 U/100 g body mass, n = 18) or saline (SAL, n = 18) into the posterior calf musculature of one limb. The contralateral limb (CON) served as an internal control. MCSA and bone properties were assessed at baseline, 2, 4, 8, 12, and 16 weeks post-injection using in vivo micro-CT at the tibia proximal metaphysis (bone only) and diaphysis. Muscles were dissected and weighed after sacrifice. Significant Group × Leg × Time interactions indicated that the maximal decrease in MCSA (56%), proximal metaphyseal BV/TV (38%) and proximal diaphyseal Ct.Ar (7%) occurred 4 weeks after injection. There was no delay prior to bone recovery as both muscle and bone properties began to recover after this time, but MCSA and BV/TV remained 15% and 20% lower, respectively, in the BTX-injected leg than the BTX-CON leg 16 weeks post-injection. Gastrocnemius mass (primarily fast-twitch) was 14% lower in the BTX-injected leg than the SAL-injected leg, while soleus mass (primarily slow-twitch) was 15% greater in the BTX group than the SAL group. Our finding that muscle size and bone began to recover at similar times after BTX injection was unexpected. This suggested that partial weight-bearing and/or return of slow-twitch muscle activity in the BTX leg may have been sufficient to stimulate bone recovery. Alternatively, muscle function may have recovered sooner than MCSA. Our results indicated that muscle cross-sectional area, while important, may not be the primary factor associated with bone loss and recovery when muscle atrophy is induced through BTX injection. To understand the nature of the interaction between muscle and bone, future work should focus on the functional recovery of individual muscles in relation to bone.

Panoramic ultrasonography is a valid method to measure changes in skeletal muscle cross-sectional area

The purpose of this study was to examine the reliability and validity of the "panoramic" brightness mode ultrasonography (US) method to detect training-induced changes in muscle cross-sectional area (CSA) by comparison with results obtained using magnetic resonance imaging (MRI). Out of 27 young male volunteers, 20 subjects were assigned to training group and seven to non-training control group. Muscle CSAs of vastus lateralis were analyzed by MRI and US before and after 21 weeks of either heavy resistance training or control period. Measured by both the US and MRI, the resistance training induced significant increases (~13-14%, P < 0.001) in muscle CSA, whereas no changes were observed in control group. A high repeatability was found between the two consequent US measurements (intraclass correlation coefficient, ICC of 0.997) with standard error of measurement (SEM) of 0.38 cm(2) and smallest detectable difference of 1.1 cm(2). Validity of the US method against MRI in assessing CSA of VL produced ICC of 0.905 and SEM of 0.87 cm(2) with high limits of agreement analyzed by Bland and Altman method. However, the MRI produced systematically (10 +/- 4%, P < 0.01) larger CSA values than the US method. The US showed high agreement against MRI in detecting changes in muscle CSA (ICC of 0.929, SEM of 0.94 cm(2)). The results of this study showed that the panoramic US method provides repeatable measures of a muscle CSA although MRI produced larger absolute CSA values. Moreover, this US method detects training-induced changes in muscle CSA with a comparable degree of precision to MRI.

Effect of prolonged bed rest on the anterior hip muscles

Prolonged bed rest and inactivity is known to cause muscular atrophy with previous research indicating that muscles involved in joint stabilisation are more susceptible. The anterior hip muscles are important for hip joint function and stability but little is known about the effects of prolonged inactivity on their function. This study investigated the effect of prolonged bed rest on the size of the anterior hip muscles and their pattern of recovery. The effect of resistive vibration exercise (RVE) as a countermeasure to muscle atrophy was also investigated. 12 male participants, randomly assigned to either a control or an exercise group, underwent 8 weeks of bed rest with 6 months follow-up. Changes in muscle cross-sectional area (CSA) of the iliacus, psoas, iliopsoas, sartorius and rectus femoris muscles were measured by magnetic resonance imaging at regular intervals during bed rest and recovery phases. CSAs of iliopsoas and sartorius decreased at the hip joint ( p < 0.05) during bed rest but iliacus, psoas, and rectus femoris CSAs were unchanged ( p > 0.05). No significant difference was found between the two groups for all muscles (all p > 0.1), suggesting inefficacy of the countermeasure in this sample. These findings suggest that prolonged bed rest can result in the atrophy of specific muscles across the hip joint which may affect its stability and function.

Modification of an EMG-assisted biomechanical model for pushing and pulling

Pushing and pulling tasks using carts and material handling devices have become more prevalent in occupational environments in an attempt to reduce the musculoskeletal risks associated with lifting. However, little change in low back disorder rates have been noted as tasks change from lifting to pushing and pulling indicating that we do not understand the mechanics of pushing and pulling well. Biomechanical assessments of pushing and pulling tasks using person-specific biologically assisted models offer a means to help understand how the spine is loaded under pushing and pulling conditions. However, critical components of these models must be adjusted so that they are sensitive to the different physiologic responses in the torso muscles expected during pushing and pulling compared to lifting tasks. The objective of this study was to modify an electromyography (EMG)-assisted biomechanical model designed to evaluate lifting tasks so that it can better represent the biomechanical forces expected during pushing and pulling tasks. Several key modifications were made. Based upon a literature review, changes in muscle cross-sectional area and muscle origins and insertions were made to better represent the geometry of the torso muscles. It was also necessary to adjust the length–force and velocity–force muscle relationships. Empirically derived length–force and velocity–force relationships were developed to independently represent the flexor and extensor musculature. These modifications were then systematically incorporated into the model. The model was exercised over several pushing and pulling conditions to assess the effect of these modifications on its ability to predict externally measured spinal moments. Results indicated that the alterations made to the preexisting EMG-assisted model resulted in acceptable model performance for pushing, pulling, and lifting activities. Relevance to industry The use of carts and material handling devices has become increasingly prevalent in industry, though little research has been done to examine the body's response. The modifications made to the biomechanical model would enable its use in the evaluation and design of material handling devices and pushing and pulling tasks.