Locomotor training and muscle function after incomplete spinal cord injury: case series

BACKGROUND/OBJECTIVE: To determine whether 9 weeks of locomotor training (LT) results in changes in muscle strength and alterations in muscle size and activation after chronic incomplete spinal cord injury (SCI). STUDY DESIGN: Longitudinal prospective case series. METHODS: Five individuals with chronic incomplete SCI completed 9 weeks of LT. Peak isometric torque, torque developed within the initial 200 milliseconds of contraction (Torque 200), average rate of torque development (ARTD), and voluntary activation deficits were determined using isokinetic dynamometry for the knee-extensor (KE) and plantar-flexor (PF) muscle groups before and after LT. Maximum muscle cross-sectional area (CSA) was measured prior to and after LT. RESULTS: Locomotor training resulted in improved peak torque production in all participants, with the largest increases in the more-involved PF (43.9% +/- 20.0%), followed by the more-involved KE (21.1% +/- 12.3%). Even larger improvements were realized in Torque 200 and ARTD (indices of explosive torque), after LT. In particular, the largest improvements were realized in the Torque 200 measures of the PF muscle group. Improvements in torque production were associated with enhanced voluntary activation in both the KE and ankle PF muscles and an increase in the maximal CSA of the ankle PF muscles. CONCLUSION: Nine weeks of LT resulted in positive alterations in the KE and PF muscle groups that included an increase in muscle size, improved voluntary activation, and an improved ability to generate both peak and explosive torque about the knee and ankle joints.     

Surface electrical stimulation of skeletal muscle after spinal cord injury.

STUDY DESIGN: Survey. OBJECTIVE: Examine muscle contractile activity during electrical stimulation (ES) after spinal cord injury (SCI). SETTING: General community of Athens, Georgia, USA. METHODS: Eight clinically complete SCI adults (C6 to T12) 4+/-1 (mean+/-SE) years post injury and eight able-bodied adults were studied. Surface ES was applied to the left m. quadriceps femoris for three sets of 10, 1 s isometric actions (50 Hz trains, 400 micros biphasic pulses, 50 micros phase delay, 1 s: 1 s duty cycle) with 90 s of rest between sets. Current was set to evoke isometric torque that was (1) sufficient to elicit knee extension with 2.3 kg attached to the ankle (low level ES), and (2) intended to equal 30% (mid level ES) or 60% of maximal voluntary torque of able-bodied adults (high level ES, able-bodied only). The absolute and relative cross-sectional area (CSA) of m. quadriceps femoris that was stimulated as reflected by contrast shift in magnetic resonance images and torque were measured. RESULTS: Six+/-2, 20+/-2 and 38+/-4% of the average CSA of m. quadriceps was stimulated during low, mid and high level ES, respectively, for able-bodied. Corresponding values for SCI for low and mid level ES were greater (61+/-12 and 92+/-7%, P = 0.0002). Torque was related to the CSA (cm2) of stimulated muscle (Nm = 3.53 x stimulated CSA+13, r2 = 0.68, P = 0.0010), thus ES of a greater per cent of m. quadriceps femoris in SCI was attributed to their smaller muscle (24+/-3 vs 73+/-5 cm2, P = 0.0001). The decline in torque ranged from 9+/-l to 15+/-4% within and over sets for low, mid or high level ES in able-bodied. SCI showed greater (P = 0.0001) fatigue (19+/-3 to 47+/-6%). CONCLUSION: The territory of muscle activation by surface electrical stimulation varies among SCI patients. Given sufficient current, a large portion of the muscle of interest can be stimulated. The resulting torque is modest, however, compared to that attainable in able-bodied individuals due to the small size and limited fatigue resistance of skeletal muscle years after spinal cord injury.     

Locomotor Training and Muscle Function After Incomplete Spinal Cord Injury: Case Series

Abstract

Background/Objective: To determine whether 9 weeks of locomotor training (LT) results in changes in muscle strength and alterations in muscle size and activation after chronic incomplete spinal cord injury (SCI). Study Design: Longitudinal prospective case series.

Methods: Five individuals with chronic incomplete SCI completed 9 weeks of LT. Peak isometric torque, torque developed within the initial 200 milliseconds of contraction (Torque₂₀₀), average rate of torque development (ARTD), and voluntary activation deficits were determined using isokinetic dynamometry for the knee-extensor (KE) and plantar-flexor (PF) muscle groups before and after LT. Maximum muscle crosssectional area (CSA) was measured prior to and after LT.

Results: Locomotor training resulted in improved peak torque production in all participants, with the largest increases in the more-involved PF (43.9% ± 20.0%), followed by the more-involved KE (21.1% ± 12.3%). Even larger improvements were realized in Torque200 and ARTD (indices of explosive torque), after LT. In particular, the largest improvements were realized in the Torque200 measures of the PF muscle group. Improvements in torque production were associated with enhanced voluntary activation in both the KE and ankle PF muscles and an increase in the maximal CSA of the ankle PF muscles.

Conclusion: Nine weeks of LT resulted in positive alterations in the KE and PF muscle groups that included an increase in muscle size, improved voluntary activation, and an improved ability to generate both peak and explosive torque about the knee and ankle joints.     

Atrophy of non-locomotor muscle in patients with end-stage renal failure.

BACKGROUND: All previous histological studies of skeletal muscles of patients with renal failure have used locomotor muscle biopsies. It is thus unclear to what degree the observed abnormalities are due to the uraemic state and how much is due to disuse. The present study was undertaken to attempt to investigate this question by examining a non-locomotor muscle (rectus abdominis) in patients with end-stage renal failure. METHODS: Biopsies from rectus abdominis were obtained from 22 renal failure patients (RFPs) undergoing surgical Tenchkoff catheter implantation for peritoneal dialysis and 20 control subjects undergoing elective abdominal surgery. Histochemical staining of frozen sections and morphometric analysis was used to estimate the proportion of each fibre type, muscle fibre area and capillary density. Myosin heavy chain composition was examined by SDS-PAGE. RESULTS: There were no differences in fibre type distribution between RFPs and controls. All RFPs showed fibre atrophy [mean cross-sectional area (CSA) 3300 +/- 1100 microm2, compared to 4100 +/- 1100 microm2 in controls (P < 0.05)]. All fibre types were smaller in mean CSA in RFPs than in controls (15, 26 and 28% for types I, IIa and IIx, respectively). These differences could not be accounted for by differences in age, gender or cardiovascular or diabetic comorbidity. Muscle fibre capillarization, expressed as capillaries per fibre or capillary contacts per fibre, was significantly less in RFPs. CONCLUSIONS: Since a non-locomotor muscle was examined, the effects of disuse as a cause of atrophy have been minimized. It is likely, therefore, that the decreased muscle fibre CSA and capillary density of RFPs compared to controls were due predominantly to uraemia itself.     

Skeletal muscle atrophy and increased intramuscular fat after incomplete spinal cord injury

STUDY DESIGN: Cross-sectional and longitudinal design. OBJECTIVES: (1) To quantify skeletal muscle cross-sectional area (CSA) after correcting for intramuscular fat (IMF) in thigh muscle groups 6 weeks after incomplete spinal cord injury (SCI), (2) to monitor the changes in muscle CSA and IMF after 3 months from the initial measurement. SETTING: Academic institution Athens, GA, USA. METHODS: Six incomplete SCI patients (28+/-4 years, 178+/-5 cm and 78+/-6 kg, mean+/-SE, C7 to L3, American Spinal Injury Association B or C) were tested at 5+/-1 weeks and 3 months after the initial measurement. T1-weighted magnetic resonance images were taken of both thighs. Six able-bodied (AB) controls were matched in age, sex, height and weight (29+/-4 years, four male and two female subjects, 179+/-5 cm and 77+/-6 kg). RESULTS: At 6 weeks post-injury, muscle CSA was 82+/-4 cm(2) in incomplete SCI and 123+/-21 cm(2) in AB controls (P=0.04). IMF CSA was 5.2+/-1.3 and 2.3+/-0.6 cm(2) in incomplete SCI and AB controls, respectively (P=0.03). Relative IMF was three-fold higher (P=0.03) in the SCI group versus AB controls (5.8+/-1.4 versus 2.0+/-0.6%). After 3 months, IMF increased 26% in the SCI group compared to the initial measurement (P=0.02). CONCLUSIONS: Skeletal muscle atrophy is associated with greater IMF accumulation in SCI group 6 weeks post-injury compared to AB controls. Moreover, IMF continues to increase over time in incomplete SCI.     

Spasticity may defend skeletal muscle size and composition after incomplete spinal cord injury

DESIGN: Cross-sectional. OBJECTIVES: (1) To determine the effects of the level of spinal cord injury (SCI) on skeletal muscle, intramuscular fat (IMF) cross-sectional areas (CSAs) and relative IMF; (2) to determine the relation, if any, of spasticity to each of these variables after incomplete SCI. SETTINGS: In-patient study at the Shepherd Center, Atlanta, GA, USA. METHODS: Thirteen individuals with incomplete SCI were classified according to their level of injury into a high level of injury group (HLI, C5-C7, n=8) and a low level of injury group (LLI, T12-L2, n=5). Spasticity was determined for thigh muscles using a modified Ashworth scale at 6 weeks post-injury. T1-weighted magnetic resonance (MR) images were taken 6 weeks post-injury to measure thigh skeletal muscle and IMF CSAs. RESULTS: Spasticity was significantly evident in the HLI group compared to the LLI group (P=0.023). Six weeks post-injury, muscle CSA was 103+/-18 cm(2) in the HLI group and 80+/-20 cm(2) in the LLI group (P=0.042). Relative IMF was 3.6+/-2.0% in HLI and 7.5+/-4.0% in LLI (P=0.021). Additionally, spasticity accounted for 54% of the variability in muscle CSA for all subjects (r (2)=0.54, P=0.006). CONCLUSIONS: Spasticity may be an important factor in defending skeletal muscle size and indirectly preventing IMF accumulation early after incomplete SCI.     

Early quadriceps strength loss after total knee arthroplasty. The contributions of muscle atrophy and failure of voluntary muscle activation

BACKGROUND: While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in the early loss of quadriceps strength after surgery. METHODS: Twenty patients with unilateral knee osteoarthritis were tested an average of ten days before and twenty-seven days after primary total knee arthroplasty. Quadriceps strength and voluntary muscle activation were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on a maximum voluntary isometric contraction. Maximal quadriceps cross-sectional area was assessed with use of magnetic resonance imaging. RESULTS: Postoperatively, quadriceps strength was decreased by 62%, voluntary activation was decreased by 17%, and maximal cross-sectional area was decreased by 10% in comparison with the preoperative values; these differences were significant (p < 0.01). Collectively, failure of voluntary muscle activation and atrophy explained 85% of the loss of quadriceps strength (p < 0.001). Multiple linear regression analysis revealed that failure of voluntary activation contributed nearly twice as much as atrophy did to the loss of quadriceps strength. The severity of knee pain with muscle contraction did not change significantly compared with the preoperative level (p = 0.31). Changes in knee pain during strength-testing did not account for a significant amount of the change in voluntary activation (p = 0.14). CONCLUSIONS: Patients who are managed with total knee arthroplasty have profound impairment of quadriceps strength one month after surgery. This impairment is predominantly due to failure of voluntary muscle activation, and it is also influenced, to a lesser degree, by muscle atrophy. Knee pain with muscle contraction played a surprisingly small role in the reduction of muscle activation.     

Effect of nitrous oxide on human skeletal muscle function

Background: Nitrous oxide (N₂O) is commonly administered in conjunction with parturition, which requires the performance of repeated high-force voluntary muscle actions. Therefore, we examined the effect of a subanesthetic dose of N₂O on the force-velocity relationship of the quadriceps femoris muscle.
Methods: Nine healthy subjects performed maximal voluntary muscle actions once while breathing air and once while breathing a normoxic gas mixture containing 35% (N₂O). Peak torque of the knee extensors was measured during concentric muscle contractions at different angular velocities (30, 60, 90, 150 and 210°s^-1), and eccentric (30, 60, 90 and 150°s^-1) and isometric (knee-joint angle=60°) muscle actions. Maximal angular velocity was determined during unloaded knee extensions.
Results: N₂O decreased peak torque at any given angular velocity. The overall decrease in peak torque averaged 4.8±2.2% (P<0.001). Likewise, N₂O decreased maximal angular velocity by 5.7±4.3% (P<0.01). Thus, the impairment in muscle function induced by a 35% N₂O is only minute and hence most likely of little significance in clinical practice.     

Early neuromuscular electrical stimulation to optimize quadriceps muscle function following total knee arthroplasty: a case report

STUDY DESIGN: Case report. BACKGROUND: Following total knee arthroplasty (TKA), restoration of normal quadriceps muscle function is rare. One month after surgery, quadriceps torque (force) is only 40% of preoperative values and quadriceps activation is only 82% of preoperative levels, despite initiating postoperative rehabilitation the day after surgery. Early application of neuromuscular electrical stimulation (NMES) offers a possible approach to minimize loss of quadriceps torque more effectively than traditional rehabilitation exercises alone. CASE DESCRIPTION: A 65-year-old female underwent a right, cemented TKA. Isometric quadriceps and hamstrings muscle torque were measured preoperatively and at 3, 6, and 12 weeks after TKA. Quadriceps muscle activation was measured using a doublet interpolation technique at the same time points. The patient participated in a traditional TKA rehabilitation program augmented by NMES, which was initiated 48 hours after surgery and continued twice a day for the first 3 weeks, and once daily for 3 additional weeks. OUTCOMES: Preoperatively, the involved quadriceps produced 75% of the torque of the uninvolved side and demonstrated only 72.9% activation. At 3, 6, and 12 weeks after TKA, quadriceps torque was greater than the preoperative values of the involved side by 16%, 29%, and 56%, respectively. Similarly, activation improved to 93.4%, 94.6%, and 93.5% at 3, 6, and 12 weeks after TKA. DISCUSSION: Mitigating quadriceps muscle weakness immediately after TKA using early NMES may improve functional outcomes, because quadriceps weakness has been associated with numerous functional limitations and an increased risk for falls. Despite presenting preoperatively with substantial quadriceps torque and activation deficits, the patient in this case demonstrated improvements in quadriceps function at all the times measured, all of which were superior to those reported in the literature. The patient also made substantial improvements in functional outcomes, including the Knee Injury and Osteoarthritis Outcome Score (KOOS), 6-minute walk test, timed up and go (TUG) test, stair-climbing test, and the SF-36 Physical Component Score. Appropriately controlled clinical trials will be necessary to determine whether such favorable outcomes following TKA are specifically attributable to the addition of NMES to the rehabilitation program.     

Reduced muscle radiological density, cross-sectional area, and strength of major hip and knee muscles in 22 patients with hip osteoarthritis

BACKGROUND: Patients with hip osteoarthritis (OA) typically suffer joint pain, and often experience muscular weakness. We hypothesized that substantial atrophy would manifest in multiple muscle groups along the affected limb, resulting in severe muscle dysfunction. PATIENTS AND METHODS: We assessed 22 elderly patients with unilateral OA for maximal voluntary isometric strength of hip and knee muscles using a dynamometer that was developed for the purpose. Cross-sectional area (CSA) and radiological density (RD; in Hounsfield units: HU) of hip and knee muscles were assessed using CT. We determined SF-36, HHS, and EQ-5D. RESULTS: Hip extension, flexion, adduction, abduction, and knee extension strength were reduced (11- 29%; p < 0.01) in the OA limb relative to the healthy limb. Muscle CSA of hip extensors, flexors, adductors, knee extensors and flexors, but not hip abductors, was reduced (11-19%; p < 0.01) in the OA limb, where RD of all muscle groups except hip flexors was reduced (5-15 HU; p < 0.01). The clinical scores confirmed impairment. INTERPRETATION: Major muscles functioning around the hip and knee showed substantial loss of strength and mass, which contributes to the reduced ambulatory capacity of OA patients. Reduced muscle CSA could not fully explain the loss in strength. Infiltration with fat or other non-contractile components, as indicated by a reduced RD, in OA limb muscles was substantial.     

Muscle atrophy in patients receiving hemodialysis: effects on muscle strength,muscle quality,and physical function

BACKGROUND: Dialysis patients are less active and have reduced functional capacity compared to individuals with normal renal function. Muscle atrophy and weakness may contribute to these problems. This investigation was undertaken to quantify the extent of atrophy in the lower extremity muscles, to determine whether defects in muscle specific strength (force per unit mass) or central nervous system (CNS) activation are present, and to assess the relationship between muscle size and physical performance in a group of patients on hemodialysis. METHODS: Thirty-eight dialysis subjects (aged 55 +/- 15 years) and nineteen healthy sedentary controls (aged 55 +/- 13 years) were enrolled. Magnetic resonance imaging of the lower leg was used to determine the total cross-sectional area (CSA) and the area of contractile and non-contractile tissue of the ankle dorsiflexor muscles. Isometric dorsiflexor strength was measured during a maximal voluntary contraction with and without superimposed tetanic stimulation (N = 22 for dialysis subjects, N = 12 for controls). Physical activity was measured by accelerometry, and gait speed was recorded as a measure of physical performance. RESULTS: Dialysis subjects were weaker, less active, and walked more slowly than controls. Total muscle compartment CSA was not significantly different between dialysis subjects and controls, but the contractile CSA was smaller in the dialysis patients even after adjustment for age, gender, and physical activity. Central activation and specific strength were normal. Gait speed was correlated with contractile CSA. CONCLUSIONS: Significant atrophy and increased non-contractile tissue are present in the muscle of patients on hemodialysis. The relationship between contractile area and strength is intact in this population. Muscle atrophy is associated with poor physical performance. Thus, interventions to increase physical activity or otherwise address atrophy may improve performance and quality of life.     

Lower extremity skeletal muscle function in persons with incomplete spinal cord injury

STUDY DESIGN: A cross-sectional study design. OBJECTIVES: To characterize and specifically quantify impairments in muscle function after chronic incomplete spinal cord injury (SCI). SETTING: University of Florida, Gainesville, FL, USA. METHODS: Voluntary and electrically elicited contractile measurements were performed and voluntary activation deficits were quantitatively determined in the knee extensor and ankle plantar flexor muscle groups in 10 individuals with chronic incomplete SCI (C5-T8, ASIA C or D) and age-, gender-, height- and body weight matched healthy controls. RESULTS: Persons with incomplete-SCI were able to produce only 36 and 24% of the knee extensor torque and 38 and 26% of the plantar flexor torque generated by noninjured controls in the self-reported less-involved and more-involved limbs, respectively (P<0.05). In addition, both indices of explosive or instantaneous muscle strength, torque200 (absolute torque reached at 200 ms) and the average rate of torque development (ARTD) were dramatically reduced in the ankle plantar flexor and knee extensor muscle groups in persons with incomplete-SCI. However, the deficit in instantaneous muscle strength was most pronounced in the ankle plantar flexor muscles, with an 11.7-fold difference between the torque200 measured in the self-reported more involved limb and a 5-fold difference in the less-involved limb compared to control muscles. Voluntary activation deficits ranged between 42 and 66% in both muscle groups. Interestingly, electrically elicited contractile properties did not differ between the groups. CONCLUSION: The resultant impact of incomplete-SCI is that affected muscles not only become weak, but slow to develop voluntary torque. We speculate that the large deficit in torque200 and ARTD in the ankle plantar flexors muscles of persons with incomplete-SCI may limit locomotor function. The results presented in this study provide a quantitative and sensitive assessment of muscle function upon which future research examining rehabilitation programs aimed at restoring muscle function and promoting functional recovery after incomplete-SCI may be based.     

A comparison of the effects of electrode placement, muscle tension, and isometric torque of the knee extensors

Numerous electrical stimulation (ES) papers have been published using a variety of electrode placements and muscle tension criteria levels, making cross-comparisons difficult. The purpose of this study was to compare isometric knee extensor torques produced using three methods to induce muscle tension and three electrode placements. Twenty-three healthy, informed female volunteers (mean age = 24 yrs, SD = 3.2 yrs) participated in a practice session and three test sessions, each approximately 48 hrs apart. One of three electrode placements was randomly assigned during each test session. Maximal voluntary isometric contractions (MVIC) preceded the electrically induced isometric torque outputs. Comfortably tolerable and maximally tolerable ES intensities were combined with each of the following electrode placements: 1) lumbosacral plexus/femoral triangle (LS), 2) femoral triangle/transverse distal quadriceps (F), and 3) transverse proximal/distal quadriceps muscle (Q). A two-way ANOVA with repeated measures, Neuman-Keuls, and tests of simple main effects were used to analyze the data. Significantly greater torques were produced during the MVlCs than during either type of electrically induced isometric torque output (p < 0.05). During ES, the maximally tolerable intensity level produced significantly greater torques than the comfortably tolerable intensity level (p < 0.05). The F and Q electrode placements produced similar torques, both significantly greater than the torque produced with the LS electrode placement (p < 0.05). The method to induce muscle tension (voluntary or electrically induced), the criteria defining the level of muscle tension (MVIC, maximally or comfortably tolerable ES), and the electrode placement (LS, F, or Q) affect knee extensor torques and should be considered when using ES and when interpreting ES studies. Although the ideal rehabilitation program typically includes voluntary exercise to provide overload, certain pathologies may contradict this choice. In its place, ES has the potential to minimize strength losses or create gains while offering joint protection. J Orthop Sports Phys Ther 1992;15(4):168-174.     

A mechanical comparison and review of transverse,step-cut,and sigmoid osteotomies

Successful incorporation of massive allografts for the treatment of bone deficiency demands maximizing biologic and mechanical factors. These factors have yet to be mastered, as evidenced by the 8% to 17% nonunion and the 5% to 20% fracture rate. The current study addresses the allograft incorporation process by examining the three construct geometries: transverse, step-cut, and sigmoid. Specimens were plated and mounted on a mechanical testing machine. A rotational displacement was applied, and torsional stiffness (N-m/ degrees ), maximum torque (N-m), and maximum displacement ( degrees ) were calculated. The sigmoid osteotomies had a torsional stiffness of 1.90 +/- 0.68 N-m/ degrees and maximum torque of 18.85 +/- 6.63 N-m versus 0.99 +/- N-m/ degrees and 14.48 +/- 2.15 N-m for the transverse osteotomies; and a maximum angular displacement of 11.60 degrees +/- 1.78 degrees versus 5.73 degrees +/- 1.6 degrees for the step-cut osteotomies. The step-cut osteotomies consistently failed at the step-cut corners, which acted as stress risers. Computer-aided solid modeling of the contact surfaces showed that the step and sigmoid osteotomy areas were 74% and 44%, respectively, larger than the transverse osteotomy. The sigmoid osteotomy, created with a template and pneumatic drill, seems to offer a mechanical advantage over the transverse and step-cut osteotomies by increasing stability and contact surface area relative to the transverse osteotomy but reducing the stress-riser effect of the step-cut osteotomy.     

Equal effectiveness of electrical and volitional strength training for quadriceps femoris muscles after anterior cruciate ligament surgery

Neuromuscular electrical stimulation and voluntary muscle contraction are two exercise modes widely used in rehabilitation to strengthen skeletal muscle. Since there is debate as to which mode is most effective, we compared electrical stimulation with voluntary contraction performed at matched intensities following reconstructive surgery of the anterior cruciate ligament. Forty men and women, aged 15–44, were randomly assigned to either an electrical stimulation or a voluntary contraction group. None of the subjects had a previous history of neuromuscular injury. The subjects received treatment for 30 minutes a day, 5 days a week, for 4 weeks. Knee extension torque was monitored during treatment to try to match the absolute muscular tensions (quantified as “activity”) achieved during therapy. To match the activity of the subjects in the electrical stimulation group, who were treated at the highest stimulation intensity they could tolerate, the subjects in the voluntary contraction group were paced at progressively increasing intensities corresponding to 15, 25, 35, and 45% of the injured limb's maximum voluntary torque during weeks 1, 2, 3, and 4, respectively. We found no significant difference between the groups in terms of maximum voluntary knee extension torque throughout the study period. In addition, 1 year after surgery, there was still no significant difference between groups with regard to knee extension torque (p > 0.4). These data suggest that neuromuscular electrical stimulation and voluntary muscle contraction treatments, when performed at the same intensity, are equally effective in strengthening skeletal muscle that has been weakened by surgical repair of the anterior cruciate ligament.     

Effect of oral creatine supplementation on human muscle GLUT4 protein content after immobilization

The purpose of this study was to investigate the effect of oral creatine supplementation on muscle GLUT4 protein content and total creatine and glycogen content during muscle disuse and subsequent training. A double-blind placebo-controlled trial was performed with 22 young healthy volunteers. The right leg of each subject was immobilized using a cast for 2 weeks, after which subjects participated in a 10-week heavy resistance training program involving the knee-extensor muscles (three sessions per week). Half of the subjects received creatine monohydrate supplements (20 g daily during the immobilization period and 15 and 5 g daily during the first 3 and the last 7 weeks of rehabilitation training, respectively), whereas the other 11 subjects ingested placebo (maltodextrine). Muscle GLUT4 protein content and glycogen and total creatine concentrations were assayed in needle biopsy samples from the vastus lateralis muscle before and after immobilization and after 3 and 10 weeks of training. Immobilization decreased GLUT4 in the placebo group (-20%, P < 0.05), but not in the creatine group (+9% NS). Glycogen and total creatine were unchanged in both groups during the immobilization period. In the placebo group, during training, GLUT4 was normalized, and glycogen and total creatine were stable. Conversely, in the creatine group, GLUT4 increased by approximately 40% (P < 0.05) during rehabilitation. Muscle glycogen and total creatine levels were higher in the creatine group after 3 weeks of rehabilitation (P < 0.05), but not after 10 weeks of rehabilitation. We concluded that 1) oral creatine supplementation offsets the decline in muscle GLUT4 protein content that occurs during immobilization, and 2) oral creatine supplementation increases GLUT4 protein content during subsequent rehabilitation training in healthy subjects.     

Gender comparison of hip muscle activity during single-leg landing

STUDY DESIGN: Controlled laboratory study. OBJECTIVES: To determine whether gender differences in electromyographic (EMG) activity of hip-stabilizing muscles are present during single-leg landing. BACKGROUND: Numerous factors may explain the greater rate of anterior cruciate ligament (ACL) injuries in female athletes. However, gender differences in hip muscle activity during dynamic events have not been well characterized. METHODS AND MEASURES: Twenty-two Division I collegiate athletes (13 female, 9 male) performed drop landings from 30.5- and 45.8-cm heights. Surface EMG was used to examine relative muscle activity from 200 milliseconds prior to initial contact to 250 milliseconds postcontact. Peak and mean values for each muscle (gluteus maximus, gluteus medius, rectus femoris) in each time epoch were analyzed using 2 x 2 (group by height) analyses of variance (ANOVAs) to determine significance. RESULTS: Females demonstrated lower gluteus maximus peak (mean +/- SD, 69.5 +/- 30.2 versus 98.0 +/- 33.4 percent maximum voluntary contraction [%MVIC]; P= .019) and mean (mean +/- SD, 37.5 +/- 15.6 versus 53.9 +/- 18.0 %MVIC; P = .018) muscle activation during the postcontact phase of landing than males. Furthermore, females demonstrated greater peak rectus femoris activity during the precontact phase (mean +/- SD, 33.6 +/- 18.5 versus 18.7 +/- 8.2 %MVIC; P = .029). A positive effect of drop height on relative activity of all muscles was observed during both phases (P<.05). CONCLUSIONS: Females utilize different muscular activation patterns compared to males (ie, decreased gluteus maximus and increased rectus femoris muscle activity) during landing maneuvers. Decreased hip muscle activity and increased quadriceps activity may be important contributors to the increased susceptibility of female athletes to noncontact ACL injuries.     

Investigation of skeletal muscle quantity and quality in end‐stage renal disease

Aim: A more precise understanding of the aetiology and sequelae of muscle wasting in end‐stage renal disease (ESRD) is required for the development of effective interventions to target this pathology. Methods: We investigated 49 patients with ESRD (62.6 ± 14.2 years, 0.3–16.7 years on haemodialysis). Thigh muscle cross‐sectional area (CSA), intramuscular lipid and intermuscular adipose tissue (IMAT) were measured via computed tomography as indices of muscle quantity (i.e. CSA) and quality (i.e. intramuscular lipid and IMAT). Additional health and clinical measures were investigated to determine associations with these variables. Results: Age, energy intake, disease burden, pro‐inflammatory cytokines, nutritional status, strength and functioning were related to muscle quantity and quality. Potential aetiological factors entered into forward stepwise regression models indicated that hypoalbuminaemia and lower body mass index accounted significantly and independently for 32% of the variance in muscle CSA (r = 0.56, P < 0.001), while older age and interleukin‐8 accounted for 41% of the variance in intramuscular lipid (r = 0.64, P < 0.001) and body mass index accounted for 45% of the variance in IMAT (r = 0.67, P < 0.001). Stepwise regression models revealed that intramuscular lipid was independently predictive of habitual gait velocity and 6 min walk distance, while CSA was independently predictive of maximal isometric strength (P < 0.05). Conclusion: Ageing, poor nutritional status and elevated interleukin‐8 are factors potentially contributing to the loss of muscle quality and quantity in ESRD. These deficits can predict functional impairments, with intramuscular lipid accumulation most closely related to decline of submaximal musculoskeletal performance (walking), and low muscle CSA most closely related to decline of maximal performance (peak isometric strength).     

Relationship between abdominal and pelvic floor muscle activation and intravaginal pressure during pelvic floor muscle contractions in healthy continent women

AIM: Activation of the abdominal muscles might contribute to the generation of a strong pelvic floor muscle contraction, and consequently may contribute to the continence mechanism in women. The purpose of this study was to determine the abdominal muscle activation levels and the patterns of muscle activity associated with voluntary pelvic floor muscle (PFM) contractions in urinary continent women. METHODS: Fifteen healthy continent women participated. They performed three maximal contractions of each of the four abdominal muscles and of their PFMs while in supine. Abdominal and PFM activity was recorded using electromyography (EMG), and intravaginal pressure was recorded using a custom modified Femiscan probe. RESULTS: During voluntary maximal PFM contractions, rectus abdominus was activated to 9.61 (+/-7.42)% maximal voluntary electrical activity (MVE), transversus abdominus was activated to 224.30(+/-47.4)% MVE, the external obliques were activated to 18.72(+/-13.33)% MVE, and the internal obliques were activated to 81.47(+/-63.57)% MVE. A clear pattern of activation emerged, whereby the transversus abdominus, internal oblique, and rectus abdominus muscles worked with the PFM in the initial generation of maximal intravaginal pressure. PFM activity predominated in the initial rise in lower vaginal pressure, with later increases in pressure (up to 70% maximum pressure) being associated with the combined activation of the PFM, rectus abdominus, internal obliques, and transverses abdominus. These abdominal muscles were the primary source of intravaginal pressure increases in the latter 30% of the task, whereas there was little increase in PFM activation from this point on. The external oblique muscles showed no clear pattern of activity, but worked at approximately 20% MVE throughout the PFM contractions, suggesting that their role may be predominantly in postural setting prior to the initiation of intravaginal pressure increases. CONCLUSIONS: Defined patterns of abdominal muscle activity were found in response to voluntary PFM contractions in healthy continent women.