Individual distribution of muscle hypertrophy among hamstring muscle heads: Adding muscle volume where you need is not so simple.

PURPOSE: The aim of this study was to determine whether a 9-week resistance training program based on high load (HL) versus low load combined with blood flow restriction (LL-BFR) induced a similar (i) distribution of muscle hypertrophy among hamstring heads (semimembranosus, SM; semitendinosus, ST; and biceps femoris long head, BF) and (ii) magnitude of tendon hypertrophy of ST, using a parallel randomized controlled trial. METHODS: A total of 45 participants were randomly allocated to one of three groups: HL, LL-BFR, and control (CON). Both HL and LL-BFR performed a 9-week resistance training program composed of seated leg curl and stiff-leg deadlift exercises. Freehand 3D ultrasound was used to assess the changes in muscle and tendon volume. RESULTS: The increase in ST volume was greater in HL (26.5 ± 25.5%) compared to CON (p = 0.004). No difference was found between CON and LL-BFR for the ST muscle volume (p = 0.627). The change in SM muscle volume was greater for LL-BFR (21.6 ± 27.8%) compared to CON (p = 0.025). No difference was found between HL and CON for the SM muscle volume (p = 0.178).There was no change in BF muscle volume in LL-BFR (14.0 ± 16.5%; p = 0.436) compared to CON group. No difference was found between HL and CON for the BF muscle volume (p = 1.0). Regarding ST tendon volume, we did not report an effect of training regimens (p = 0.411). CONCLUSION: These results provide evidence that the HL program induced a selective hypertrophy of the ST while LL-BFR induced hypertrophy of SM. The magnitude of the selective hypertrophy observed within each group varied greatly between individuals. This finding suggests that it is very difficult to early determine the location of the hypertrophy among a muscle group.

Factors associated with persistent opioid use 6-12 months after primary total knee arthroplasty.

Persistent pain following knee arthroplasty occurs in up to 20% of patients and may require ongoing analgesia, including extended opioid administration. A comprehensive secondary analysis was performed from results of a study that considered persistent postoperative pain in 242 patients who underwent unilateral knee arthroplasty using a standardised enhanced recovery programme. Opioid prescribing for 12 months before and 12 months after surgery was evaluated and converted to oral morphine equivalents. Demographic, functional, psychological and pain questionnaires were completed along with quantitative sensory testing and genetic analysis. Forty-nine percent of patients had at least one opioid prescription in the 12 months before surgery. Opioid prescriptions were filled in 93% of patients from discharge to 3 months and in 27% of patients ≥6 months after surgery. Persistent opioid use ≥6 months after surgery was strongly associated with pre-operative opioid use (RR 3.2, p < 0.001 (95%CI 1.9-5.4)). The median (IQR [range]) oral morphine equivalent daily dose was 3.6 (0.9-10.5 [0-100.0]) mg pre-operatively, 35.0 (22.5-52.5 [4.6-180.0]) mg in hospital, 12.8 (5.1-24.8 [0-57.9]) mg from discharge to 3 months and 5.9 (4.5-12.0 [0-44.5]) mg at ≥6 months following surgery. Predictors of increased daily oral morphine equivalent ≥6 months after surgery included increased average daily oral morphine equivalent dose compared with previous values (lag), increased body mass index and three or more comorbid pain sites. Persistent opioid use was not associated with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain (RR 1.003, p = 0.655, 95%CI 0.65-1.002) or WOMAC function (RR 1.001, p = 0.99, 95%CI 0.99-1.03) outcomes 6 months after surgery. There was no association between persistent opioid use and pre-operative quantitative sensory testing results or psychological distress. Pre-operatively, patients with a higher body mass index, more comorbid pain sites and those who had filled an opioid prescription in the last 12 months, were at increased risk of persistent opioid use and a higher oral morphine equivalent daily dose ≥ 6 months after surgery. Strategies need to be developed to limit dose and duration of persistent opioid use in patients following knee arthroplasty surgery.

Steroids to reduce the impact on delirium (STRIDE): a double-blind, randomised, placebo-controlled feasibility trial of pre-operative dexamethasone in people with hip fracture.

Neuro-inflammation may be important in the pathogenesis of postoperative delirium following hip fracture surgery. Studies have suggested a potential role for steroids in reducing postoperative delirium; however, the potential efficacy and safety of pre-operative high-dose dexamethasone in this specific population is largely unknown. Conducting such a study could be challenging, considering the multidisciplinary team involvement and the emergency nature of the surgery. The aim of this study was to assess feasibility and effectiveness of dexamethasone given as early as possible following hospital admission for hip fracture, to inform whether a full-scale trial is warranted. This single-centre, randomised, double-blind, placebo-controlled study randomly allocated 79 participants undergoing hip fracture surgery to dexamethasone 20 mg or placebo pre-operatively. Eligibility and recruitment rates, timing of the intervention and adverse events were recorded. Incidence and severity of postoperative delirium were assessed using the 4AT delirium screening tool and the Memorial Delirium Assessment Scale. Postoperative pain, length of stay and mortality were also assessed. The eligibility rate for inclusion was 178/527 (34%), and 57/178 (32%) of eligible patients presented to hospital when no researcher was available (e.g. after-hours, weekends, public holidays). Recruitment was limited mainly by ethical limitations (not including patients with impaired cognition) and lack of weekend staffing. Median (IQR [range]) time from emergency department admission to drug administration was 13.3 (5.9-17.6 [1.8-139.6]) hours. There was a significant difference in delirium severity scores, favouring the dexamethasone group: median (IQR [range]) 5 (3-6 [3-7]) vs. 9 (6-13 [5-14]) in the placebo group, with the probability of superiority effect size being 0.89, p = 0.010. Delirium incidence did not differ between groups: 6/40 (15%) in the dexamethasone group vs. 9/39 (23%) in the placebo group, relative risk (95%CI) 0.65 (0.22-1.65), p = 0.360). A larger randomised controlled trial is feasible and ideally this should include people with existing cognitive impairment, seven days-a-week cover and a multicentre design.

Persistent postoperative pain after total knee arthroplasty: a prospective cohort study of potential risk factors.

BACKGROUND: Persistent postoperative pain (PPP) is common after total knee arthroplasty (TKA). The primary aim of this prospective cohort study was to identify important predictors of moderate to severe PPP 6 and 12 months after TKA. METHODS: Consenting patients (n=300) undergoing primary unilateral TKA attended a preoperative session to collect clinical information (age, gender, BMI, preoperative knee pain, comorbid pain, likely neuropathic pain) and psychological variables (depression, anxiety, catastrophising, expected pain). Quantitative sensory testing (pressure pain thresholds, temporal summation, conditioned pain modulation) was performed, and blood samples were obtained for subsequent genotyping of OPRM1 and COMT. Acute postoperative pain was measured at rest and during movement. Surgical factors (surgery time, patella resurfacing, anaesthetic type) were collected after operation. Follow-up questionnaires were sent 6 and 12 months after surgery. Multivariate logistic regression was used to identify predictors of PPP. RESULTS: The prevalence of moderate to severe PPP was 21% (n=60) and 16% (n=45) 6 and 12 months after surgery, with 55% (n=33) and 60% (n=31) of PPP likely neuropathic in nature. At 6 months, a combination of preoperative pain intensity, expected pain, trait anxiety, and temporal summation (Akaike information criterion, 309.9; area under receiver operating characteristic (ROC) curve, 0.70) was able to correctly classify 66% of patients into moderate to severe PPP and no to mild PPP groups. At 12 months, preoperative pain intensity, expected pain, and trait anxiety (Akaike information criterion, 286.8; area under ROC curve, 0.66) correctly classified 66% of patients. CONCLUSIONS: Findings from this study highlight several factors that may be targeted in future intervention studies to reduce the development of PPP. TRIAL REGISTRY NUMBER: ACTRN12612001089820.

Transcranial direct current stimulation for upper limb neuropathic pain: A double-blind randomized controlled trial.

BACKGROUND: While promising, there are mixed findings for the efficacy of transcranial direct current stimulation (tDCS) for the management of chronic pain. The goal of this study was to evaluate the effect of anodal tDCS on pain and function in people with upper limb neuropathic pain. METHODS: The study was a double-blinded, randomized controlled trial. Thirty participants were randomly allocated into active and sham tDCS groups. Baseline assessments of pain and function, as well as quantitative sensory testing (QST) to probe the function of the nociceptive system, were undertaken prior to participants receiving 5 days of active or sham anodal tDCS (1 mA) over the primary motor cortex. The outcome measures were re-assessed 1, 3 and 8 weeks following the intervention. RESULTS: Group analyses revealed no significant improvement in pain, function, or QST measures over time in either group. However, there were significantly more individual responders (≥30% change in pain) in the active compared to the sham tDCS group at the final follow-up. In the active group, there was a significant correlation indicating those with higher baseline pain had greater pain relief. CONCLUSIONS: On group analyses, no evidence was provided that 1 mA tDCS is beneficial for people with upper limb neuropathic pain, although it may provide lasting pain relief for some individuals. SIGNIFICANCE: At the group level, we found no evidence that 5 days of active 1 mA tDCS is effective for people with upper limb neuropathic pain. However, there were more individual responders in the active tDCS group compared to sham, and those who responded early after treatment experienced sustained pain relief.

TENS Alleviates Muscle Weakness Attributable to Attenuation of Ia Afferents.

Quadriceps weakness is a notable problem following knee damage. Research has shown effectiveness of TENS in improving Quadriceps weakness associated with arthrogenic muscle inhibition. However, these studies were not focused upon short term delivery of TENS, nor did they examine the potential mechanism(s). The present study examined the effect of 25-30 s of TENS upon weakness induced temporarily by a prolonged vibration. Subjects performed eccentric MVCs under 2 conditions (TENS and no-TENS). First, MVC was measured at baseline. For the TENS condition, TENS was applied to each subject's knee joint during a second MVC measurement after vibration. For no-TENS condition, TENS was not applied during the 2nd MVC measurement. MVC between pre-and post-vibration stimulation were compared across the 2 conditions. The results showed that MVC and EMG of TENS-condition was larger than that of no-TENS condition. Our results suggest that TENS could partially restore α-motoneuron activation, despite the induced dysfunctional γ-loop. These results suggest that mechanisms independent of the γ-loop such as a direct facilitation of the QF α-motoneuron pool by a long latency spinal-reflex and/or supraspinal mechanisms appear more likely to be responsible. The findings provide further support for utilizing TENS, even when γ-loop dysfunction is present following joint damage.

Effects of hip and head position on ankle range of motion, ankle passive torque, and passive gastrocnemius tension.

Ankle joint range of motion (ROM) is notably influenced by the position of the hip joint. However, this result remains unexplained. Thus, the aim of this study was to test if the ankle passive torque and gastrocnemius muscle tension are affected by the hip and the head positions. The torque and the muscle shear elastic modulus (measured by elastography to estimate muscle tension) were collected in nine participants during passive ankle dorsiflexions performed in four conditions (by combining hip flexion at 90 or 150°, and head flexed or neutral). Ankle maximum dorsiflexion angle significantly decreased by flexing the hip from 150 to 90° (P < 0.001; mean difference 17.7 ± 2.5°), but no effect of the head position was observed (P > 0.05). Maximal passive torque and shear elastic modulus were higher with the hip flexed at 90° (P < 0.001). During submaximal ROM, no effects of the head and hip positioning (P > 0.05) were found for both torque and shear elastic modulus at a given common ankle angle among conditions. Shifts in maximal ankle angle due to hip angle manipulation are not related neither to changes in passive torque nor tension of the gastrocnemius. Further studies should be addressed to better understand the functional role of peripheral nerves and fasciae in the ankle ROM limits.

Predictors of persistent pain after total knee arthroplasty: a systematic review and meta-analysis.

BACKGROUND: Several studies have identified clinical, psychosocial, patient characteristic, and perioperative variables that are associated with persistent postsurgical pain; however, the relative effect of these variables has yet to be quantified. The aim of the study was to provide a systematic review and meta-analysis of predictor variables associated with persistent pain after total knee arthroplasty (TKA). METHODS: Included studies were required to measure predictor variables prior to or at the time of surgery, include a pain outcome measure at least 3 months post-TKA, and include a statistical analysis of the effect of the predictor variable(s) on the outcome measure. Counts were undertaken of the number of times each predictor was analysed and the number of times it was found to have a significant relationship with persistent pain. Separate meta-analyses were performed to determine the effect size of each predictor on persistent pain. Outcomes from studies implementing uni- and multivariable statistical models were analysed separately. RESULTS: Thirty-two studies involving almost 30 000 patients were included in the review. Preoperative pain was the predictor that most commonly demonstrated a significant relationship with persistent pain across uni- and multivariable analyses. In the meta-analyses of data from univariate models, the largest effect sizes were found for: other pain sites, catastrophizing, and depression. For data from multivariate models, significant effects were evident for: catastrophizing, preoperative pain, mental health, and comorbidities. CONCLUSIONS: Catastrophizing, mental health, preoperative knee pain, and pain at other sites are the strongest independent predictors of persistent pain after TKA.

Static and cyclic stretching: their different effects on the passive torque-angle curve.

The findings of previous research indicate that the passive torque-angle curve may be different according to whether individuals have undertaken cyclic or static stretching. To date, no authors have compared these curves in the same subjects. We hypothesised that static stretching would lead to a constant change in range of motion across torque levels with the shape of the curve being unchanged, while cyclic stretching would change the shape of the curve. To test this hypothesis, eight subjects performed five passive knee extension/flexion cycles on a Biodex dynamometer at 5 degrees s(-1) to 80% of their maximal range of motion before and after a static stretching protocol. The difference in angle between pre and post stretching torque-angle curves was calculated at 11 levels of torque from 0% to 100% of the maximal torque with a 10% increment. The mean change in angle across these 11 torque levels was then calculated. The findings showed that after static stretching a relatively constant mean change of 5.2 degrees was noted across torque levels. In contrast, after cyclic stretching the angle change depended upon the torque level with greater change observed toward the start of the range of motion. The findings indicated that different mechanisms were operating depending upon the type of stretching procedure performed. Changes in muscle resting length and thixotropy were thought to be responsible.

Improvements to Hoang et al.'s method for measuring passive length-tension properties of human gastrocnemius muscle in vivo.

While the passive mechanical properties of a musculo-articular complex can be determined using the relationship between the articular angle and the passive torque developed in resistance to motion, the properties of different structures of the musculo-articular complex cannot be easily assessed. Recently, an elegant method has been proposed to estimate the passive length-tension properties of gastrocnemius muscle-tendon unit (Hoang et al., 2005). In the present paper, two improvements of this method are proposed to decrease the number of parameters required to assess the passive length-tension relationship from 9 to 2. Furthermore, these two parameters have physical meaning as they represent a passive muscle-tendon stiffness index (alpha) and the muscle-tendon slack length (l(0)). alpha and l(0) are relevant clinical parameters to study the chronic effects of aging, training protocols or neuromuscular pathologies on the passive mechanical properties of the muscle-tendon unit. Eight healthy subjects performed passive loading/unloading cycles at 5 degrees /s with knee angle at 6 knee angles to assess the torque-angle relationships and to apply the modified method. Numerical optimization was used to minimize the squared error between the experimental and the modeled relationships. The experiment was performed twice to assess the reliability of alpha and l(0) across days. The results showed that the reliability of the two parameters was good (alpha: ICC=0.82, SEM=6.1m(-1), CV=6.3% and l(0): ICC=0.83, SEM=0.29 cm, CV=0.9%). Using a sensitivity analysis, it was shown that the numerical solution was unique. Overall, the findings may provide increased interest in the method proposed by Hoang et al. (2005).

The effect of angular velocity and cycle on the dissipative properties of the knee during passive cyclic stretching: a matter of viscosity or solid friction.

BACKGROUND: The mechanisms behind changes in mechanical parameters following stretching are not understood clearly. This study assessed the effects of joint angular velocity on the immediate changes in passive musculo-articular properties induced by cyclic stretching allowing an appreciation of viscosity and friction, and their contribution to changes in torque that occur. METHODS: Ten healthy subjects performed five passive knee extension/flexion cycles on a Biodex dynamometer at five preset angular velocities (5-120 deg/s). The passive torque and knee angle were measured, and the potential elastic energy stored during the loading and the dissipation coefficient were calculated. FINDINGS: As the stretching velocity increased, so did stored elastic energy and the dissipation coefficient. The slope of the linear relationship between the dissipation coefficient and the angular velocity was unchanged across repetitions indicating that viscosity was unlikely to be affected. A difference in the y-intercept across repetitions 1 and 5 was indicative of a change in processes associated with solid friction. Electromyographical responses to stretching were low across all joint angular velocities. INTERPRETATION: Torque changes during cyclic motion may primarily involve solid friction which is more indicative of rearrangement/slipping of collagen fibers rather than the redistribution of fluid and its constituents within the muscle. The findings also suggest that it is better to stretch slowly initially to reduce the amount of energy absorption required by tissues, but thereafter higher stretching speeds can be undertaken.

The effects of prior warning and lifting-induced fatigue on trunk muscle and postural responses to sudden loading during manual handling.

This study investigated the effects of warning and lifting-induced fatigue on trunk muscle activity and postural responses to sudden loading. Thirty-one male subjects were subjected to sudden loading of a hand-held box with and without prior warning, before and after either lifting-induced fatigue or light callisthenic exercises. Results showed that warning did not alter the level of trunk muscle activity prior to sudden loading. Following warning, there was a reduction in all muscle and joint onset latencies and the magnitude of hip and knee flexion. Although fatigue did not influence muscle and joint initiation, it did negate the effects that warning had on reducing joint displacement. These findings indicate that warning prior to sudden loading may enhance postural responses, reduce ranges of joint motion and increase stability. However, the benefits of prior warning for reducing ranges of joint motion may not be present when a person is fatigued. Sudden unexpected loading and fatigue arising from manual handling practices in the workplace have been identified as contributing factors to the risk of low back injury. Findings from this study provide information that is important for the design of interventions intended to reduce the incidence of manual handling-related back injuries.

Interventions for the prevention and management of neck/upper extremity musculoskeletal conditions: a systematic review.

Considered from medical, social or economic perspectives, the cost of musculoskeletal injuries experienced in the workplace is substantial, and there is a need to identify the most efficacious interventions for their effective prevention, management and rehabilitation. Previous reviews have highlighted the limited number of studies that focus on upper extremity intervention programmes. The aim of this study was to evaluate the findings of primary, secondary and/or tertiary intervention studies for neck/upper extremity conditions undertaken between 1999 and 2004 and to compare these results with those of previous reviews. Relevant studies were retrieved through the use of a systematic approach to literature searching and evaluated using a standardised tool. Evidence was then classified according to a "pattern of evidence" approach. Studies were categorised into subgroups depending on the type of intervention: mechanical exposure interventions; production systems/organisational culture interventions and modifier interventions. 31 intervention studies met the inclusion criteria. The findings provided evidence to support the use of some mechanical and modifier interventions as approaches for preventing and managing neck/upper extremity musculoskeletal conditions and fibromyalgia. Evidence to support the benefits of production systems/organisational culture interventions was found to be lacking. This review identified no single-dimensional or multi-dimensional strategy for intervention that was considered effective across occupational settings. There is limited information to support the establishment of evidence-based guidelines applicable to a number of industrial sectors.

Effect of verbal instructions on muscle activity and risk of injury to the anterior cruciate ligament during landing.

BACKGROUND: Minimising the likelihood of injury to the anterior cruciate ligament (ACL) during abrupt deceleration requires proper synchrony of the quadriceps and hamstring muscles. However, it is not known whether simple verbal instructions can alter landing muscle activity to protect the knee. OBJECTIVE: To assess the efficacy of verbal instructions to alter landing muscle activity. METHODS: Twenty four athletes landed abruptly in single limb stance. Sagittal plane motion was recorded with an optoelectric device, and ground reaction force and surface electromyographic data were recorded for the rectus femoris, vastus lateralis, biceps femoris, and semimembranosus muscles. Subjects performed 10 landings per condition: normal landing (N); repeat normal landing (R); landing after instruction to increase knee flexion (K); and landing after instruction to recruit hamstring muscles earlier (M). Muscle bursts immediately before landing were analysed relative to initial foot-ground contact (IC). RESULTS: The K condition resulted in significantly (p

Is velocity-specific strength training important in improving functional performance?

A variable considered when designing programs to optimize athletic performance is training velocity. It has been suggested that training at a specific velocity improves strength mainly at that velocity and as velocity deviates from the trained velocity, the less effective training will be. However, the research describing velocity-specific adaptation and the transference of these adaptations to other movement velocities is by no means clear. Compounding the problem in this area is the failure of research to detail the relationship between training velocity and actual movement velocity of a given task or athletic pursuit. In most cases there is a great disparity between training velocity and actual movement velocity. Factors that may better develop and explain velocity-specific adaptation in relation to functional performance are discussed. Developing qualities such as strength, power and rate of force development would appear of greater importance than training at the actual movement velocity of a task. It may be that irrespective of load and limb velocity, the repeated intent to move an isoinertial load as rapidly as possible might be an important stimulus for functional high velocity adaptation. The ability of the nervous system to activate and coordinate agonist, synergist and antagonist activity would seem essential. It was suggested training techniques that simulate the velocity and acceleration profiles associated with the desired functional performance, such as throw or jump training, may optimize functional adaptation. Furthermore combination training that incorporates same session sport specific training with either a heavy load or a mixed training load approach might provide an optimal strategy for promoting intramuscular and intermuscular co-ordination and improving functional performance.

Velocity specificity, combination training and sport specific tasks.

Whether velocity-specific resistance training is important for improving functional sporting performance was investigated by studying the effect of isoinertial training velocity on netball chest pass throwing velocity. Twenty-one female netball players were randomly assigned to a strength-trained group (80% 1RM - average training velocity = .308 m/s), power-trained group (60% 1RM - average training velocity = .398 m/s) and a control group. Resistance training was combined with sport specific motion training for both groups over a ten-week training duration. Pre- and post-training testing revealed that the training velocity associated with the strength-trained group produced significantly greater improvement in mean volume of weight lifted (85kg) and mean power output (13.25 W) as compared to the power and control groups (P< 0.05). The strength-trained and power-trained groups significantly improved netball throw velocity by 12.4% and 8.8% respectively. There was no significant difference between the two groups. The validity of velocity-specific training and subsequent adaptations to improve functional sporting performance appears highly questionable, due to the disparity between training velocity and actual movement velocity (11.38 m x s(-1)) for a given sport specific task such as the netball throw it was proposed that the repeated intent to move an isoinertial load as rapidly as possible coupled with performance of the sport-specific movement promote efficient coordination and activation patterns. Such mechanisms might be more important determinants of sport-specific high velocity adaptation.

Magnitude and decay of stretch-induced enhancement of power output.

There is ample evidence that the pre-stretching of a muscle enhances performance of the subsequent shortening or concentric contraction. The purpose of this study was to investigate this stretch-induced enhancement in terms of the effect of load on the magnitude and decay of the muscle's power output. Instantaneous, mean and peak power outputs were compared between concentric-only and rebound bench press throws at different loads. The maximal strength [1 RM = 84.0 (10.5) kg] of 18 male subjects [21.1 (3.0) years, 87.2 (11.9) kg] was determined using an isoinertial Smith press machine. The results of this study indicate enhancement of concentric motion by prior eccentric muscle action (200-780% enhancement in the first 100 ms). However, the magnitude and temporal characteristics of this enhancement differed across loads. Using a lighter load produced greater initial enhancement (P < 0.05) but the decay of this enhancement was more rapid. The heavier 80% 1 RM loading showed a later time to peak enhancement (80 ms versus 20 ms) and slower decay of the stretch induced augmentation (460 ms versus 260 ms). It is concluded that the degree of stretch-shorten cycle enhancement differs according to the load and the time-dependent characteristics of the motion.

The effect of aircraft control forces on pilot performance during instrument landings in a flight simulator.

BACKGROUND: Pilots may have difficulty controlling aircraft at both high and low force levels due to larger variability in force production at these force levels. The aim of this study was to measure the force variability and landing performance of pilots during an instrument landing in a flight simulator. METHODS: There were 12 pilots who were tested while performing 5 instrument landings in a flight simulator, each of which required different control force inputs. Pilots can produce the least force when pushing the control column to the right, therefore the force levels for the landings were set relative to each pilot's maximum aileron-right force. The force levels for the landings were 90%, 60%, and 30% of maximal aileron-right force, normal force, and 25% of normal force. Variables recorded included electromyographic activity (EMG), aircraft control forces, aircraft attitude, perceived exertion and deviation from glide slope and heading. Multivariate analysis of variance was used to test for differences between landings. RESULTS: Pilots were least accurate in landing performance during the landing at 90% of maximal force (p < 0.05). There was also a trend toward decreased landing performance during the landing at 25% of normal force. Pilots were more variable in force production during the landings at 60% and 90% of maximal force (p < 0.05). CONCLUSION: Pilots are less accurate at performing instrument landings when control forces are high due to the increased variability of force production. The increase in variability at high force levels is most likely associated with motor unit recruitment, rather than rate coding. Aircraft designers need to consider the reduction in pilot performance at high force levels, as well as pilot strength limits when specifying new standards.

Biomechanical behavior of the plantar flexor muscle-tendon unit after an Achilles tendon rupture.

The purpose of this study was to examine the biomechanical behavior of the plantar flexor muscle-tendon unit in subjects who had ruptured their Achilles tendon. Twenty-six men and 14 women volunteered for the study. Eighteen subjects had been treated operatively and 22, nonoperatively. All subjects had ruptured their Achilles tendon more than 1 year before the study, and 28 of the 40 ruptures occurred 5 years or less before the day of testing. A KinCom dynamometer was used to measure ankle joint angle, passive torque, and maximal isometric plantar flexor torque. During a 2-minute passive calf stretch, stiffness and torque relaxation were calculated. Isometric torque and peak passive torque were 17% and 10% greater for the uninvolved versus the involved limb, whereas stiffness and torque relaxation were not different between limbs. The time since injury did not influence the results, nor did the mode of initial treatment, that is, whether the subjects were treated operatively or nonoperatively. These findings suggest that changes in strength and peak passive torque may be chronic adaptations associated with Achilles tendon rupture.

Aircraft control forces and EMG activity: comparison of pilots before and after flying training.

BACKGROUND: Skilled performers in most motor tasks tend to require less force, muscle activity, and co-contraction of agonist and antagonist muscles to complete tasks. There have been two previous studies on muscle activation patterns and applied forces of skilled and novice pilots, but no longitudinal measurements have been made. The aim of this study was to compare the muscle activation patterns of pilots who had recently completed pilot training with those of experienced pilots. A secondary aim of the study was to examine co-contraction of novice and experienced pilots. METHODS: Novice (n = 12) and experienced (n = 9) pilots were tested on an Aermacchi flight simulator. The novice pilots were tested before and after completing pilot training. Pilots performed a set of landings, rolls, and turns, which were administered in a random order. Variables recorded included aircraft attitude, pilot applied forces, and electromyographic (EMG) activity. Discriminant function analysis was used to classify pilots as novice or experienced. RESULTS: Muscle activation patterns of the novice pilots after completion of pilot training were similar to those of experienced pilots. Of the recently graduated pilots, 77% were classified as experienced using discriminant function analysis. The maneuver in which the recently graduated pilots most closely resembled experienced pilots was the left aileron roll. During this maneuver, experienced and recently graduated pilots showed lower levels of co-contraction than novice pilots (p < 0.05). CONCLUSION: The similarities in some muscle activity patterns across qualified pilots, regardless of experience level, may be useful in initiating protective systems such as G-suit inflation.