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.

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.

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 2^nd 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.

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.

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</=0.05) greater knee flexion at IC compared with the other conditions. The M condition did not result in earlier hamstring muscle activity, but instead caused significantly (p</=0.05) earlier rectus femoris onset relative to IC, with a similar trend for the vastus lateralis. As these muscles are ACL antagonists, earlier onset times would be detrimental to the ACL.

CONCLUSIONS

Subjects successfully increased knee flexion during landing following the K condition instruction. However, further research is warranted to establish the efficacy of more extensive lower limb muscle retraining programmes to ensure landings that decrease susceptibility to ACL injury.

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.

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.

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.

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.

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.

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.

Developing explosive power: a comparison of technique and training

The influence of contraction type and movement type on power output of the upper body musculature was investigated across loads of 30-80% 1RM. Twenty seven males (21.9+/-3.1 years, 89.0+/-12.5 kg, 86.32+/-13.66 kg 1RM) of an athletic background but with no weight training experience in the previous six months volunteered for the study. The results were compared using multivariate analysis of variance with repeated measures (p< or =0.05). It was found that the combinations of load, movement and contraction type affected mean and peak power in different capacities. Mean power output for rebound motion was 11.7% greater than concentric only motion. The effect of the rebound was to produce greater peak accelerations (38.5%--mean across loads), greater initial force and peak forces (14.1%--mean across loads) and early termination of the concentric phase. Peak power output was most influenced by the ability to release the bar, the greater mean velocities across all loads (4.4% average velocity and 6.7% peak velocity) attained using such a technique appeared the dominating influence. Loads of 50-70% 1RM were found to maximize mean and peak power. Loading the neuromuscular system to maximize mean or peak power output necessitates an understanding of the force-velocity characteristics of the training movement and the requirements of the individual related to the athletic performance and their training status.

Stretching at the ankle joint: viscoelastic responses to holds and continuous passive motion

PURPOSE

To compare the effect of static holds and continuous passive motion on stiffness and force relaxation of the soft tissue structures resisting ankle joint dorsiflexion.

METHODS

This study used a randomized repeated measures trial design. Twenty-four asymptomatic subjects (15 males and 8 females) with a mean age of 26 yr participated. A Kin-Com dynamometer was used to measure the stiffness and force relaxation response of tissues about the ankle joint in response to a plantar flexor stretch. A comparison was made of the response for a 1 x 60-s hold, 2 x 30-s holds, 4 x 15-s holds, and continuous passive motion for 60 s. All subjects undertook all conditions. The main outcome measures were 1) stiffness at the ankle joint as it moved to 80% of the maximum range of dorsiflexion, and 2) the decrease in force at 80% of the maximum range of motion of the ankle joint.

RESULTS

Stiffness was decreased significantly (P < 0.05) for the continuous passive motion condition only. The mean magnitude of the decrease in stiffness was 16%. Across hold times, force decreased significantly (P < 0.05). Bonferonni contrasts indicated that there was a significant difference (P < 0.05) between the continuous passive motion condition and all other hold conditions. There were no significant differences (P > 0.05) between the 4 x 15-s, 2 x 30-s, and 1 x 60-s holds. The magnitude of the decline in force was 10.5%, 21.5%, 21.7%, and 19% for the 0-, 15-, 30-, and 60-s holds, respectively. The greatest decreases in tension were achieved in the first 20 s of a hold.

CONCLUSION

If decreasing stiffness is a key aim of a stretching program, the findings indicate that continuous motion is more effective than holds. In contrast, if relaxation of peak tension is the main aim, then holds are most effective.

Aircraft control forces and EMG activity in a C-130 Hercules during strength-critical maneuvers

BACKGROUND

The force levels required to operate aircraft controls should be readily generated by pilots, without undue fatigue or exertion. However, maximum pilot applied forces, as specified in aircraft design standards, were empirically derived from the subjective comments of test pilots, and may not be applicable for the majority of pilots. Further, experienced RNZAF Hercules flying instructors have indicated that endurance and fatigue are problems for Hercules pilots. The aim of this study was to quantify aircraft control forces during emergency maneuvers in a Hercules aircraft and compare these forces with design standards. In addition, EMG data were recorded as an indicator of muscle fatigue during flight.

METHODS

Six subjects were tested in a C-130 Hercules aircraft. The maneuvers performed were low-level dynamic flight, one engine-off straight-and-level flight, and a two-engines-off simulated approach. The variables recorded were pilot-applied forces and EMG activity.

RESULTS

Left rudder pedal force and vastus lateralis activity were both significantly greater during engine-off maneuvers than during low-level dynamic flight (p < 0.05). Maximum aircraft control forces for all controls were within 10% of the design standards. The mean EMG activity across all muscles and maneuvers was 26% MVC, with a peak of 61% MVC in vastus lateralis during the two-engine-off approach. The median frequency of the vastus lateralis EMG signal decreased 13.0% and 16.0% for the one engine-off and two-engine-off maneuvers, respectively.

CONCLUSION

The forces required to fly a Hercules aircraft during emergency maneuvers are similar to the aircraft design standards. However, the levels of vastus lateralis muscle activation observed during the engine-off maneuvers can be sustained for approximately 1 min only. Thus, if two engines fail more than 1 min before landing, pilots may have to alternate control of the aircraft to share the workload and enable the aircraft to land safely.

The role of maximal strength and load on initial power production

PURPOSE

The influence of maximal strength, as measured by the maximal load lifted for one repetition (1RM), on power production in the initial 200 ms of the concentric phase for both rebound and nonrebound movements was investigated. We also investigated the effect of external load upon this relationship.

METHODS

Twenty-seven male subjects (21.9 +/- 3.1 yr, 89.0 +/- 12.5 kg) were separated by previously determined bench press IRM into high (100.88 +/- 7.24 kg) and low (72 +/- 6.61 kg) RM groups. Concentric only bench presses and rebound bench presses were compared between and within groups to note the effect of RM across external loads of 40%, 60%, and 80% 1RM, on instantaneous, mean, and peak power output.

RESULTS

The results of this study clearly indicated the enhancement of concentric motion by prior eccentric muscle action (336-1332% enhancement in the first 20 ms). Possessing a high RM augmented power production in the initial 200 ms of stretch-shorten cycle activity, across all the external resistances tested (P < 0.05). The temporal characteristics of this enhancement, however, differed across loads. That is, 80% IRM loading showed a later time to peak enhancement (80 ms vs 20 ms). Interestingly, the influence of RM on concentric only motion in the initial 200 ms across the external resistances tested was found to be nonsignificant.

CONCLUSIONS

The results suggest that the role of maximal strength during initial power production between concentric and stretch-shorten cycle activity differs, which has important implications for the training of athletes.

Decreasing landing forces: effect of instruction

OBJECTIVE

To examine the effects of instructions related to joint kinematics, auditory stimuli, and imagery on lowering the vertical ground reaction forces associated with landing from a jump.

STUDY DESIGN

Randomised controlled trial.

SETTING

A laboratory in an educational institution.

SUBJECTS

Eighty asymptomatic subjects (27 men) with a mean age of 24 years.

INTERVENTION

Subjects were randomly assigned to the following groups: (1) instruction (limb position instructions); (2) auditory cue (listen to impact sounds); (3) imagery (metaphorical); (4) control. Subjects were required to jump from a box 300 mm in height and land on a force plate. Measures of the ground reaction force were recorded before and after the intervention.

MAIN OUTCOME MEASURE

The peak vertical ground reaction force recorded at footstrike.

RESULTS

The peak vertical ground reaction forces in the technical instruction and auditory groups were significantly less than those of the control group. There was no significant difference between the auditory and technical instruction groups. There was no significant difference between the imagery and control groups.

CONCLUSIONS

When an aim of a rehabilitation programme is to minimise forces on the lower limb during landing type activities, the findings support the use of instructions related to kinematics as well as instructions that draw the patient's attention to the sound at impact.

Aircraft control forces and EMG activity: comparison of novice and experienced pilots during simulated rolls, loops and turns

BACKGROUND

Flying an aircraft requires a considerable degree of coordination, particularly during aerobatic activities such as rolls, loops and turns. Only one previous study has examined the magnitude of muscle activity required to fly an aircraft, and that was restricted to takeoff and landing maneuvers. The aim of this study was to examine the phasing of muscle activation and control forces of novice and experienced pilots during more complex simulated flight maneuvers.

METHODS

There were 12 experienced and 9 novice pilots who were tested on an Aermacchi flight simulator while performing a randomized set of rolling, looping, and turning maneuvers. Four different runaway trim settings were used to increase the difficulty of the turns (elevator-up, elevator-down, aileron-left, and aileron-right). Variables recorded included aircraft attitude, pilot applied forces, and electromyographic (EMG) activity. Discriminant function analysis was used to distinguish between novice and experienced pilots.

RESULTS

Over all maneuvers, 70% of pilots were correctly classified as novice or experienced. Better levels of classification were achieved when maneuvers were analyzed individually (67-91%), although the maneuvers that required the greatest force application, elevator-up turns, were unable to discriminate between novice and experienced pilots. There were no differences in the phasing of muscle activity between experienced and novice pilots. The only consistent difference in EMG activity between novice and experienced pilots was the reduced EMG activity in the wrist extensors of experienced pilots (p < 0.05). The increased wrist extensor activity of the novice pilots is indicative of a distal control strategy, whereby distal muscles with smaller motor units are used to perform a task that requires precise control. Muscle activity sensors could be used to detect the onset of high G maneuvers prior to any change in aircraft attitude and control G-suit inflation accordingly.

Aircraft control forces and EMG activity in a UH-1H Iroquois helicopter during emergency maneuvers

BACKGROUND

Some air forces are concerned with the adequacy of existing pilot selection standards in respect to pilot strength. Some studies have provided evidence that a large number of pilots may not be able to match the control force levels specified in both military and civilian aircraft design standards. However, both sets of design standards have been based on the subjective comments of test pilots and may not, therefore, be applicable for the majority of pilots. The aim of this study was to quantify aircraft control forces during emergency maneuvers in an Iroquois helicopter and compare these forces with design standards. The examination of muscle activation patterns of pilots during maneuvers, when normalized, can provide additional information on the relative activation levels that pilots are using to produce the aircraft control forces.

METHODS

Six pilots were tested in a UH-1 H Iroquois helicopter. The maneuvers were three engine-out landings and a hydraulics-off landing. The variables recorded were pilot applied forces and EMG activity. Multivariate analysis of variance was used to test for differences between maneuvers.

RESULTS

The greatest cyclic and upward collective control forces were observed during constant attitude and variable flare engine-out landings. The greatest downward collective forces were observed during hydraulics-off landing. Greater levels of muscle activation were consistently observed during hydraulics-off landing than during the engine-out landings. Control forces consistently exceeded military design standards for cyclic and collective controls, however muscle activity levels were sub-maximal for all maneuvers.

CONCLUSION

Comparisons between existing aircraft control-force design standards and pilot strength may overestimate the number of pilots who are able to produce sufficient force to fly the aircraft. Despite the high control forces observed, all pilots tested were able to successfully maneuver the helicopter without requiring a maximal muscular effort.

Aircraft control forces and EMG activity in a UH-1H Iroquois helicopter during routine maneuvers

BACKGROUND

Flying a helicopter requires greater coordination than flying a fixed-wing aircraft, because the pilot is required to apply force simultaneously to three controls: the cyclic, collective, and pedals. There has been one study of pilot applied forces during helicopter flight, but this investigation did not examine muscle activity patterns. The aim of this study was to examine the muscle activation patterns and control forces of helicopter pilots during routine maneuvers.

METHODS

Six pilots were tested in a UH-1 h Iroquois helicopter. The maneuvers involved hovering, winching, under-slung loads, a constant rate turn, and a high-speed valley turn. Variables recorded were pilot applied forces and electromyographic activity (EMG). Multivariate analysis of variance was used to test for differences between maneuvers.

RESULTS

Significant differences between the maximum forces recorded from each control across all maneuvers were recorded (p < 0.05). The greatest pilot applied forces were recorded from the pedals. No muscles were activated more than 25% of a maximum voluntary contraction for any maneuver. The greatest magnitude of EMG activity was recorded from vastus lateralis during high-speed valley turns. There were significant differences between the EMG activity of left triceps, right triceps, and right deltoid for some maneuvers (p < 0.05).

CONCLUSION

The control forces required to fly a helicopter during routine maneuvers are small. The levels of muscle activation associated with pilot applied forces are also low, but are similar to those reported during routine maneuvers in a fast-jet flight simulator.

Aircraft control forces and EMG activity: comparison of novice and experienced pilots during simulated take-off and landing

BACKGROUND

Flying an aircraft requires a considerable degree of coordination, particularly during activities such as takeoff and landing. No studies have examined the magnitude and phasing of muscle activity required to fly an aircraft. The aim of this study was to examine the muscle activation patterns and control forces of novice and experienced pilots during simulated flight.

METHODS

Twelve experienced and nine novice pilots were tested on an Aermacchi flight simulator while performing a randomized set of take-off and landing maneuvers. Four different runaway trim settings were used to increase the difficulty of the landings (elevator-up, elevator-down, aileron-left, and aileron-right). Variables recorded included aircraft attitude, pilot applied forces, and electromyographic (EMG) activity. Discriminant function analysis was used to distinguish between novice and experienced pilots.

RESULTS

Across all landings, wrist flexors and wrist extensors were the predominant muscles used, with EMG activity consistently around 20-30% maximum voluntary contraction (MVC). In respect to differences in EMG activity between novice and experienced pilots, novices had significantly more activity in wrist extensors during all landings. In contrast, experienced pilots had consistently more vastus lateralis activity for all landings than did novice pilots. Over all landings and take-off, 89.5% of pilots were correctly classified as novice or experienced. When the maneuvers were analyzed individually, normal, elevator-down, and aileron-left landings were the most accurate maneuvers for pilot prediction. EMG and force variables were more important than aircraft attitude in discriminating between novice and experienced pilots (83%, 79%, and 65%, respectively).

CONCLUSION

The consistency of the finding that EMG activity and control forces are accurate discriminators of pilot experience is indicative of underlying differences in neuromuscular control strategies between novice and experienced pilots.

Effects of instruction in jumping technique and experience jumping on ground reaction forces

STUDY DESIGN

Randomized, controlled trial.

OBJECTIVE

To determine the roles that augmented feedback from instruction in jumping technique and sensory feedback from experience jumping play in assisting individuals to land softly from a jump.

BACKGROUND

Jumping and landing activities play a major role in many sports and daily activities. Feedback may assist individuals in decreasing landing forces and thus reduce the chances of sustaining an injury.

METHODS AND MEASURES

Nonimpaired subjects (n = 91) were randomly assigned to either an augmented or sensory feedback condition. All subjects were asked to jump from a box 300 mm in height and land as softly as possible on a force plate. Pre-intervention ground reaction forces (GRF) were recorded. Subjects in the augmented feedback condition were then given instructions to focus on hip and knee joint motion as well as a forefoot landing technique for their next jump. Subjects in the sensory feedback condition were asked to use the experience of their first jump to land softly for their next jump. Post-intervention GRFs were recorded and all GRFs were expressed as a multiple of body weight.

RESULTS

Those in the augmented condition significantly reduced their GRF scores from pre-(mean = 4.53 +/- 1.51) to post-(mean = 3.57 +/- 1.10) jump, whereas those in the sensory condition did not (mean pre GRF = 4.51 +/- 1.77; mean post GRF = 4.33 +/- 1.54).

CONCLUSIONS

High ground reaction forces may be a precipitating factor associated with an injury, where the site of tissue damage would benefit from decreased forces. These findings support the use of instructions related to joint motion to reduce landing forces.

Normative data of vertical ground reaction forces during landing from a jump

This technical report provides normative data of vertical ground reaction forces (GRFs) associated with landing from a jump. Subjects were 234 adolescents (mean age: 16 years) who were categorised by gender, activity level and type of sport played. Subjects jumped from a box 0.3 metres high to land on a force plate. Results showed that there were no significant differences (p>0.05) across gender, activity levels, and type of sport played. Across all subjects, the mean peak vertical GRF was 4.5 bodyweights (SD: 1.7). In regard to gender, mean peak vertical GRFs were 4.6 (SD: 1.7) and 4.2 (SD: 1.4) for males and females respectively. The mean peak vertical GRF for subjects involved in recreational sport 1-3 times per week was 4.4 bodyweights (SD: 1.7), while the mean for those playing competitive sport 4-7 times per week was 4.5 bodyweights (SD: 1.7). The mean peak vertical GRF for subjects participating in sports involving jumping and landing activities was 4.6 bodyweights (SD: 1.8) as compared to 4.4 bodyweights (SD: 1.5) for subjects in sports that did not involve jumping activities.

Trunk proprioception: enhancement through lumbar bracing

OBJECTIVES

To examine the effects of a neoprene lumbar brace on the proprioceptive ability of subjects without pathology and to determine whether those with poorer proprioception were more affected by the brace.

STUDY DESIGN

Randomized 2 x 2 Latin square cross-over design.

SETTING

Laboratory in an educational institution.

SUBJECTS

Forty asymptomatic subjects matched by gender, age, weight, and height.

METHOD

Blindfolded subjects performed a position matching task in which they flexed the trunk in the sagittal plane. Six positions across the range of motion were examined. Angular data were recorded by a lumbar motion monitor secured by straps to the subject's trunk.

MAIN OUTCOME MEASURE

Absolute, constant, and variable errors in braced and unbraced conditions.

RESULTS

The mean absolute, constant, and variable errors were 3.6 degrees, .45 degrees, and 4.4 degrees, respectively. Absolute, constant, and variable errors were significantly decreased when wearing a brace. However, the magnitude of the decreases were small (<1.0 degrees) for all errors when wearing a brace. The high error group's absolute error improved significantly (p < .05), from 6.0 degrees when unbraced to 4.0 degrees when braced. In contrast, absolute error measurements for subjects in the low error group were unchanged, with an error of 2.0 degrees when unbraced and 2.3 degrees when braced.

CONCLUSIONS

The findings suggest that a neoprene lumbar brace improves the somatosensory information received by the central nervous system and results in less error in trunk positioning. Persons with less ability to match trunk position will benefit more from wearing a neoprene brace than will those who are already adept at the task.

Effect of passive stretching and jogging on the series elastic muscle stiffness and range of motion of the ankle joint

OBJECTIVE

To determine the effect of stretching and jogging on the series elastic muscle stiffness of the plantar flexors and on the range of dorsiflexion at the ankle joint.

METHODS

24 healthy subjects participated in this study. Each subject undertook all of the following protocols, in random order: (1) stretching protocol: five 30 s static stretches with 30 s rest between stretches; (2) aerobic jogging protocol: subjects ran on a treadmill for 10 min at 60% of their maximum age predicted heart rate; (3) combined protocol: subjects ran first and then stretched. A damped oscillation technique was used to measure the series elastic stiffness of the plantar flexors. Dorsiflexion of the ankle was assessed with a weights and pulley system that moved the ankle joint from a neutral position into dorsiflexion passively. Electromyography was used to monitor the activity of the plantar and dorsiflexors during these procedures. The statistical analysis of these data involved an analysis of covariance.

RESULTS

For decreasing series elastic muscle stiffness running was more effective than stretching (P < 0.05). In contrast, the results for range of motion showed that the combination protocol and the stretching only protocol were more effective than the running only protocol (P < 0.05) for increasing dorsiflexion range of motion at the ankle.

CONCLUSIONS

Both jogging and static stretching exercises appear to be beneficial to individuals participating in sporting activities.

Verbal encouragement: effects on maximum effort voluntary muscle action

OBJECTIVE

To examine the effects of verbal encouragement on the peak force of the elbow flexors during an isometric muscle action.

METHODS

A crossover design whereby 20 subjects were divided into 10 2 x 2 Latin squares was undertaken. Peak forces were measured on a Kin-Com dynamometer, and electromyographic (EMG) activity was also recorded from the biceps brachii. All subjects completed trials with and without verbal encouragement.

RESULTS

Mean peak force increased (P < 0.05) from 296 to 311 N (5%) when verbal encouragement was presented. A spectral analysis of the EMG activity showed no changes (P > 0.05) to the median frequency in the condition where verbal encouragement was present.

CONCLUSIONS

These findings have ramifications for training and exercise therapy. An awareness of the effects of verbal encouragement is important when motivating athletes and patients to attain maximum performance during exercise.

Swelling of the knee joint: effects of exercise on quadriceps muscle strength

OBJECTIVE

To investigate the effects of excessive fluid in the knee joint on the performance of the quadriceps muscles and to determine whether quadriceps muscle performance can be altered by exercising the swollen joint.

DESIGN AND SETTING

A before-after trial design was used, and the procedures were performed in a laboratory setting.

SUBJECTS

A random sample of 27 adult men with no musculoskeletal problems was divided into intervention and control groups.

INTERVENTION

First, in all groups, torque generated by the quadriceps muscle was examined by isokinetic muscle testing undertaken at a joint angular velocity of 120 degrees/sec over a range of motion from 5 degrees to 80 degrees flexion. After this initial test, in group 1, 60mL saline and dextrose was injected into the knee joint and subjects repeated the maximal effort procedure. Subjects then performed submaximal exercise for 3 to 4 minutes, after which maximal effort testing was undertaken again. In group 2, subjects received no injection of fluid, undertook 2 maximum effort tests, then performed submaximal exercise for 3 to 4 minutes, after which maximum effort testing was undertaken again. In group 3 (control group), subjects undertook three maximum effort tests over a time period similar to that for the other groups.

MAIN OUTCOME MEASURE

Quadriceps muscle torque generated at 60 degrees from full knee extension.

RESULTS

Torque decreased (p < .05) 30% immediately after the injection of fluid. However, torque returned to preinjection levels after submaximal exercise (p > .05). These findings were related to joint capsule compliance and fluid movement. No significant changes (p > .05) in torque were observed for the other two groups.

CONCLUSION

Submaximal exercise of swollen knee joints can decrease artificially induced quadriceps muscle inhibition. These findings may have implications for patients with perennial effusions who at times undertake gait activities.

Quadriceps muscle training in a restricted range of motion: implications for anterior cruciate ligament deficiency

This study examined the transferability of strength gains associated with training in a limited range of motion, and at a specific joint angular velocity, to a different part of the range of motion. Work was assessed in control (N = 14) and experimental (N = 14) groups that performed baseline tests on a Kin-Com dynamometer at 1.05, 2.09, and 3.14 rad/sec, over a range of motion from 90 degrees flexion to full extension. The experimental group then underwent training consisting of three sets of eight maximum-effort knee extensions on a Kin-Com dynamometer at a joint angular velocity of 2.09 rad/sec, three times per week for 8 weeks. The range of motion at which they trained was 90 degrees to 45 degrees. After training, baseline tests were repeated in both groups. The findings showed that the work done by the quadriceps muscles of the experimental group increased significantly (p < .05) in the training range of motion across all joint angular velocities. In the untrained range of motion, the work done by the experimental group increased significantly (p < .05) only at the training angular velocity of 2.09 rad/sec. These findings provide evidence that training in a range of motion in which anterior shear forces are low can lead to changes in strength in the range of motion in which anterior shear forces are high. Hence, such exercise is of potential benefit to the anterior cruciate ligament-deficient individual.

Knee bracing: effects of proprioception

OBJECTIVE

To examine the effects of a knee sleeve type brace on the proprioceptive ability of subjects with normal knees during a dynamic tracking task.

DESIGN

A 2 X 2 Latin square cross over design; in each Latin square, subjects were matched for age and gender.

SETTING

An institution focused on clinical education.

PARTICIPANTS

Twenty subjects with no musculoskeletal or neurological conditions.

INTERVENTIONS

Each subject performed a tracking task on a Kin-Com dynamometer. Angle and force data from the Kin-Com and angle data from an electrogoniometer were sampled at 100Hz using a data acquisition program on a PC computer. The subjects were blindfolded and the limb attached to the Kin-Com was moved passively by the dynamometer. Subjects were instructed to follow the movement as closely as possible with the other limb (the tracking limb). Subject performed two trials, one without knee bracing and another that involved the application of a brace to the tracking limb.

OUTCOME MEASURE

The magnitude of the error in tracking was established by taking the difference of the active and passively moving limbs and calculating the root mean square (RMS) of the difference.

RESULTS

The findings showed that there was an improvement of 11% in tracking when subjects wore the knee brace (p < .05).

CONCLUSION

Alterations in proprioception as a result of bracing may be partly responsible for the improvement in knee injury statistics reported in some studies.

Knee joint effusion and proprioception

The purpose of this study was to examine the effects of excessive fluid in the knee joint on proprioception. Twenty healthy subjects with no knee pathology participated in this study. Subjects were randomly assigned to control and experimental groups. Baseline measurements of subjects performing a tracking task were then recorded. Specifically, one knee joint was moved passively by a dynamometer through a range of motion from approximately 90 degrees flexion to 10 degrees from full extension at a joint angular velocity of 60 degrees/sec. Subjects were blindfolded and required to track the passively moving joint as accurately as possible for a period of 1.25 minutes with the opposite limb. An electrogoniometer was used to monitor the motion of the active tracking limb. Ninety mL of a solution of saline and dextrose were injected into the knee joint cavity of the experimental subjects, and they repeated the tracking task. After a 5-minute rest, the control group subjects also repeated the task. The results indicated that the injection of fluid did not change the subjects' error in tracking the passively moving limb (p > 0.05). No change in the error associated with tracking was observed for the control group (p > 0.05). It is suggested that the effects of long-term effusions and the nature of the inflammatory fluid might be more responsible for the loss of proprioception observed in some clinical conditions.

Kinematic and kinetic parameters associated with running in different shoes

The characteristics of the midsole were examined in four pairs of running shoes by a materials test. The variables of interest were the peak acceleration, time to peak acceleration and the kinetic energy absorbed. Ten subjects then ran at a recreational jogging pace (3.5 ms-1) barefoot and in the shoes. An accelerometer secured to the lower tibia was used to measure the peak acceleration and time to peak acceleration associated with footstrike. Subjects were also videoed and a kinematic analysis was undertaken at the knee and ankle joints. The results from the materials test showed that the shoes differed in their midsole characteristics, however, no significant differences (P > 0.05) were observed in the peak acceleration and time to peak acceleration during running in shoes. These variables were significantly greater in the barefoot running condition (P < 0.05), as compared with running in shoes. Small and subtle kinematic differences were observed between the barefoot and shoe conditions. It appears that the differences observed between the shoes in the materials test were not sufficient to elicit the kinematic changes observed between the barefoot and shoe conditions. It is suggested that runners operate within a 'kinetic bandwidth' when responding to impact stresses.

Knee effusion and quadriceps muscle strength

Ten healthy subjects with no musculoskeletal problems were tested using a computerized exercise dynamometer. Quadriceps femoris concentric performance was examined during maximal effort isokinetic knee extension at joint angular velocities of 2.09 and 4.18 rad s(-1). A saline and dextrose solution was injected into the knee joint cavity in 30-ml increments, and peak torque and power tests were undertaken with knee effusions of 0, 30, 60, and 90 ml. A protocol which included and excluded a local skin anaesthetic and submaximal exercise prior to the maximal effort test was also undertaken. The results showed that quadriceps peak torque and power were not significantly affected by the amount of knee effusion at either joint angular velocity when submaximal exercise was performed prior to the maximal effort test. However, peak torques were significantly decreased during isokinetic muscle action without prior submaximal muscle work. It was suggested that these findings may be related to fluid movement in the knee joint compartments, the compliance of the joint capsule, and the location that fluid was injected into the joint cavity. Joint swelling is a common symptom of individuals with osteoarthritis and rheumatoid arthritis, as well as those suffering acute joint trauma. This study has extended previous work on joint swelling by examining quadriceps function during joint movement, thus moreeffectivelysimulating joint and muscle activity which occursduring functional activities. Patients with knee joint swelling are thought to experience greater difficulty undertaking quadriceps exercises, and will not perform these exercises effectively until swelling in the joint is reduced. The current study provides some evidence to suggest that a moderate amount of swelling does not impair performance. Assuming that patients do not have other symptoms that contraindicate exercise, they can be encouraged to do more active muscle work.

Landing characteristics in subjects with normal and anterior cruciate ligament deficient knee joints

Sixteen subjects with arthroscopically verified anterior cruciate ligament (ACL) deficiency and 16 subjects without knee problems participated in this study. The functional ability of the ACL-deficient subjects was assessed with the Noyes knee rating system. Each subject completed a landing task in which they hopped from a box 300mm in height to land on one leg. Vertical ground reaction forces and anterior tibial accelerations were recorded, while electrogoniometers measured angular displacement at the knee and ankle joints. Electromyographic (EMG) signals from the vasti lateralis and lateral hamstrings were also recorded. The active stiffness of the hamstring muscles was also assessed in the ACL-deficient subjects. No significant differences (p > 0.05) were observed between the ACL-deficient group and the normal knee group for the landing task. Nor were any significant correlations (p > 0.05) observed between the kinematic, electromyographic variables and the functional ability of the ACL-deficient subjects. However, the active stiffness of the hamstring muscles was positively correlated with functional ability (r = 0.73, p < 0.05), whereas it was negatively related (r = -0.83, p < 0.05) to the magnitude of the EMG activity observed during the landing task. These findings suggest that there is an interplay between the stiffness characteristics of the hamstring muscles and their activation by central processes. It was apparent that not all ACL-deficient subjects take on a landing strategy to minimize stress to their knee joints.

Frequency analysis of the EMG from the quadriceps of anterior cruciate ligament deficient individuals

A bilateral comparison of the peak torque generated by the quadriceps muscles during isokinetic muscle action at a joint angular velocity of 180 deg/sec was undertaken in 17 subjects with chronic anterior cruciate ligament (ACL) deficiency. The results allowed subjects to be separated into minimal and maximal deficit groups. A frequency analysis of the electromyographic signals of the vasti lateralis obtained during the peak torque tests was then undertaken. The results showed that the median frequency of the ACL deficient limb in the maximal deficit group was significantly (p < 0.05) decreased compared to the median frequency of the uninvolved limb and both limbs of the minimal deficit group. These results suggested that type II muscle fibre atrophy had occurred. The frequency analysis of EMG may provide a noninvasive technique of measuring relative fibre atrophy differences between legs.

Stiffness of the hamstring muscles and its relationship to function in anterior cruciate ligament deficient individuals

The relationship between hamstring muscle stiffness and the functional ability level of 17 subjects with complete anterior cruciate ligament rupture confirmed at arthroscopy was examined. The hamstring muscles were modelled as a single degree of freedom mass spring system with a damping component. Using this model the stiffness of these muscles was examined at 30, 45, and 60% of a maximum voluntary isometric muscle action. The functional ability of the subjects, attained using the Noyes knee rating system, was then correlated to muscle stiffness measures. Positive correlations of 0.71, 0.72, and 0.62 at the three respective muscle loading levels were observed. These findings suggested that hamstring muscle stiffness may have an important role to play in the functional ability of subjects with anterior cruciate ligament deficiency. At this time there is no single effective treatment for all individuals with anterior cruciate ligament deficiency. Those individuals who undergo a conservative management programme are usually treated with hamstring muscle exercises for improving knee flexion strength. The current study provides evidence that hamstring exercises may alter other properties of muscles, such as their active stiffness, which in turn may influence the functional ability of the anterior cruciate ligament deficient individual.

Quadriceps strength deficit associated with rectus fernoris rupture: a case report

We report a case of rectus femoris rupture of the quadriceps muscles. Isokinetic muscle testing was undertaken at joint angular velocities of 60, 120, 180, 240, and 300 deg s(-1) to establish the knee extensor muscle strength deficits associated with this condition. The mean strength deficit over these joint angular velocities was 16.6%.

Important features associated with acute anterior cruciate ligament injury

The mechanism of injury and the signs and symptoms associated with initial injury to the anterior cruciate ligament were investigated in 23 subjects. The subjects had injured only their anterior cruciate ligament with no other clinically definable laxity to other major ligamentous structures. The results showed that 70% of subjects had injured their anterior cruciate ligament at footstrike during noncontact situations. In 53% of these subjects the mechanism of injury was internal rotation of the tibia with the knee in slight flexion. A shifting sensation occurring between the tibia and femur was noted by 61% of subjects, while 30% recalled a crack or popping sound at the time of injury. Only 17% of subjects could continue in sports activity immediately following the injury, all with difficulty.