The Effect of Wave Motion Intensities on Performance in a Simulated Search and Rescue Task and the Concurrent Demands of Maintaining Balance.

OBJECTIVE: The purpose of this study was to examine how intensity of wave motions affects the performance of a simulated maritime search and rescue (SAR) task. BACKGROUND: Maritime SAR is a critical maritime occupation; however, the effect of wave motion intensity on worker performance is unknown. METHODS: Twenty-four participants (12 male, 12 female) performed a simulated search and rescue task on a six-degree-of-freedom motion platform in two conditions that differed in motion intensity (low and high). Task performance, electromyography (EMG), and number of compensatory steps taken by the individual were examined. RESULTS: As magnitude of simulated motion increased, performance in the SAR task decreased, and was accompanied by increases in lower limb muscle activation and number of steps taken. CONCLUSIONS: Performance of an SAR task and balance control may be impeded by high-magnitude vessel motions. APPLICATION: This research has the potential to be used by maritime engineers, occupational health and safety professionals, and ergonomists to improve worker safety and performance for SAR operators.

Higher Quadriceps Roller Massage Forces Do Not Amplify Range-of-Motion Increases nor Impair Strength and Jump Performance.

Grabow, L, Young, JD, Alcock, LR, Quigley, PJ, Byrne, JM, Granacher, U, Skarabot, J, and Behm, DG. Higher quadriceps roller massage forces do not amplify range-of-motion increases nor impair strength and jump performance. J Strength Cond Res 32(11): 3059-3069, 2018-Roller massage (RM) has been reported to increase range of motion (ROM) without subsequent performance decrements. However, the effects of different rolling forces have not been examined. The purpose of this study was to compare the effects of sham (RMsham), moderate (RMmod), and high (RMhigh) RM forces, calculated relative to the individuals' pain perception, on ROM, strength, and jump parameters. Sixteen healthy individuals (27 ± 4 years) participated in this study. The intervention involved three 60-second quadriceps RM bouts with RMlow (3.9/10 ± 0.64 rating of perceived pain [RPP]), RMmod (6.2/10 ± 0.64 RPP), and RMhigh (8.2/10 ± 0.44 RPP) pain conditions, respectively. A within-subject design was used to assess dependent variables (active and passive knee flexion ROM, single-leg drop jump [DJ] height, DJ contact time, DJ performance index, maximum voluntary isometric contraction [MVIC] force, and force produced in the first 200 milliseconds [F200] of the knee extensors and flexors). A 2-way repeated measures analysis of variance showed a main effect of testing time in active (p < 0.001, d = 2.54) and passive (p < 0.001, d = 3.22) ROM. Independent of the RM forces, active and passive ROM increased by 7.0% (p = 0.03, d = 2.25) and 15.4% (p < 0.001, d = 3.73) from premeasure to postmeasure, respectively. Drop jump and MVIC parameters were unaffected from pretest to posttest (p > 0.05, d = 0.33-0.84). Roller massage can be efficiently used to increase ROM without substantial pain and without subsequent performance impairments.

Barefoot running does not affect simple reaction time: an exploratory study.

BACKGROUND: Converging evidence comparing barefoot (BF) and shod (SH) running highlights differences in foot-strike patterns and somatosensory feedback, among others. Anecdotal evidence from SH runners attempting BF running suggests a greater attentional demand may be experienced during BF running. However, little work to date has examined whether there is an attentional cost of BF versus SH running. OBJECTIVE: This exploratory study aimed to examine whether an acute bout of BF running would impact simple reaction time (SRT) compared to SH running, in a sample of runners naïve to BF running. METHODS: Eight male distance runners completed SRT testing during 10 min of BF or SH treadmill running at 70% maximal aerobic speed (17.9 ± 1.4 km h-1). To test SRT, participants were required to press a hand-held button in response to the flash of a light bulb placed in the center of their visual field. SRT was tested at 1-minute intervals during running. BF and SH conditions were completed in a pseudo-randomized and counterbalanced crossover fashion. SRT was defined as the time elapsed between the light bulb flash and the button press. SRT errors were also recorded and were defined as the number of trials in which a button press was not recorded in response to the light bulb flash. RESULTS: Overall, SRT later in the exercise bouts showed a statistically significant increase compared to earlier (p < 0.05). Statistically significant increases in SRT were present at 7 min versus 5 min (0.29 ± 0.02 s vs. 0.27 ± 0.02 s, p < 0.05) and at 9 min versus 2 min (0.29 ± 0.03 s vs. 0.27 ± 0.03 s, p < 0.05). However, BF running did not influence this increase in SRT (p > 0.05) or the number of SRT errors (17.6 ± 6.6 trials vs. 17.0 ± 13.0 trials, p > 0.05). DISCUSSION: In a sample of distance runners naïve to BF running, there was no statistically significant difference in SRT or SRT errors during acute bouts of BF and SH running. We interpret these results to mean that BF running does not have a greater attentional cost compared to SH running during a SRT task throughout treadmill running. Literature suggests that stride-to-stride gait modulation during running may occur predominately via mechanisms that preclude conscious perception, thus potentially attenuating effects of increased somatosensory feedback experienced during BF running. Future research should explore the present experimental paradigm in a larger sample using over-ground running trials, as well as employing different tests of attention.

Therapists' cues influence lower limb muscle activation and kinematics during gait training in subacute stroke.

PURPOSE: Symmetrical gait is a key goal of rehabilitation post-stroke. Therapists employ techniques such as verbal instruction and haptic cues to increase activation of paretic muscles. We examined whether verbal or tactile cueing altered spatiotemporal gait parameters, kinematics and electromyography (EMG) of lower limb muscles on the more-affected side within a training session. MATERIALS AND METHODS: Patients (n = 10) were recruited from rehabilitation services (<9 months post-stroke). Tactile (to the hip muscles) or verbal cues were provided on two testing days, 7-10 days apart (randomized order). Gait and angular kinematics were recorded using a Vicon motion capture system and muscle activation using EMG; at baseline (PRE), during the cue, directly afterwards without a cue (POST) and 20 min later without a cue (RETEST). RESULTS: Both verbal and tactile cueing significantly increased muscle activity in paretic muscles but with no immediate effect on step length asymmetry. Tactile cues, more than verbal, temporarily altered gait speed, cadence and time in double support. Verbal cues caused more robust increases in muscle activation of vastus lateralis at weight acceptance and medial gastrocnemius activity from toe off to midswing. CONCLUSIONS: Within a treatment session, tactile cues more effectively altered cadence and double support time while verbal cues more consistently increased vastus lateralis and medial gastrocnemius activity. The effectiveness of these methods in fostering motor relearning in the longer term is an important area for future research. Implications for Rehabilitation Therapist cueing alters muscle activity on hemiparetic side with no effects on symmetry. Tactile cues, more so than verbal cues, increase cadence and reduce time in double support. Verbal cues are more effective at increasing vastus lateralis and plantarflexor muscle activity.

Unilateral Rolling of the Foot did not Affect Non-Local Range of Motion or Balance.

Non-local or crossover (contralateral and non-stretched muscles) increases in range-of-motion (ROM) and balance have been reported following rolling of quadriceps, hamstrings and plantar flexors. Since there is limited information regarding plantar sole (foot) rolling effects, the objectives of this study were to determine if unilateral foot rolling would affect ipsilateral and contralateral measures of ROM and balance in young healthy adults. A randomized within-subject design was used to examine non-local effects of unilateral foot rolling on ipsilateral and contralateral limb ankle dorsiflexion ROM and a modified sit-and-reach-test (SRT). Static balance was also tested during a 30 s single leg stance test. Twelve participants performed three bouts of 60 s unilateral plantar sole rolling using a roller on the dominant foot with 60 s rest intervals between sets. ROM and balance measures were assessed in separate sessions at pre-intervention, immediately and 10 minutes post-intervention. To evaluate repeated measures effects, two SRT pre-tests were implemented. Results demonstrated that the second pre-test SRT was 6.6% higher than the first pre-test (p = 0.009, d = 1.91). There were no statistically significant effects of foot rolling on any measures immediately or 10 min post-test. To conclude, unilateral foot rolling did not produce statistically significant increases in ipsilateral or contralateral dorsiflexion or SRT ROM nor did it affect postural sway. Our statistically non-significant findings might be attributed to a lower degree of roller-induced afferent stimulation due to the smaller volume of myofascia and muscle compared to prior studies. Furthermore, ROM results from studies utilizing a single pre-test without a sufficient warm-up should be viewed critically.

Population Differences in Postural Response Strategy Associated with Exposure to a Novel Continuous Perturbation Stimuli: Would Dancers Have Better Balance on a Boat?

Central or postural set theory suggests that the central nervous system uses short term, trial to trial adaptation associated with repeated exposure to a perturbation in order to improve postural responses and stability. It is not known if longer-term prior experiences requiring challenging balance control carryover as long-term adaptations that influence ability to react in response to novel stimuli. The purpose of this study was to determine if individuals who had long-term exposure to balance instability, such as those who train on specific skills that demand balance control, will have improved ability to adapt to complex continuous multidirectional perturbations. Healthy adults from three groups: 1) experienced maritime workers (n = 14), 2) novice individuals with no experience working in maritime environments (n = 12) and 3) individuals with training in dance (n = 13) participated in the study. All participants performed a stationary standing task while being exposed to five 6 degree of freedom motions designed to mimic the motions of a ship at sea. The balance reactions (change-in-support (CS) event occurrences and characteristics) were compared between groups. Results indicate dancers demonstrated significantly fewer CS events than novices during the first trial, but did not perform as well as those with offshore experience. Linear trend analyses revealed that short-term adaptation across all five trials was dependent on the nature of participant experience, with dancers achieving postural stability earlier than novices, but later than those with offshore experience. These results suggest that long term previous experiences also have a significant influence on the neural control of posture and balance in the development of compensatory responses.

Is gamma loop dysfunction related to bilateral inhibition in anterior knee pain?

INTRODUCTION: The potential relationship between bilateral quadriceps inhibition in individuals with unilateral anterior knee pain (AKP) and gamma loop dysfunction is examined in this study. METHODS: Twelve individuals with unilateral AKP and 10 healthy controls were recruited. Quadriceps voluntary activation (%VA) was quantified using a triggered interpolated twitch technique. Gamma loop function was assessed through knee extension maximum voluntary isometric contractions before and after 20 minutes of 50-Hz patellar tendon vibration. RESULTS: The AKP group exhibited 5.7% lower %VA bilaterally compared with controls (P = 0.039, Cohen d = 0.79). After prolonged vibration, both groups exhibited an average 8.5% reduction in knee extension force in each limb (P < 0.001, Cohen d = 0.85). CONCLUSIONS: Significant force reductions after vibration suggest that gamma loop dysfunction was not seen in either control or AKP participants. Bilateral quadriceps inhibition in the AKP group does not appear to be associated with gamma loop dysfunction.

Effect of unilateral knee extensor fatigue on force and balance of the contralateral limb.

PURPOSE: Fatigue in one limb can decrease force production in the homologous muscle as well as other muscles of the non-fatigued limb affecting balance. The objective of the study was to examine the effect of unilateral knee extensor fatigue on the non-fatigued limb's standing balance, muscle force and activation. METHOD: Sixteen healthy male subjects performed pre-fatigue balance trials, warm-up exercises, maximum voluntary isometric contractions, a knee extensors fatigue protocol, and post-fatigue balance trials. The fatigue protocol consisted of sets of 15 consecutive isometric contractions of 16 s each with 4 s recovery between repetitions, which were performed at 30% peak force for the dominant knee extensor muscles. Additional sets of contractions continued until a 50% decrease in MVIC knee extensor force was observed. Pre- and post-fatigue balance assessment consisted of transition from double to single leg standing and also single leg standing trials, which were performed bilaterally and in randomized order. RESULT: The peak force and F100 were significantly decreased by 44.8% (ES = 2.54) and 39.9% (ES = 0.59), respectively, for the fatigued limb post-fatigue. There were no significant changes in the non-fatigued limb's muscle force, activation, muscle onset timing or postural stability parameters. CONCLUSION: While the lack of change in non-fatigued limb force production is in agreement with some of the previous literature in this area, the lack of effect on postural measures directly contradicts earlier work. It is hypothesized that discrepancies in the duration and the intensity of the fatigue protocol may have accounted for this discrepancy.

Determining the activation of gluteus medius and the validity of the single leg stance test in chronic, nonspecific low back pain.

OBJECTIVES: To determine the activation of the gluteus medius in persons with chronic, nonspecific low back pain compared with that in control subjects, and to determine the association of the clinical rating of the single leg stance (SLS) with chronic low back pain (CLBP) and gluteus medius weakness. DESIGN: Cohort-control comparison. SETTING: Academic research laboratory. PARTICIPANTS: Convenience sample of people (n=21) with CLBP (>12wk) recruited by local physiotherapists, and age- and sex-matched controls (n=22). Subjects who received specific pain diagnoses were excluded. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Back pain using the visual analog scale (mm); back-related disability using the Oswestry Back Disability Index (%); strength of gluteus medius measured using a hand dynamometer (N/kg); SLS test; gluteus medius onset and activation using electromyography during unipedal stance on a forceplate. RESULTS: Individuals in the CLBP group exhibited significant weakness in the gluteus medius compared with controls (right, P=.04; left, P=.002). They also had more pain (CLBP: mean, 20.50mm; 95% confidence interval [CI], 13.11-27.9mm; control subjects: mean, 1.77mm; 95% CI, -.21 to 3.75mm) and back-related disability (CLBP: mean, 18.52%; 95% CI, 14.46%-22.59%; control subjects: mean, .68%; 95% CI, -.41% to 1.77%), and reported being less physically active. Weakness was accompanied by increased gluteus medius activation during unipedal stance (R=.50, P=.001) but by no difference in muscle onset times. Although greater gluteus medius weakness was associated with greater pain and disability, there was no difference in muscle strength between those scoring positive and negative on the SLS test (right: F=.002, P=.96; left: F=.1.75, P=.19). CONCLUSIONS: Individuals with CLBP had weaker gluteus medius muscles than control subjects without back pain. Even though there was no significant difference in onset time of the gluteus medius when moving to unipedal stance between the groups, the CLBP group had greater gluteus medius activation. A key finding was that a positive SLS test did not distinguish the CLBP group from the control group, nor was it a sign of gluteus medius weakness.

Effect of using a suspension training system on muscle activation during the performance of a front plank exercise.

The objective of the study was to examine the effect of suspension training on muscle activation during performance of variations of the plank exercise. Twenty-one participants took part. All individuals completed 2 repetitions each of 4 different plank exercises that consisted of a floor based plank, or planks with arms suspended, feet suspended, or feet and arms suspended using a TRX Suspension System. During plank performance, muscle activation was recorded from rectus abdominis, external oblique, rectus femoris, and serratus anterior (SA) muscles using electromyography. All planks were performed for a total of 3 seconds. Resulting muscle activation data were amplitude normalized, and root mean square activation was then determined over the full 3 second duration of the exercise. A significant main effect of plank type was found for all muscles. Post hoc analysis and effect size examination indicated that abdominal muscle activation was higher in all suspended conditions compared to the floor based plank. The highest level of abdominal muscle activation occurred in the arms suspended and arms/feet suspended conditions, which did not differ from one another. Rectus femoris activation was greatest during the arms suspended condition, whereas SA activity peaked during normal and feet suspended planks. These results indicate that suspension training as performed in this study seems to be an effective means of increasing muscle activation during the plank exercise. Contrary to expectations, the additional instability created by suspending both the arms and feet did not result in any additional abdominal muscle activation. These findings have implications in prescription and progression of core muscle training programs.

Does performing drop jumps with additional eccentric loading improve jump performance?

Previous investigators have speculated that applying additional external load throughout the eccentric phase of the jumping movement could amplify the stretch-shortening cycle mechanism and modulate jumping performance and jump exercise intensity. The aims of this study, therefore, were to determine the effect of increased eccentric phase loading, as delivered using an elastic device, on drop jumps (DJs) performed from different drop heights. Of specific interest were changes in (a) the kinetics; eccentric and concentric impulse, rate of force development (RFD), concentric velocity and (b) the electromyographic (EMG) activity of leg muscles. In a randomized repeated-measure study, 15 highly resistance trained male subjects performed DJs from 3 heights (20, 35, and 50 cm) under 3 different conditions: body weight only (free DJ) and with elastic bands providing downward force equivalent to 20% (+20% DJ) and 30% (+30% DJ) of body mass. All DJs were recorded using video and force plate data that were synchronized with EMG data. Results demonstrated that using additional tensile load during the airborne and eccentric phases of the DJ could enhance eccentric impulse (p = 0.042) and RFD (p < 0.001) and resulted in small to moderate effect size (ES) increases in quadriceps intergrated EMG across the eccentric phase (0.23 > ES > 0.51). The observed greater eccentric loading, however, did not immediately alter concentric kinetics and jump height nor did it alter muscle activation levels during this phase. The findings indicated that, in addition to the conventional technique of increasing drop height, using a tensile load during the airborne and eccentric phases of the DJ could further improve eccentric loading of DJs. As it has been suggested that eccentric impulse and RFD are indicators of DJ exercise intensity, these findings suggest that the loaded DJs, using additional elastic load, may be an effective technique for improving DJ exercise intensity without acute effects on the jumping performance and neuromuscular activation level in highly trained athletes.

Relative static stretch-induced impairments and dynamic stretch-induced enhancements are similar in young and middle-aged men.

Middle-aged individuals may not respond in a similar manner as younger individuals. The study's objective was to examine the effect of static (SS) and dynamic stretching (DS) in young and middle-aged men on subsequent performance. Ten young (22 ± 1.4 years) and 8 middle-aged men (46.3 ± 6.5 years) participated in 3 conditions consisting of SS (4 × 30 s for right and left quadriceps, hamstrings, and plantar flexors), DS (8 × 30 s of bilateral butt kicks, walking lunges, and plantar flexors) and control. Dependent variables included sit and reach, hip extension flexibility, countermovement jump (CMJ) height, drop jump (DJ) height, static balance, reaction (RT) and movement time (MT). Measurements were taken pre-intervention, post- and 10 min post-intervention. A 3-way repeated measurement ANOVA revealed that the younger men had higher jump heights, faster RT and MT, and greater flexibility than the middle-aged men. DS significantly enhanced DJ (p = 0.04) and CMJ (p = 0.006) height compared with SS and control conditions. SS (p < 0.0001) and DS (p = 0.004) post-intervention sit and reach scores were significantly greater than pre-intervention scores. There were no significant differences between the SS and DS sit and reach scores. CMJ heights were impaired (p = 0.04) by SS. Conversely, DS post-intervention jump heights were significantly (p < 0.0001) higher than SS post-, control post-, and control 10 min post-intervention. SS-induced impairments and DS-induced enhancements of CMJ height were not affected by age. DS provided similar improvements in sit and reach scores as SS. DS is recommended as the most appropriate stretching routine prior to work or athletic performance for younger and middle-aged men.

Swing phase kinetics and kinematics of knee replacement patients during obstacle avoidance.

Proper knee joint function is essential for safe and effective mobility within a complex environment. Following knee joint replacement, joint structure and function are altered, often requiring individuals to adjust normal movement patterns in order to adapt to these changes. Such adaptations may either improve function or lead to movement patterns that may potentially be unsafe for individuals. To investigate this issue, a group of individuals who had undergone knee replacement was examined while performing an obstacle avoidance task. Their performance was compared with that of healthy age-matched controls. Participants walked along a 10 m walkway a total 48 times. Trials were divided equally between unobstructed walking and clearing a 6 or 18 cm obstacle during both right and left limb lead. Lead limb kinetic and kinematic variables were examined and revealed that members of the surgical group exhibited decreased active surgical knee flexion and diminished surgical knee flexor work. In order to maintain toe clearance at control levels, patients were observed to increase hip hiking and hip flexor work, in addition to laterally displacing the surgical toe during swing over the obstacle. Despite allowing individuals to maintain adequate toe clearance, these compensatory strategies may lead to an increased instability and pose a threat to safety in this population. In addition, an increased demand placed on the hip joint of the surgical limb may be undesirable in this population. Research aimed at determining how to best maximize surgical knee function must continue if these potential negative sequela are to be minimized.

Bilateral lower limb strategies used during a step-up task in individuals who have undergone unilateral total knee arthroplasty.

OBJECTIVE: The purpose of this study was to determine how bilateral lower limb joint function is altered by the combined effects of osteoarthritis and its treatment by total knee arthroplasty. DESIGN: Lower limb joint work of age-matched healthy, control participants was compared to surgical and non-surgical limb work in individuals who had undergone total knee arthroplasty. BACKGROUND: Research investigating outcomes following total knee arthroplasty has focussed primarily on the surgical knee, identifying deficits in surgical knee function. The existence of additional lower limb deficits and adjustments made by unaffected joints to complement these deficits, has yet to be examined. METHODS: Joint moments, power and work were calculated using bilateral lower limb force and kinematic data collected during a step-up to heights of 11.25 and 20 cm. RESULTS: Fifty percent of patients were unable to step onto the 20 cm step. At both step heights, when the surgical limb led the step-up, surgical knee work was less than controls. When the non-surgical limb led, deficits in non-surgical lead knee work were observed. In both cases, lead hip work increased. CONCLUSIONS: Work done by both surgical and non-surgical knees in a step-up task was lower than that done by healthy controls. This deficit was balanced by increased lead hip extensor work. RELEVANCE: These findings highlight the importance of including exercises that optimize bilateral knee and hip function in rehabilitation programs used following knee replacement. Clinicians working with this population can use this information to assist in the design of evidenced based treatment programs.