Low back pain and biomechanical characteristics of back muscles in firefighters.

Firefighters often experience low back pain (LBP), but their back muscle characteristics are not well studied. This study aimed to 1) compare the biomechanical characteristics of back muscles and self-reported back disabilities in frontline firefighters with and without LBP history, and 2) examine the relationships between back disability and biomechanical measurements. We recruited 42 male firefighters and assessed their perceived pain and disabilities, maximum isometric back extension strength, passive stiffness, and fatigability of the longissimus. 54.8% of the participants experienced LBP within the past year. Those indicating higher pain intensity also had greater disability as indicated by the Oswestry Disability Index. There were no significant differences in strength, stiffness or fatigability of the back muscles between firefighters with and without LBP history. Multiple linear regression analysis revealed no significant relationship between the back disability and any biomechanical or demographic measures, likely due to the high functional abilities of the participants.

Approximately 50% of the firefighters who participated in the study experienced low back pain in the past 12 months. Since the pain level was mild to moderate, most of them continued to report to work. Biomechanically, there were no differences in back muscle strength, stiffness, resistance to fatigue, or left-right symmetry between firefighters with and without back pain history. Back disabilities were not related to any biomechanical measures or demographics including age and body mass index. Overall, despite experiencing some back pain, these frontline firefighters are highly functional and did not show diminished physical or neuromuscular responses.

Effects of foot orthosis on ground reaction forces and perception during short sprints in flat-footed athletes.

Prefabricated foot orthosis (FO) is commonly worn for flat foot management. This study aimed to investigate the kinetic and perceptual effects of wearing prefabricated FO among flat-footed athletes during bouts of sprints. Twenty male sprint-based sports athletes who had flat foot bilaterally ran at three test speeds (5, 6, 7 m/s) under two conditions: prefabricated FO and sham FO. Ground reaction force (GRF) variables and subjective perceptions were recorded. Kinetic variability of GRF variables were computed to indicate step-to-step variance. Biomechanically, wearing prefabricated FOs increased vertical impact force (p =.005), loading rate (p =.001), and kinetic variability of peak propulsive force (p =.038) and loading rate (p =.019) during sprinting speeds across 5 to 7 m/s. Subjectively, prefabricated FO provided better arch support (p =.001) but resulted in reduced forefoot cushioning (p =.001), heel cushioning (p =.002), and overall comfort (p =.008).

Between-limb asymmetry in kinetic and temporal characteristics during bilateral plyometric drop jumps from different heights.

This study investigated the between-limb asymmetry in kinetic and temporal characteristics during bilateral plyometric drop jumps from different heights. Seventeen male basketball players performed drop jumps from 3 heights on two platforms in randomized orders. Vertical ground reaction force data were analysed with respect to the lead limb (i.e. the limb stepping off the raised platform first) and trail limb. Peak forces and loading rates of each limb were calculated. The absolute time differential between the two limbs at initial ground contact and takeoff were determined. The frequency of symmetrical landing and taking off with "both limbs together" were counted using 3 time windows. Results showed that the lead limb displayed higher peak forces and loading rates than the trail limb across all heights (p <.05). As drop height increased, the absolute time differentials decreased at initial ground contact (p <.001) but increased at takeoff (p =.035). The greater the preset time window, the more landings and takeoffs were classified as bilaterally symmetrical. In conclusion, higher drop heights allowed subjects to become more bilaterally symmetrical in the timing of landing but this reduction in temporal asymmetry did not accompany with any reduction in kinetic asymmetry.

Effect of caffeine ingestion on free-throw performance in college basketball players.

BACKGROUND: It is currently unclear whether pre-exercise caffeine ingestion can improve free-throw shooting performance, a vital skill in basketball. The purpose of this study was to investigate the effects of caffeine on free-throw shooting performance in college-aged basketball players. METHODS: Twelve males (23.1 ± 1.9 years; 180.1 ± 8.8 cm; 77.1 ± 12.4 kg) and six females (22.0 ± 1.3 years; 169.4 ± 8.9 cm; 67.0 ± 11.1 kg) who competed at the college level ingested 6 mg per kg of body mass of (a) caffeine or (b) maltodextrin (placebo) on two separate occasions in a random order. After 60 min, they performed five sets of a match-simulated basketball protocol comprising six sideline-to-sideline sprints on a standard basketball court followed by two free-throws after each set. The number of successful shots was counted. Heart rate and rating of perceived exertion (RPE) after each sprint set were also recorded. RESULTS: Caffeine ingestion did not improve overall free-throw success (caffeine = 6.1 ± 1.7 vs. placebo = 5.5 ± 2.0; p = 0.34) compared with placebo across all five sets. There was no change in shooting accuracy across sprint sets in either trial despite significant increases in both heart rate and RPE. Caffeine increased heart rate (p = 0.02) but had no effect on RPE (p = 0.57) across five sets compared with placebo. CONCLUSIONS: Ingestion of 6 mg of caffeine per kg of body mass did not improve basketball free-throw performance. Free-throw performance did not deteriorate with increasing number of sprint sets.

Effect of Post-Exercise Massage on Passive Muscle Stiffness Measured Using Myotonometry - A Double-Blind Study.

It is commonly believed that massage can reduce muscle stiffness and is desirable for recovery from exercise. However, the effect massage on muscle stiffness following eccentric exercises is currently unknown. This study aimed to examine the effect of post-exercise massage on passive muscle stiffness over a five-day period. A randomised cross-over study design was adopted. After 40 minutes of downhill running, 18 male recreational runners had one leg received a 16-minute massage and the contralateral leg received a 16-minute sham ultrasound treatment. Passive stiffness for four leg muscles (rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius) was assessed using myotonometry at baseline, immediately post-run, post-treatment, 24, 48, 72, and 96 hours post-run. A 2 (treatment) × 7 (time) mixed ANOVA was conducted with a robust procedure on the myotonometry data of each leg muscle to examine the effect of treatment on stiffness. Passive stiffness for all muscles changed over time but no treatment effect was found. Stiffness increased at 24 hours post-run and remained elevated from baseline levels for up to 96 hours across all four muscles. Significant treatment × time interaction was only found in the tibialis anterior but no post-hoc differences were identified. Passive stiffness of major leg muscles increased after a bout of unaccustomed eccentric exercise and remained elevated for up to four days post-exercise. Compared with the placebo treatment, post-exercise massage had no beneficial effect in alleviating altered muscle stiffness in major leg muscles.

Effect of body mass and midsole hardness on kinetic and perceptual variables during basketball landing manoeuvres.

This study investigated the effects of body mass and shoe midsole hardness on kinetic and perceptual variables during the performance of three basketball movements: (1) the first and landing steps of layup, (2) shot-blocking landing and (3) drop landing. Thirty male basketball players, assigned into "heavy" (n = 15, mass 82.7 ± 4.3 kg) or "light" (n = 15, mass 63.1 ± 2.8 kg) groups, performed five trials of each movement in three identical shoes of varying midsole hardness (soft, medium, hard). Vertical ground reaction force (VGRF) during landing was sampled using multiple wooden-top force plates. Perceptual responses on five variables (forefoot cushioning, rearfoot cushioning, forefoot stability, rearfoot stability and overall comfort) were rated after each movement condition using a 150-mm Visual Analogue Scale (VAS). A mixed factorial analysis of variance (ANOVA) (Body Mass × Shoe) was applied to all kinetic and perceptual variables. During the first step of the layup, the loading rate associated with rearfoot contact was 40.7% higher in the "heavy" than "light" groups (P = .014) and 12.4% higher in hard compared with soft shoes (P = .011). Forefoot peak VGRF in a soft shoe was higher (P = .011) than in a hard shoe during shot-block landing. Both "heavy" and "light" groups preferred softer to harder shoes. Overall, body mass had little effect on kinetic or perceptual variables.

Subjective evaluation of running footwear depends on country and assessment method: a bi-national study.

This study examined (1) the perception of running shoes between China (Beijing) and Singapore and (2) whether running shoe preference depended on assessment methods. One hundred (n = 50 each country) Chinese males subjectively evaluated four shoe models during running by using two assessment procedures. Procedure 1 used a visual analogue scale (VAS) to assess five perception variables. Procedure 2 was a 'head-to-head' comparison of two shoes simultaneously (e.g. left foot: A and right foot: B) to decide which model was preferred. VAS scores were consistently higher in Beijing participants (p < .001), indicating a higher degree of liking. Singapore participants used the lower end but a wider range of the 15 cm scale for shoe discrimination. Moderate agreement was seen between the VAS and 'head-to-head' procedures, with only 14 out of 100 participants matched all 6 pairwise comparisons (median = 4 matches). Footwear companies and researchers should be aware that subjective shoe preference may vary with assessment methods. Practitioner Summary: Footwear preference depends on country and assessment methods. Running shoe perception differed between Beijing and Singapore Chinese, suggesting that footwear recommendation should be country-specific. Individuals' shoe preference measured by visual analogue scale when wearing complete pairs may not reflect that when directly comparing different models in left and right feet.

Start-up time and walking speed in older adults under loaded conditions during simulated road crossing.

UNLABELLED: BACKGROUND/STUDY CONTEXT: The safety of older pedestrians in road crossing has received considerable attention but previous studies measure gait characteristics only under unloaded conditions. The aim of this study was to investigate the start-up time and walking speed under loaded conditions that reflect daily activities of older adults in Singapore. METHODS: Thirty-two older adults (age (SD) = 69.4 (7.0) years) and 20 young controls (age (SD) = 23.1 (2.0) years) walked under four conditions: (1) unloaded, (2) pushing a stroller loaded with 10 kg, (3) pulling a shopping cart loaded with 15 kg, and (4) carrying two shopping bags each loaded with 2 kg. Start-up time was determined from video recordings and walking speed measured using timing gates. A mixed-model analysis of variance (ANOVA; age by walking condition) with repeated measures was applied. RESULTS: Start-up times were slower in the stroller and shopping cart conditions compared with the unloaded and shopping bags conditions. Loading reduced walking speed, with the shopping cart being the slowest, followed by the stroller and then the shopping bags. A significant interaction was found, with young controls reducing their speeds more substantially while handling the stroller/cart than older participants. CONCLUSION: Loading caused a compromise in start-up time and walking speed. The start-up time was slower when pushing a stroller or pulling a shopping cart but remained unaffected by carrying shopping bags. Speed was reduced under all loaded conditions, with a greater effect in young than older participants when handling a stroller or shopping cart.

Hamstrings Hypertrophy is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training.

INTRODUCTION: The hamstring muscles play a crucial role in sprint running, but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) or lengthened state eccentric training (LSET, isoinertial weight-stack resistance in an accentuated hip-flexed position), to habitual activity (no training controls: CON). METHODS: 42 healthy young males completed 34 sessions of NHT or LSET over 12 weeks or served as CON (n = 14/group). MRI-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric and isometric contractions were assessed pre- and post-training. RESULTS: LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) in-between. CONCLUSIONS: These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT.

Effects of isometric and dynamic postactivation potentiation protocols on maximal sprint performance.

This study examined the effects of 3 types of postactivation potentiation (PAP) protocols (single-joint isometric, multijoint isometric, and multijoint dynamic) on subsequent 10-m, 20-m and 30-m sprint performance in 12 well-trained male track athletes (mean ± SD age = 22.4 ± 3.2 years). The subjects performed 4 protocols in a randomized order on different days as follows: control (4 minutes of passive rest), maximum voluntary isometric knee extension (3 repetitions of 3-second isometric knee extension), maximum voluntary isometric back squat (3 repetitions of 3-second isometric squat), and dynamic back squat (3 repetitions of back squats at 90% 1 repetition maximum). After each protocol, a 4-minute recovery period was incorporated before a 30-m maximal sprint assessment. Maximal sprint times at 10 m, 20 m, and 30 m were measured using timing gates to reflect sprint performance. One-way repeated measures analyses of variance revealed no differences in sprint performance among the 4 protocols at 10-m, 20-m, or 30-m intervals. There were, however, large individual variations in the response to the PAP protocols with some athletes benefiting from the PAP effect and others not. In summary, this study showed no enhancement of short-distance sprint performance after PAP protocols with a 4-minute recovery period, regardless of isometric or dynamics, single-joint or multijoint. Coaches considering the use of PAP protocols to improve sprinting performance of their athletes should exploit the effectiveness of different PAP protocols on an individual basis.

Differences in the mechanics of takeoff in reverse and forward springboard somersaulting dives.

Forward and reverse springboard somersaulting dives use similar approaches with a hurdle step prior to the final board contact phase during which forward rotation is produced in forward takeoffs and backward rotation in reverse takeoffs. This study compared forward and reverse takeoffs for joint strength, activation complexity, technique kinematics, and rotation potential. A planar 8-segment torque-driven computer simulation model of springboard diving takeoff was used to determine isometric joint strength by matching performances of a forward 2½ somersault dive and a reverse 1½ somersault dive. Activation complexity for the reverse takeoff was increased to achieve a similar closeness of match as for the forward takeoff. Takeoff technique was optimised to maximise rotation potential of forward and reverse somersaulting dives. Kinematics at touchdown, lowest point and takeoff were compared for the optimised forward and reverse takeoff simulations. It was found that the optimised reverse somersaulting dive exhibited greater isometric strength for ankle plantarflexion and shoulder flexion, greater joint torque activation complexity for ankle plantarflexion and for knee flexion. There was also less forward motion during board depression, more hip extension and knee flexion during the later stages of board recoil, less capacity for rotation potential, and greater vertical velocity at takeoff.

Immediate comfort perception of 3D-printed foot orthoses in individuals with unilateral heel pain.

BACKGROUND: Custom-made foot orthoses (FOs) play an integral part in managing foot disorders. Traditional FO fabrication is time-consuming and labor intensive. Three-dimensional (3D) printed FOs save time and cost compared with the traditional manufacturing process. To date, the differences in dimensions and comfort perception of these orthoses have not been compared in a pathological population. OBJECTIVE: Compare the dimensions between 3D-printed and traditionally made FOs and comfort perception between 3D-printed, traditionally made, and no FOs in individuals with flatfeet and unilateral heel pain. STUDY DESIGN: Within-subject single-blinded randomized crossover study design. METHODS: Thirteen participants had custom-made FOs using 3D-printing and traditional processes. Orthotic lengths, widths, arch heights, and heel cup heights were compared. Participants performed walking trials under three conditions: (1) no orthoses, (2) 3D-printed orthoses, and (3) traditionally made orthoses. Comfort perception was recorded. Orthotic dimensions were compared using paired t tests, and comfort perception were compared using one-way multiple analysis of variance and Bonferroni post hoc tests. RESULTS: Three-dimensional-printed orthoses were wider, have higher arch heights, and heel cup heights compared with traditionally made FOs (medium to large effect sizes). There was a difference in comfort perception between the three orthotic conditions, F(12,62) = 1.99, P = 0.04; Wilk Λ = 0.521, ηp2= 0.279. Post hoc tests show that there is no difference in comfort perception between the 3D-printed and traditionally made FOs. Both FOs were significantly more comfortable than no orthoses. CONCLUSIONS: Three-dimensional printing seems to be a viable alternative orthotic fabrication option. Future studies should compare the biomechanical effects of 3D-printed and traditionally made FOs.

The biomechanical effects of 3D printed and traditionally made foot orthoses in individuals with unilateral plantar fasciopathy and flat feet.

BACKGROUND: Foot orthoses (FOs) are used to manage foot pathologies such as plantar fasciopathy. 3D printed custom-made FOs are increasingly being manufactured. Although these 3D-printed FOs look like traditionally heat-moulded FOs, there are few studies comparing FOs made using these two different manufacturing processes. RESEARCH QUESTION: How effective are 3D-printed FOs (3D-Print) compared to traditionally-made (Traditional) or no FOs (Control), in changing biomechanical parameters of flat-footed individuals with unilateral plantar fasciopathy? METHODS: Thirteen participants with unilateral plantar fasciopathy walked with shoes under three conditions: Control, 3D-print, and Traditional. 2 × 3 repeated measures analysis of variance (ANOVAs) with Bonferroni post-hoc tests were used to compare discrete kinematic and kinetic variables between limbs and conditions. Waveform analyses were also conducted using statistical parametric mapping (SPM). RESULTS: There was a significant condition main effect for arch height drop (p = 0.01; ηp2 =0.54). There was 0.87 mm (95% CI [-1.84, -0.20]) less arch height drop in 3D-print compared to Traditional. The SPM analyses revealed condition main effects on ankle moment (p < 0.001) and ankle power (p < 0.001). There were significant differences between control condition and both 3D-print and Traditional conditions. For ankle moment and power, there were no differences between 3D-print and Traditional conditions. SIGNIFICANCE: 3D-printed FOs are more effective in reducing arch height drop, whist both FOs lowered ankle plantarflexion moment and power compared to no FOs. The results support the use of 3D-printed FOs as being equally effective as traditionally-made FOs in changing lower limb biomechanics for a population of flat-footed individuals with unilateral plantar fasciopathy.

Effect of shoe modifications on biomechanical changes in basketball: A systematic review.

Shoe modifications are suggested to reduce the risks of injuries and improve sports performance in basketball. This review aimed to critically evaluate the effect of different basketball shoe modifications on biomechanical changes in basketball movements. Searches of four major databases for biomechanics studies which evaluated footwear construction/material in basketball yielded 442 records. After duplicates were removed and exclusion/inclusion criteria applied to the titles and abstracts, 20 articles remained for further quality assessment. Two reviewers independently confirmed 17 articles (n = 340 participants), with 95.5% of agreement between judgements, which were included for review. The results were categorised based on the following shoe modifications: (a) cushioning, (b) midsole hardness, (c) collar height, (d) outsole traction component, (e) forefoot bending stiffness and (f) shoe mass that influence lower limb biomechanics. The included articles revealed that 1) better shoe cushioning or softer midsole is related to better impact attenuation in passive/unanticipated situations, 2) high shoe collars are effective to improve ankle stability in jumping and cutting tasks, 3) increased shoe traction and forefoot bending stiffness can improve basketball jump, sprint and/or cut performances and 4) lighter shoe mass results in better jump and/or cut performances when the shoe mass is known.

Air pistol shooting: upper limb muscle activation between training and simulated competition.

Heightened stress during air pistol competitions may impair shooters' abilities to maintain gun stability, resulting in inferior performance. This study aimed to compare the pre-trigger muscle activation levels of upper muscles in 10-m air pistol shooters between training and simulated competition conditions. Seven sub-elite shooters from the Singapore National Youth Air Pistol Team shot 30 shots in a training versus simulated competition condition in randomised orders on separate days. Muscle activation for the forearm and shoulder muscles, namely extensor carpi radialis, flexor carpi ulnaris, anterior deltoid, and posterior deltoid, were recorded using electromyography (EMG). Shooting performance was evaluated by total shot scores. Stress level was monitored via heart rate and the Mental Readiness Form-3. No statistically significant differences were found in EMG, performance, or stress-related variables between conditions, although moderate-to-large effect sizes were observed in some muscle activation and self-reported stress indicators. Analysis of individual performances using smallest worthwhile change showed that two participants improved under the simulated competition condition, while two declined, and three remained unaffected. In conclusion, sub-elite youth air pistol shooters were able to exhibit good neuromuscular control under high anxiety situations and thus their performance was largely unaffected.

Hip extension during the come-out of multiple forward and inward pike somersaulting dives is controlled by eccentric contraction of the hip flexors.

A modelling approach was used in the present study to investigate the role of the hip muscles during the come-out of forward and inward multiple somersaulting dives in a pike position. A planar two-segment model was used to simulate the somersault and come-out of three commonly performed dives from a 3-m springboard: forward two-and-one-half somersault pike dive (105B), forward three-and-one-half somersault pike dive (107B), and inward two-and-one-half somersault pike dive (405B). Three simulations were run for each dive: (1) hip angle was constrained to be constant, (2) hip torque was removed after 0.1 s, and (3) hip angle was constrained to a typical come-out time history used by elite divers. Simulation results indicated that hip flexion torque was required both to maintain a rigid pike position during somersault (range = 205.5-282.3 Nm) and to control the hip extension movement during the come-out (peak torque range = 355.8-548.1 Nm) in forward and inward multiple somersaulting dives. Coaches and divers should be aware that dry-land exercise drills producing hip extension movement by concentric actions of the hip extensor muscles do not replicate the neuromuscular control during the come-out of fast rotating dives.

Test-retest reliability of a clinical foot assessment device for measuring first metatarsophalangeal joint quasi-stiffness.

BACKGROUND: The stiffness of the first metatarsophalangeal joint (MTPJ) is of interest in cases such as hallux rigidus and apropulsive gait. Subjective rating of joint mobility as 'hypermobile, normal, or stiff' is an unreliable method. Previous instruments for the assessment of first MTPJ stiffness can be too hard and uncomfortable for test subjects. Recently, a new device using a load cell and optical fiber with fiber Bragg grating (FBG) sensors was developed to provide a comfortable means of clinical foot assessment. This study aimed to evaluate the test-retest reliability of this FBG-load cell device in measuring the first MTPJ quasi-stiffness. METHODS: The left foot of 13 female subjects were measured twice for their first MTPJ quasi-stiffness, approximately seven days apart. The FBG-load cell device measured the MTPJ range of motion from a resting position to maximum dorsiflexion and then returning to the resting start-position. The force applied by a clinician to displace the toe was simultaneously recorded using the load cell. The quasi-stiffness over the "working range" in loading and unloading directions were determined from the slope of the torque-angular displacement graph. The test-retest reliability of the MTPJ quasi-stiffness was evaluated using intra-class correlation coefficient [ICC (2,1)]. RESULTS: The reliability was almost perfect for MTPJ quasi-stiffness over the loading phase (ICC = 0.814), moderate for MTPJ quasi-stiffness over the unloading phase (ICC = 0.477) and moderate for MTPJ maximum range (ICC = 0.486). CONCLUSION: The foot assessment device comprising FBG and load cell was able to reliably measure the first MTPJ quasi-stiffness in a clinical setting. The measurement reliability was higher during the loading phase than the unloading phase.

Wearing the F-Scan mobile in-shoe pressure measurement system alters gait characteristics during running.

This study investigated the influence of wearing an F-Scan mobile in-shoe pressure measurement system on running characteristics. Six subjects ran on a treadmill at three speeds (3.5 ms(-1), 4.5 ms(-1) and 5.4 ms(-1)) with and without wearing the F-Scan system while kinematic data were collected at 240 Hz using a motion capture system. Six gait cycles were selected for analysis, with touchdown and toe-off visually identified based on foot markers displacement. Spatio-temporal gait parameters including stride frequency, stride length, stride length relative to height, and stance time were determined. A 2x3 ANOVA with repeated measures (alpha=0.05) was performed to identify differences in each gait parameter between running with and without the F-Scan system at different speeds. Wearing the F-Scan system did not affect the stance time but lead to an increase in stride frequency (P<0.05) and a decrease in stride length (P<0.05) and relative stride length (P<0.05). As speed increased, stance time decreased while stride frequency, stride length and relative stride length increased (all P<0.001). These results imply that wearing the F-Scan system alters gait characteristics and therefore data obtained may not represent those in a real life setting, at least in the case of running. One should take into account the potential risk of the movement of interest being altered when interpreting data obtained while subjects were wearing the F-Scan system. Future instrumentation should minimize the potential influence a measurement device may have on natural movement.

Perception of self-selected running speed is influenced by the treadmill but not footwear.

In this study, we examined whether self-selected overground running speed was consistent (1) with perceived overground speed on the treadmill and (2) among barefoot and three footwear conditions. Participants ran across a 20-m runway 10 times for each overground condition, with running speed calculated from kinematic data. For the treadmill condition, the participants were instructed to run at a speed that felt similar to their overground speed. This treadmill speed was chosen upon perception, with the display covered from the participant's view. Repeated-measures analysis of variance was used to detect differences in speed between overground and treadmill running, and also among barefoot and footwear conditions. Coefficient alpha (alpha) was calculated to determine repeatability of observations in each overground condition. The speed was higher during overground (3.65 +/- 0.40 m/s) than treadmill (2.25 +/- 0.75 m/s) running but did not differ among the barefoot and the three footwear conditions. Overall, overground speed was highly repeatable within an individual (alpha = 0.96-0.98). Researchers might consider using self-selected speed when investigating overground running mechanics with different foot-ground interface conditions. The influence of treadmill on the perception of speed may be related to shear force, running duration, joint load control, and/or other psychological factors.

Maximising forward somersault rotation in springboard diving.

Performance in the flight phase of springboard diving is limited by the amounts of linear and angular momentum generated during the takeoff phase. A planar 8-segment torque-driven simulation model combined with a springboard model was used to investigate optimum takeoff technique for maximising rotation in forward dives from the one metre springboard. Optimisations were run by varying the torque activation parameters to maximise forward rotation potential (angular momentum × flight time) while allowing for movement constraints, anatomical constraints, and execution variability. With a constraint to ensure realistic board clearance and anatomical constraints to prevent joint hyperextension, the optimised simulation produced 24% more rotation potential than a simulation matching a 2½ somersault piked dive. When 2 ms perturbations to the torque onset timings were included for the ankle, knee and hip torques within the optimisation process, the model was only able to produce 87% of the rotation potential achieved in the matching simulation. This implies that a pre-planned technique cannot produce a sufficiently good takeoff and that adjustments must be made during takeoff. When the initial onset timings of the torque generators were unperturbed and 10 ms perturbations were introduced into the torque onset timings in the board recoil phase, the optimisation produced 8% more rotation potential than the matching simulation. The optimised simulation had more hip flexion and less shoulder extension at takeoff than the matching simulation. This study illustrates the difficulty of including movement variability within performance optimisation when the movement duration is sufficiently long to allow feedback corrections.