Factors that influence field hockey footwear selection: An online survey.

BACKGROUND: Little is known about factors that influence footwear selection by field hockey players. METHODS: An online survey was used to collect data on participant demographics and physical characteristics, factors influencing footwear selection, perceptions regarding footwear design features on injury and performance, and experiences regarding usability. Nominal and ordinal data were described as absolute frequencies and relative frequencies. Free text responses were analysed using content analysis. Sex-related differences in quantitative and qualitative data were explored. RESULTS: A total of 401 hockey players completed the survey. Participants reported that fit, comfort, support, and cushioning were the most important factors when selecting hockey footwear. Most hockey players believed that stud design could influence athletic performance (65%) and injury risk (63%) but reported having no preference on outsole design or stud shape. Most participants (63%) used hockey-specific footwear, but 46% of female hockey players did not, with 40% using trail running footwear instead. Qualitative analysis revealed that hockey players, particularly female participants, encounter difficulties finding properly fitting footwear. They desire more options for wide or narrow feet and face challenges in accessing suitable hockey shoes due to limited choices and availability. CONCLUSIONS: With over a third of field hockey players not using hockey-specific footwear, future research should attempt to understand the reasons and assess the impact of different footwear features on comfort, performance, injury risk, and usability.

The use of wearable technology as an assessment tool to identify between-limb differences during functional tasks following ACL reconstruction. A scoping review.

OBJECTIVE: To report how wearable sensors have been used to identify between-limb deficits during functional tasks following ACL reconstruction and critically examine the methods used. METHODS: We performed a scoping review of studies including participants with ACL reconstruction as the primary surgical procedure, who were assessed using wearable sensors during functional movement tasks (e.g., balance, walking or running, jumping and landing) at all postsurgical time frames. RESULTS: Eleven studies met the inclusion criteria. The majority examined jumping-landing tasks and reported kinematic and kinetic differences between limbs (involved vs. unninvolved) and groups (injured vs. controls). Excellent reliability and moderate-strong agreement with laboratory protocols was indicated, with IMU sensors providing an accurate estimation of kinetics, but the number of studies and range of tasks used were limited. Methodological differences were present including, sensor placement, sampling rate, time post-surgery and type of assessment which appear to affect the outcome. CONCLUSIONS: Wearable sensors consistently identified between-limb and group deficits following ACL reconstruction. Preliminary evidence suggests these technologies could be used to monitor knee function during rehabilitation, but further research is needed including, validation against criterion measures. Practitioners should also consider how the methods used can affect the accuracy of the outcome.

Commonly used clinical criteria following ACL reconstruction including time from surgery and isokinetic limb symmetry thresholds are not associated with between-limb loading deficits during running.

OBJECTIVES: We included objective measures of gait and functional assessments to examine their associations in athletes who had recently commenced running after ACL reconstruction. DESIGN: Cross-sectional. SETTING: Sports medicine. PARTICIPANTS: 65 male athletes with a history of ACL reconstruction. MAIN OUTCOME MEASURES: Time from surgery, isokinetic knee extension/flexion strength (60°/s), and peak vertical ground reaction force (pVGRF) measured during running using an instrumented treadmill. We also investigated if a range of recommended isokinetic thresholds (e.g. > 70% quadriceps limb symmetry index) affected the magnitude of pVGRF asymmetry during running. RESULTS: There were significant relationships between quadriceps (r = 0.50) and hamstrings (r = 0.46) peak torque and pVGRF. Quadriceps peak torque explained a quarter of the variance in pVGRF (R2 = 0.24; p < 0.001). There was no association was between running pVGRF and time from surgery. Between-group differences in running pVGRF LSI% were trivial (d < 0.20) for all quadriceps and hamstring peak torque LSI thresholds. CONCLUSIONS: Current clinical criteria including time from surgery and isokinetic strength limb symmetry thresholds were not associated with lower pVGRF asymmetry measured during running. Quadriceps strength is important, but 'minimum symmetry thresholds' should be used with caution.

Lower medial hamstring activity after ACL reconstruction during running: a cross-sectional study.

OBJECTIVE: Anterior cruciate ligament reconstruction (ACLR) predisposes footballers for subsequent ACL and hamstring (HS) injury. This case series examines HS muscle activation patterns during the running in ACLR patients (bone-patellar tendon-bone (BTB) and (HS) graft) after completion of functional criteria allowing return to training. METHODS: Electromyography (EMG) recorded from medial and lateral HS bilaterally during treadmill running (12, 14 and 16 km/hour) from 21 male ACLR patients on average 7 months from surgery (5-9) that underwent (HS) (n=12) or BTB reconstruction (n=9) were compared with 19 healthy runners. Main outcome measures: EMG signal was normalised to peak during the running. Pairwise comparisons were made for each muscle group examining stance and swing activation for mean and peak EMG for each patient group and leg. RESULTS: Significantly lower relative peak activation in stance (not swing) phase for medial HS was seen for all conditions with effect sizes ranging from -0.63 (controls, BTB non-injured leg) to -1.09 (HS injured). For lateral HS only BTB injured were significantly lower in stance phase (-1.05). CONCLUSION: ACLR patients show neuromuscular alterations during different phases of running. The finding of reduced medial HS activity in stance phase might have implications for knee instability and HS muscle injury on resumption of sport.

Effect of speed and gradient on plantar force when running on an AlterG® treadmill.

BACKGROUND: Anti-gravity treadmills are used to decrease musculoskeletal loading during treadmill running often in return to play rehabilitation programs. The effect different gradients (uphill/downhill running) have on kinetics and spatiotemporal parameters when using an AlterG® treadmill is unclear with previous research focused on level running only. METHODS: Ten well-trained healthy male running athletes ran on the AlterG® treadmill at varying combinations of bodyweight support (60, 80, and 100% BW), speed (12 km/hr., 15 km/hr., 18 km/hr., 21 km/hr., and 24 km/hr), and gradients (- 15% decline, - 10, - 5, 0, + 5, + 10 + 15% incline), representing a total of 78 conditions performed in random order. Maximum plantar force and contact time were recorded using a wireless in-shoe force sensor insole system. RESULTS: Regression analysis showed a linear relationship for maximum plantar force with bodyweight support and running speeds for level running (p < 0.0001, adj. R2 = 0.604). The linear relationship, however, does not hold for negative gradients at speeds 12 & 15 km/h, with a relative 'dip' in maximum plantar force across all assisted bodyweight settings. CONCLUSIONS: Maximum plantar force peaks are larger with faster running and smaller with more AlterG® assisted bodyweight support (athlete unweighing). Gradient made little difference except for a downhill grade of - 5% decreasing force peaks as compared to level or uphill running.

Lower limb EMG activation during reduced gravity running on an incline. Speed matters more than hills irrespective of indicated bodyweight.

BACKGROUND: Progressive loading of the lower limb muscles during running on a positive pressure or reduced gravity (Alter-G™) treadmill is suggested as a rehabilitation strategy after muscle and tendon injury but the influence of running up or downhill and at higher speeds is not known, nor are the interaction effects of speed, inclination, and indicated bodyweight. RESEARCH QUESTION: What are the lower limb EMG activation levels and cadence when running up and downhill in normal and reduced gravity? METHODS: 10 recreationally active male athletes ran on a positive-pressure Alter-G™ treadmill at: 3 indicated bodyweights (60 %, 80 %, and 100 %); 5 speeds (12, 15, 18, 21, and 24 km/h); for incline, decline, and flat conditions (-15 %, -10 %, -5%, 0%, 5%, 10 %, and 15 %); while monitoring the surface EMG of 11 leg muscles as well as cadence (strides per minute). RESULTS AND SIGNIFICANCE: Linear mixed models showed significant effect of running speed, inclination, and indicated bodyweight, with interaction effects observed. Increasing running speed was associated with the largest change in activity, with smaller effects for increasing bodyweight and inclination. Downhill running was associated with reduced activity in all muscle groups, and more tightly clustered activity patterns independent of speed. Substantial variation in sEMG activity occurred in the flat and uphill conditions. Subject responses were quite variable for sEMG, less so for cadence. For the conditions examined, increasing running speed induced the largest changes in EMG of all muscles examined with smaller changes seen for manipulations of inclination and bodyweight.

Correction: Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football.

[This corrects the article DOI: 10.1371/journal.pone.0216364.].

Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football.

INTRODUCTION: An optimal range of shoe-surface traction (grip) exists to improve performance and minimise injury risk. Little information exists regarding the magnitude of traction forces at shoe-surface interface across a full season of elite football (soccer) using common football shoes. OBJECTIVE: To assess variation in shoe-surface traction of six different football shoe models throughout a full playing season in Qatar encompassing climatic and grass species variations. METHODS: Football shoes were loaded onto a portable shoe-surface traction testing machine at five individual testing time points to collect traction data (rotational and translational) on a soccer playing surface across one season. Surface mechanical properties (surface hardness, soil moisture) and climate data (temperature and humidity) were collected at each testing time point. RESULTS: Peak rotational traction was significantly different across shoe models (F = 218, df = 5, p <0.0001), shoe outsole groups (F = 316.2, df = 2, p < .0001), and grass species (F = 202.8, df = 4, p < 0.0001). No main effect for shoe model was found for translational traction (F = 2.392, p = 0.07). CONCLUSIONS: The rotational (but not translational) traction varied substantially across different shoe types, outsole groups, and grass species. Highest rotational traction values were seen with soft ground outsole (screw-in metal studs) shoes tested on warm season grass. This objective data allows more informed footwear choices for football played in warm/hot climates on sand-based elite football playing surfaces. Further research is required to confirm if these findings extend across other football shoe brands.

Reliability and validity of the Zebris FDM-THQ instrumented treadmill during running trials.

Little is known about the reliability, validity and smallest detectable differences of selected kinetic and temporal variables recorded by the Zebris FDM-THQ instrumented treadmill especially during running. Twenty male participants (age = 31.9 years (±5.6), height = 1.81 m (±0.08), mass = 80.2 kg (±9.5), body mass index = 24.53 kg/m2 (±2.53)) walked (5 km/h) and ran (10 and 15 km/h) on an instrumented treadmill, wearing running shoes fitted with Pedar-X insoles. A test-double retest protocol was conducted over two consecutive days. Maximal vertical force (Fmax), contact time (CT) and flight time (FT) data from 10 consecutive steps were collected. Within- and between-day reliability, smallest detectable differences (SDD) and validity (95% limits of agreement (LOA)) were calculated. ICC values for the Zebris for Fmax were acceptable (ICC ≥ 0.7) while CT and FT reliability indices were predominantly good (ICC ≥ 0.8) to excellent (ICC ≥ 0.9). The Zebris significantly underestimated Fmax when compared with the Pedar-X. The 95% LOA increased with speed. SDD ranged between 96 N and 169 N for Fmax, 0.017s and 0.055s for CT and 0.021s and 0.026s for FT. In conclusion, Zebris reliability was acceptable to excellent for the variables examined, but inferior in comparison with Pedar-X. With increased running speeds, a bias effect (underestimation) existed for the Zebris compared with Pedar-X.

Is Plantar Loading Altered During Repeated Sprints on Artificial Turf in International Football Players?

We compared fatigue-induced changes in plantar loading during the repeated anaerobic sprint test over two distinct distance intervals. Twelve international male football outfield players (Qatar Football Association) completed 6 × 35-m sprints (10 s of active recovery) on artificial turf with their football boots. Insole plantar pressure distribution was continuously recorded and values (whole foot and under 9 foot zones) subsequently averaged and compared over two distinct distance intervals (0-17.5 m vs. 17.5-35 m). Sprint times increased (p <0.001) from the first (4.87 ± 0.13 s) to the last (5.63 ± 0.31 s) repetition, independently of the distance interval. Contact area (150 ± 23 vs. 158 ± 19 cm2; -5.8 ± 9.1%; p = 0.032), maximum force (1910 ± 559 vs. 2211 ± 613 N; -16.9 ± 18.2%; p = 0.005) and mean pressure (154 ± 41 vs. 172 ± 37 kPa; -13.9 ± 19.0%; p = 0.033) for the whole foot were lower at 0-17.5 m vs. 17.5-35 m, irrespectively of sprint number. There were no main effects of sprint number or any significant interactions for any plantar variables of the whole foot. The distance interval × sprint number × foot region interaction on relative loads was not significant. Neither distance interval nor fatigue modified plantar pressure distribution patterns. Fatigue led to a decrement in sprint time but no significant change in plantar pressure distribution patterns across sprint repetitions.

Fifth metatarsal stress fracture in elite male football players: an on-field analysis of plantar loading.

OBJECTIVE: Evaluate plantar loading during 'on-field' common football movements in players after fifth metatarsal (MT-5) stress fracture and compare with matched healthy players. METHODS: Fourteen elite male soccer players participated in the study conducted on a natural grass playing surface using firm ground football boots. Seven players who had suffered a primary stress fracture (MT-5 group) and seven matched healthy players (controls, CON) performed three common football movements while in-shoe plantar loading data were collected. RESULTS: Large between-group differences exist for maximal vertical force normalised to bodyweight (Fmax) at the lateral toes (2-5) of the stance leg during a set-piece kick (MT-5: 0.2±0.06 bodyweight (BW), CON: 0.1±0.05 BW, effect size (ES) 1.4) and the curved run where the MT-5 group showed higher Fmax with very large effect size at the lateral forefoot of the injured (closest to curve) limb when running a curve to receive a pass (MT-5 injured-CON=0.01 BW, ES 1.5). Small between-group differences were evident during straight-line running. However, between-limb analysis of MT-5 group showed significant unloading of the lateral forefoot region of the involved foot. CONCLUSIONS: Elite male football players who have returned to play after MT-5 stress fracture display significantly higher maximum plantar force at the lateral forefoot and lateral toes (2-5) compared with healthy matched control players during two football movements (kick and curved run) with the magnitude of these differences being very large. These findings may have important implications for manipulating regional load during rehabilitation or should a player report lateral forefoot prodromal symptoms.

Marked asymmetry in vertical force (but not contact times) during running in ACL reconstructed athletes <9 months post-surgery despite meeting functional criteria for return to sport.

OBJECTIVES: Compare maximum plantar force (Fmax) during running in soccer players following anterior cruciate ligament reconstruction (ACLR) as they pass return to sport (RTS) criteria. DESIGN: Case control study. METHODS: Soccer players after ACLR (n=16) and matched healthy controls (n=16) ran on a treadmill at 12, 14 and 16km/h while plantar loading data was measured using an in-shoe pressure system (Pedar-X, Novel). Fmax and contact time of the injured and uninjured limbs in athletes <9months post-ACLR and those ≥9months ACLR were compared to healthy players (no ACLR). RESULTS: Significant differences with large effect sizes in Fmax asymmetry were seen at all running speeds for the athletes <9months ACLR compared to those ≥9months, and the healthy subjects. Fmax difference peaked at 16km/h; 32±11%BW in <9months ACLR group compared to 6±5%BW in ≥9months group; ES=1.67, p<0.01. There was a non-significant trend for increasing asymmetry with increasing speed for subjects who were <9months after ACLR while the reverse was true for those ≥9 months and the healthy subjects. CONCLUSIONS: Relatively large unloading of the ACLR limb (but not differences in contact times) are seen during running for athletes <9months post-ACLR despite having completed functional criteria required to permit RTS training. These asymmetries appear to slightly increase with increasing speed, and the reverse is true for healthy controls and those ≥9months after ACLR surgery.

Hyperthermia-induced Neural Alterations Impair Proprioception and Balance.

PURPOSE: Hyperthermia has been shown to affect both central and peripheral nervous systems. However, the consequences of these alterations on the proprioceptive mechanisms underlying human movement control remain unclear. The aim of this study was to investigate the effect of passive hyperthermia on various measures of proprioception and balance, two key components of injury prevention and movement efficiency. METHODS: After a familiarization session, 14 volunteers (8 males, 6 females) completed two experimental sessions in temperate (CON, 24°C) and hot (HOT, 44°C-50°C) conditions, in a counterbalanced order. Participants were tested for neural function (electrically evoked M-wave and Hoffman reflex, Soleus), active movement discrimination (five positions, 50 trials, dorsiflexion), dynamic balance (Star Excursion Balance Test, three directions), and static balance (single-leg stance). RESULTS: Both rectal (39.0°C ± 0.3°C vs 36.9°C ± 0.6°C) and mean skin (37.9°C ± 1.0°C vs 32.0°C ± 2.7°C) temperatures were significantly higher in HOT than CON (P < 0.05). Hyperthermia significantly reduced the Hoffman reflex (P < 0.05) but not the M-wave (P > 0.05) amplitudes, increased the mean error for active movement discrimination (0.58°± 0.13° vs 0.50° ± 0.11°, +17%, P < 0.05), decreased the average distance reached in the posteromedial direction during dynamic balance (88.6 ± 7.9 cm vs 90.9 ± 6.1 cm, P < 0.05), and increased the contact area of the foot (126 ± 14 cm vs 122 ± 13 cm, +2.7%, P < 0.05) and the center of pressure excursion (64 ± 14 vs 57 ± 9 cm, +11.1%, P < 0.10) during single-leg stance. CONCLUSIONS: The current study suggests that hyperthermia impairs the proprioception and balance parameters measured. These observations might be due to heat-induced alterations in efferent and afferent signals to and from the muscle.

Hamstring and calf muscle activation as a function of bodyweight support during treadmill running in ACL reconstructed athletes.

Rehabilitation after injury and reconstruction to the anterior cruciate ligament is thought to require a gradual reintroduction of loading, particularly during resumption of running. One strategy to achieve this is via the use of a reduced-gravity treadmill but it is unknown, if and how muscle activity varies in the reduced gravity conditions compared to regular treadmill running. Nineteen healthy participants and 18 male patients at the end of their rehabilitation (8 with a bone-patellar-bone graft, 10 with a hamstring graft) participated in this multi-muscle surface electromyography (sEMG) running study. The hamstrings and triceps surae were evaluated during a 16km/h running while at 6 different relative bodyweight conditions from 50% (half weight-bearing) to 100% (full weight-bearing). Muscle activation was examined individually as well as normalized to a composite "entire" activation and considered across the entire gait cycle using Statistical Parametric Mapping. The healthy participants showed differences between the 50-100% BW and 60-100% conditions and in the hamstring graft group for 60-100% and 80-100% conditions. No differences were seen comparing all loading conditions in the bone-patellar-bone graft group. For the hamstrings, from 70% BW and above, there appear to be no difference in activation patterns for any of the groups. The activation patterns of the hamstrings was essentially the same from 70% indicated bodyweight through to full weight bearing when running at 16km/h. Accordingly, when running at this relatively high speed, we do not expect any adverse effects in terms of altered motor patterns during rehabilitation of these muscles.

Peak medial (but not lateral) hamstring activity is significantly lower during stance phase of running. An EMG investigation using a reduced gravity treadmill.

The hamstrings are seen to work during late swing phase (presumably to decelerate the extending shank) then during stance phase (presumably stabilizing the knee and contributing to horizontal force production during propulsion) of running. A better understanding of this hamstring activation during running may contribute to injury prevention and performance enhancement (targeting the specific role via specific contraction mode). Twenty active adult males underwent surface EMG recordings of their medial and lateral hamstrings while running on a reduced gravity treadmill. Participants underwent 36 different conditions for combinations of 50%-100% altering bodyweight (10% increments) & 6-16km/h (2km/h increments, i.e.: 36 conditions) for a minimum of 6 strides of each leg (maximum 32). EMG was normalized to the peak value seen for each individual during any stride in any trial to describe relative activation levels during gait. Increasing running speed effected greater increases in EMG for all muscles than did altering bodyweight. Peak EMG for the lateral hamstrings during running trials was similar for both swing and stance phase whereas the medial hamstrings showed an approximate 20% reduction during stance compared to swing phase. It is suggested that the lateral hamstrings work equally hard during swing and stance phase however the medial hamstrings are loaded slightly less every stance phase. Likely this helps explain the higher incidence of lateral hamstring injury. Hamstring injury prevention and rehabilitation programs incorporating running should consider running speed as more potent stimulus for increasing hamstring muscle activation than impact loading.

Running speed increases plantar load more than per cent body weight on an AlterG® treadmill.

AlterG® treadmills allow for running at different speeds as well as at reduced bodyweight (BW), and are used during rehabilitation to reduce the impact load. The aim of this study was to quantify plantar loads borne by the athlete during rehabilitation. Twenty trained male participants ran on the AlterG® treadmill in 36 conditions: all combinations of indicated BW (50-100%) paired with different walking and running speeds (range 6-16 km · hr-1) in a random order. In-shoe maximum plantar force (Fmax) was recorded using the Pedar-X system. Fmax was lowest at the 6 km · hr-1 at 50% indicated BW condition at 1.02 ± 0.21BW and peaked at 2.31 ± 0.22BW for the 16 km · hr-1 at 100% BW condition. Greater increases in Fmax were seen when increasing running speed while holding per cent BW constant than the reverse (0.74BW-0.91BW increase compared to 0.19-0.31BW). A table is presented with each of the 36 combinations of BW and running speed to allow a more objective progression of plantar loading during rehabilitation. Increasing running speed rather than increasing indicated per cent BW was shown to have the strongest effect on the magnitude of Fmax across the ranges of speeds and indicated per cent BWs examined.

Higher shoe-surface interaction is associated with doubling of lower extremity injury risk in football codes: a systematic review and meta-analysis.

BACKGROUND: Turning or cutting on a planted foot may be an important inciting event for lower limb injury, particularly when shoe-surface traction is high. We systematically reviewed the relationship between shoe-surface interaction and lower-extremity injury in football sports. METHODS: A systematic literature search of four databases was conducted up to November 2014. Prospective studies investigating the relationship between rotational traction and injury rate were included. Two researchers independently extracted outcome data and assessed the quality of included studies using a modified Downs and Black index. Effect sizes (OR+95% CIs) were calculated using RevMan software. Where possible, data were pooled using the fixed effect model. RESULTS: Three prospective studies were included (4972 male athletes). The methodological quality was generally good with studies meeting 68-89% of the assessment criteria. All studies categorised athletes into low (lowest mean value 15 nm) or high traction groups (highest mean value 74 nm) based on standardised preseason testing. In all cases, injury reporting was undertaken prospectively over approximately three seasons, with verification from a medical practitioner. Injury data focused on: all lower limb injuries, ankle/knee injuries or ACL injury only. There was a clear relationship between rotational traction and injury and the direction and magnitude of effect sizes were consistent across studies. The pooled data from the three studies (OR=2.73, 95% CI 2.13 to 3.15; χ(2)=3.19, df=2, p=0.21; I(2)=36.5%) suggest that the odds of injury are approximately 2.5 times higher when higher levels of rotational traction are present at the shoe-surface interface. SUMMARY AND CONCLUSIONS: Higher levels of rotational traction influence lower limb injury risk in American Football athletes. We conclude that this warrants considerable attention from clinicians and others interested in injury prevention across all football codes.