Body mass affects kinetic symmetry and inflammatory markers in adolescent knees during gait.

BACKGROUND: Early-onset osteoarthritis has been attributed to pro-inflammatory factors and biomechanical changes in obesity. However, research has yet to explore whether knee joint moments are asymmetrical in children with obesity and could precede the onset of knee osteoarthritis. The present study compares knee moment asymmetry between adolescents with and without obesity and examines the relationship between asymmetries and inflammatory biomarkers. METHODS: Twenty-eight adolescents (13-16 years) were classified as with (n = 12) or without (n = 16) obesity. Lower extremity kinetics were measured using three-dimensional motion analysis. Bilateral knee joint moments were analyzed in the sagittal, frontal, and transverse planes across stance phase. Kinetic asymmetry was calculated between the right and left sides and represented by the R2 value. Enzyme-linked immunosorbent assays analyzed serum 25-hydroxy vitamin D, interferon gamma, tumor nercrosis factor alpha, interleukin-6, and C-reactive protein levels. Parametric and non-parametric tests determined significant group differences in asymmetries and biomarkers, respectively. Spearman's correlations identified relationships between biomarkers and asymmetries with statistically significant group differences. FINDINGS: Adolescents with obesity had greater sagittal (loading, midstance) and frontal (midstance, pre-swing) plane kinetic knee asymmetry and higher concentrations of interleukin-6 and C-reactive protein. A moderately negative correlation existed between C-reactive protein and sagittal (loading, midstance) plane asymmetry, and also between interleukin-6 and frontal (pre-swing) plane asymmetry. INTERPRETATION: Inflammatory response increases with greater knee joint asymmetry, suggesting knee joint damage and altered joint loading co-exist in adolescents with obesity. Increased risk to joint health may exist in sub-phases where knee joints are improperly loaded.

Using a modified vector coding technique to describe the calcaneus-shank coupling relationship during unanticipated changes of direction: theoretical implications for prophylactic ACL strategies.

Shank rotation is associated with increased risk in lower limb injuries of weight-bearing sport activity. Straight-line running injury prevention research proposes a 'bottom-up' approach to minimising injury risk to the knee. This prophylactic recommendation is due to the observed distal-proximal coupling relationship between rearfoot and shank rotations. However, the coupling relationship between the calcaneus and shank is unknown in sports with high intensity decelerations, frequent changes of direction, associated with increased anterior cruciate ligament (ACL) injury risk. The aim of this study was to determine whether the movement of the calcaneus has a potential effect on the internal and external rotational movement of the shank, associated with ACL injury risk. We implemented a modified vector coding technique using segmental velocities in a local, anatomical reference frame to quantify the coupling relationship between the individual tri-planar calcaneus rotations and transverse plane shank rotations. During the loading phase, a distal-proximal coupling relationship between calcaneus eversion deceleration, abduction acceleration, and shank internal rotation deceleration was observed amongst most subjects. The distal-proximal coupling found between the calcaneus and shank justifies exploring interventions geared towards manipulating calcaneus motion to affect shank rotational movements during unanticipated change of direction tasks associated with ACL injury risk.

Replacing Sedentary Time with Physically Active Behaviour Predicts Improved Body Composition and Metabolic Health Outcomes.

BACKGROUND: Discretionary leisure time for health-promoting physical activity (PA) is limited. This study aimed to predict body composition and metabolic health marker changes from PA reallocation using isotemporal substitution analysis. METHODS: Healthy New Zealand women (n = 175; 16-45 y) with high BMI (≥25 kg/m2) and high body fat percentage (≥30%) were divided into three groups by ethnicity (Maori n = 37, Pacific n = 54, and New Zealand European n = 84). PA, fat mass, lean mass, and metabolic health were assessed. Isotemporal substitution paradigms reallocated 30 min/day of sedentary behaviour to varying PA intensities. RESULTS: Reallocating sedentary behaviour with moderate intensity, PA predicted Maori women would have improved body fat% (14.83%), android fat% (10.74%), and insulin levels (55.27%) while the model predicted Pacific women would have improved waist-to-hip (6.40%) and android-to-gynoid (19.48%) ratios. Replacing sedentary time with moderate-vigorous PA predicted Maori women to have improved BMI (15.33%), waist circumference (9.98%), body fat% (16.16%), android fat% (12.54%), gynoid fat% (10.04%), insulin (55.58%), and leptin (43.86%) levels; for Pacific women, improvement of waist-to-hip-ratio (5.30%) was predicted. CONCLUSIONS: Sedentary behaviour must be substituted with PA of at least moderate intensity to reap benefits. Maori women received the greatest benefits when reallocating PA. PA recommendations to improve health should reflect the needs and current activity levels of specific populations.

Mini-Trampoline Jumping as an Exercise Intervention in Postmenopausal Women to Improve Women Specific Health Risk Factors.

BACKGROUND: Women tend to outlive men and are at higher risks of functional disability compared to men. Specifically, women are more likely to develop conditions like osteoporosis and stress urinary incontinence which can further increase the risk of functional disability. Regular physical activity and/or exercise programs can minimize the physiological decline that occurs during aging and can improve overall physical fitness, bone health, and pelvic floor muscle function; however, exercise programs tend to focus on only one parameter. Mini-trampoline jumping is a highly beneficial low-impact aerobic exercise capable of improving aerobic fitness, balance, muscle strength, and potentially bone health as well as pelvic floor muscle functioning. The aim of the proposed research project is to examine the benefits of a 3-month mini-trampoline exercise intervention on physical fitness, bone health, and pelvic floor muscle functioning in postmenopausal women. METHODS: Fifty postmenopausal healthy women aged 50-69 years will be recruited. Assessments on physical fitness (aerobic fitness, walking speed, balance, lower extremity strength, flexibility), bone health, and pelvic floor muscle functioning will occur within 1 week before and after the exercise intervention, including a 3-month follow-up assessment. The exercise intervention will last 12 weeks, with three sessions of 40 min each per week. CONCLUSIONS: The proposed research has the potential to improve functional ability and women-specific risk factors in older women with an innovative and fun exercise program.

Foot Muscle Strengthening and Lower Limb Injury Prevention.

Background and objectives: The active and passive structures of the foot act in unison to not only be compliant enough to assist in ground reaction force attenuation but also resist deformation to provide a stable base of support. A foot that is unable to adjust to the imposed demands during high-intensity sporting activities may alter the moments and forces acting on the joints, increasing the risk of non-contact anterior cruciate ligament ruptures (ACLR) and lateral ankle sprains (LAS). Prophylactic strengthening programs are often used to reduce the risk of these injuries, but at present, very few prophylactic programs include foot-specific strengthening strategies. The aim of this theoretical review is to ascertain the prophylactic role strengthening muscles acting on the foot may have on ACLR and LAS injury risk. Methods: Literature relating to risk factors associated with ACLR and LAS injury and the anatomy and biomechanics of normal foot function was searched. In addition, ACLR and LAS injury prevention programs were also sought. A theoretical, narrative approach was followed to synthesize the information gathered from the articles. Results: The foot segments are governed by the congruity of the articulations and the activity of the foot muscles. As such, there is a coupling effect between shank, calcaneus, midfoot, and hallux movement which play a role in both ACLR and LAS injury risk. Conclusions: Strengthening the muscles acting on the foot may have a significant impact on ACLR and LAS injury risk.

The coordination patterns of the foot segments in relation to lateral ankle sprain injury mechanism during unanticipated changes of direction.

Preventing lateral ankle sprain injuries (LAS) in females competing in court sports is a high priority, as an athlete's risk for re-injury and developing long term dysfunction increases significantly after sustaining an acute LAS. Stability to the ankle joint is passively provided by the joint congruity and ligaments, and actively by the muscles acting on the foot. The ankle joint is most stable when loaded and dorsiflexed. However, during unanticipated changes of direction, typical in court sports, the foot is often in a vulnerable unloaded, plantarflexed position. Stability of the forefoot and controlling rearfoot movement to avoid excessive ankle inversion and adduction thus becomes imperative. Information regarding the coupling relationship between the forefoot (hallux and metatarsal segments) and the rearfoot (calcaneus segment) during unanticipated changes of direction is lacking. The aim of this study was to supplement current LAS prophylactic knowledge by describing and quantifying hallux-calcaneus and metatarsal-calcaneus coupling. The coupling angles between sagittal plane hallux, tri-planar metatarsal and frontal- and transverse plane calcaneus movement, respectively, were calculated with a modified vector coding technique which used segmental velocities in a local, anatomical reference frame instead of segmental angles in a global reference frame. Coupling relationships revealed anti-phase movement between sagittal- metatarsal and frontal plane calcaneus movement throughout stance. During loading, sagittal- and frontal plane metatarsal acceleration/deceleration were coupled with frontal-transverse plane calcaneus acceleration/deceleration respectively. The remainder of the braking phase was characterized by calcaneus eversion deceleration. During propulsion, the hallux and metatarsal segments increased plantar flexion velocity in response to calcaneus inversion and adduction acceleration. As the forefoot was the only point of contact during stance, the coupling between segments were most likely neuromuscular. Strengthening intrinsic and extrinsic foot muscles may thus contribute to foot and ankle stability, adding to current prophylactic LAS strategies.

Age-Related Differences in Perceived Exertion While Walking and Running Near the Preferred Transition Speed.

PURPOSE: To investigate whether youth and adults can perceive differences in exertion between walking and running at speeds near the preferred transition speed (PTS) and if there are age-related differences in these perceptions. METHODS: A total of 49 youth (10-12 y, n = 21; 13-14 y, n = 10; 15-17 y, n = 18) and 13 adults (19-29 y) completed a walk-to-run transition protocol to determine PTS and peak oxygen uptake. The participants walked and ran on a treadmill at 5 speeds (PTS-0.28 m·s-1, PTS-0.14 m·s-1, PTS, PTS+0.14 m·s-1, PTS+0.28 m·s-1) and rated perceived exertion using the OMNI Perceived Exertion (OMNI-RPE) scale. Oxygen consumption was measured during the walk-to-run transition protocol to obtain the relative intensity (percentage of peak oxygen uptake) at PTS. OMNI-RPE scores at all speeds and percentage of peak oxygen uptake at PTS were compared between age groups. RESULTS: The 10- to 12-year-olds transitioned at a higher percentage of peak oxygen uptake than adults (64.54 [10.18] vs 52.22 [11.40], respectively; P = .035). The 10- to 14-year-olds generally reported higher OMNI-RPE scores than the 15- to 17-year-olds and adults (P < .050). In addition, the 10- to 14-year-olds failed to distinguish differences in OMNI-RPE between walking and running at PTS and PTS+0.14 m·s-1. CONCLUSIONS: Children aged 10-14 years are less able to distinguish whether walking or running requires less effort at speeds near the PTS compared with adults. The inability to judge which gait mode is less demanding could hinder the ability to minimize locomotive demands.

Are all Sedentary Behaviors Equal? An Examination of Sedentary Behavior and Associations with Indicators of Disease Risk Factors in Women.

Sedentary behavior increases risk for non-communicable diseases; associations may differ within different contexts (e.g., leisure time, occupational). This study examined associations between different types of sedentary behavior and disease risk factors in women, using objectively measured accelerometer-derived sedentary data. A validation study (n = 20 women) classified sedentary behavior into four categories: lying down; sitting (non-active); sitting (active); standing. A cross-sectional study (n = 348 women) examined associations between these classifications and disease risk factors (body composition, metabolic, inflammatory, blood lipid variables). Participants spent an average of 7 h 42 min per day in sedentary behavior; 58% of that time was classified as non-active sitting and 26% as active sitting. Non-active sitting showed significant (p ≤ 0.001) positive correlations with BMI (r = 0.244), body fat percent (r = 0.216), body mass (r = 0.236), fat mass (r = 0.241), leptin (r = 0.237), and negative correlations with HDL-cholesterol (r = -0.117, p = 0.031). Conversely, active sitting was significantly (p ≤ 0.001) negatively correlated with BMI (r = -0.300), body fat percent (r = -0.249), body mass (r = -0.305), fat mass (r = -0.320), leptin (r = -0.259), and positively correlated with HDL-cholesterol (r = 0.115, p = 0.035). In summary, sedentary behavior can be stratified using objectively measured accelerometer-derived activity data. Subsequently, different types of sedentary behaviors may differentially influence disease risk factors. Public health initiatives should account for sedentary classifications when developing sedentary behavior recommendations.

Improving Engagement With Biomechanics: Student Perspectives and a Professional Development Initiative.

Student engagement is an essential aspect of educational environments, and this is especially true for Science, Technology, Engineering, and Mathematics (STEM) disciplines, where student engagement declines in middle and high school years. Techniques for bolstering student engagement, such as hands-on learning, may be especially effective in the field of biomechanics since this discipline is rooted in STEM and has fundamental applications to everyday movement. To this end, this paper describes (1) the perceptions of student teachers in their first year of tertiary (undergraduate) education regarding the biomechanics content from their secondary (high school) education, and (2) a professional development initiative, in the form of a discipline-specific teacher training workshop, to enhance biomechanics resources for teachers via peer networking. The perception of student teachers in their first year of tertiary education in teaching indicated a positive relationship between perception of secondary school teaching quality and self-confidence with specific biomechanical concepts. Open responses focused on the need to cover concepts thoroughly, using practical activities where possible, and taking time to ensure understanding before progressing to more advanced concepts. The teacher training workshop provided secondary school Physical Education teachers with an opportunity to network nationally with other teachers across New Zealand, and internationally with university-based biomechanics researchers. Peer focus groups helped to design and refine sets of experiential learning activities that could be easily implemented in the classroom.

Age-dependent variability in spatiotemporal gait parameters and the walk-to-run transition.

Adolescents tend to exhibit more variability in their gait patterns than adults, suggesting a lack of gait maturity during this period of ongoing musculoskeletal growth and development. However, there is a lack of consensus over the age at which mature gait patterns are achieved and the factors contributing to gait maturation. Therefore, the purpose of this study was to investigate gait control and maturity in adolescents by determining if differences existed between adolescents and adults in a) the amount of spatiotemporal variability of walking and running patterns across a range of speeds, and b) how swiftly gait patterns are adapted to increasing gait speed during the walk-to-run transition. Forty-six adolescents (10-12-year-olds, n = 17; 13-14-year-olds, n = 12; and 15-17-year-olds, n = 17) and 12 young adults completed an incrementally ramped treadmill test (+0.2 km·h-1 every 30 s) to determine the preferred transition speed (PTS) during a walk-to-run transition. Age-related differences in the variability of stride lengths and stride durations were assessed across 4 speeds (self-selected walking speed, PTS - 0.06 m·s-1, PTS + 0.06 m·s-1, PTS + 0.83 m·s-1). Repeated measures ANOVAs (p < 0.05) compared coefficients of variation for these spatiotemporal parameters, while a one-way ANOVA compared the numbers of gait transitions and speed increments used to identify PTS between the adolescent groups and young adults. Compared to adults, 10-12yo exhibited more spatiotemporal variability during all gait conditions, while 13-17yo only exhibited more variability at PTS + 0.06 m·s-1. No age-dependent pattern was observed in PTS values, but 10-12yo completed more gait transitions over more speed increments than 15-17yo and adults. The development of mature gait patterns is thus a progressive process, with walking maturing at an earlier age than running. As 10-12yo were unable to swiftly adapt gait patterns to the changing task demands, their control mechanisms of gait may not have fully matured yet.

Kinematic Comparison of Aquatic- and Land-Based Stationary Exercises in Overweight and Normal Weight Children.

PURPOSE: This study examined lower extremity kinematics in healthy weight (HW) and overweight (OW) children during water- and land-based stationary exercises (stationary running, frontal kick, and butt kick) at light submaximal intensity. METHODS: Participants included OW (N = 10; body fat percentage: 34.97 [8.60]) and HW (N = 15; body fat percentage: 18.33 [4.87]) children, aged 10 to 13 years. Spatiotemporal data, lower extremity joint kinematics, and rating of perceived exertion (RPE) were collected during water- and land-based stationary exercises. Repeated measures analysis of variance compared kinematic variables and RPE between groups and environments. A polygon area function compared coordination patterns between environments. RESULTS: RPE responses were significantly greater in OW than HW children on land (13.6 [0.7] vs 11.6 [0.7]; P < .001), whereas the RPE responses were similar between groups in water (11.2 [0.7] vs 11.1 [0.8]; P > .05). OW children were significantly more upright than HW children during land-based exercise, whereas there were no differences observed between groups during aquatic-based exercise. The duration of stance and swing phases, angular velocity, and cadence were significantly lower in water than on land. CONCLUSION: Compared with HW children, OW children performed stationary exercises in a more upright posture on land, with higher RPE. However, these differences diminished in water. Aquatic-based exercise may be effective in minimizing the effects of excess mass on OW children's ability to complete physical activity.

Lower extremity muscle function of front row rugby union scrummaging.

A rugby scrum's front row must act uniformly to transfer maximal horizontal force and improve performance. This study investigated the muscle activation patterns of lower extremity muscles in front row forwards during live and machine scrums at professional and amateur levels. Electromyography was collected bilaterally on vastus lateralis, rectus femoris and gastrocnemius muscles of 75 male rugby prop players during live and machine scrums. ANOVAs compared muscle reaction time, rate of change in muscle amplitude and muscle amplitude between groups and conditions. Cross-correlation analysis explored muscle synchronicity. There were significantly greater rates of change in each muscle amplitude in professional players than amateur players. Additionally, there was significantly quicker muscle reaction time in all muscles, and greater amplitude in vastus lateralis and gastrocnemius, during the live scrum vs. machine condition. The professional props produced more synchronised muscle activation than amateur players and all players produced more synchronised muscle activation against the scrum machine vs. live scrummage. The results indicate a higher skill proficiency and muscle synchronicity in professional players. While scrum machine training is ideally suited for functional muscle strengthening during practice, to truly simulate the requirements of the scrum, training should incorporate the live situation as much as possible.

Quantification of brake data acquired with a brake power meter during simulated cross-country mountain bike racing.

There is currently a dearth of information describing cycling performance outside of propulsive and physiological variables. The aim of the present study was to utilise a brake power meter to quantify braking during a multi-lap cross-country mountain bike time trial and to determine how braking affects performance. A significant negative association was determined between lap time and brake power (800.8 ± 216.4 W, mean ± SD; r = -0.446; p < 0.05), while the time spent braking (28.0 ± 6.4 s) was positively associated with lap time (314.3 ± 37.9 s; r = 0.477; p < 0.05). Despite propulsive power decreasing after the first lap (p < 0.05), lap time remained unchanged (p > 0.05) which was attributed to decreased brake work (p < 0.05) and brake time (p < 0.05) in both the front and rear brakes by the final lap. A multiple regression model incorporating braking and propulsion was able to explain more of the variance in lap time (r2 = 0.935) than propulsion alone (r2 = 0.826). The present study highlights that riders' braking contributes to mountain bike performance. As riders repeat a cross-country mountain bike track, they are able to change braking, which in turn can counterbalance a reduction in power output. Further research is required to understand braking better.

Multifractal Analysis Differentiates Postural Sway in Obese and Nonobese Children.

Multifractal analyses have been used in recent years as a way of studying balance, with the goal of understanding the patterns of movement of the center of pressure at different spatial scales. A multifractal detrended fluctuation analysis was used to compare obese and nonobese children to investigate the cause of previously demonstrated deficiencies in balance for obese children. Twenty-two children (11 obese and 11 nonobese), aged 8-15 years, performed 30-s trials of bilateral static balance on a plantar pressure distribution measuring device. Both the obese and nonobese groups demonstrated greater persistence for small fluctuations, but the effect was greater in the obese group. This was particularly evident with the eyes closed, where significant differences between the obese and nonobese were observed for small fluctuations. These results demonstrate that balance deficiencies in obese children may be the result of decreased proprioceptive abilities in obese children.

Stationary Exercise in Overweight and Normal Weight Children.

PURPOSE: This study examined differences in lower extremity kinematics and muscle activation patterns between normal weight (NW) and overweight (OW) children during stationary exercises (running in place, frontal kick, and butt kick) at submaximal intensity. METHODS: Healthy children (aged 10-13 y) were stratified into OW (n = 10; body fat percentage: 34.97 [8.60]) and NW (n = 15; body fat percentage: 18.33 [4.87]). Electromyography was recorded for rectus femoris, vastus lateralis, biceps femoris, gastrocnemius, and tibialis anterior. In addition, the ratings of perceived exertion and range of motion of hip, knee, and ankle joints were collected during stationary exercises. Repeated-measures analysis of variance compared muscle activation, range of motion, and ratings of perceived exertion between groups and exercises. Friedman test examined sequencing of muscles recruitment. RESULTS: Compared with NW, OW experienced significantly greater ratings of perceived exertion (13.7 [0.8] vs 11.7 [0.7]; P < .001) and electromyography amplitude in all muscles apart from vastus lateralis during stationary exercises. In addition, NW children used more consistent muscles' recruitment pattern in comparison with OW children. The range of motion was similar between groups at all joints. CONCLUSION: OW children may adopt a more active neuromuscular strategy to provide greater stability and propulsion during stationary exercises. Stationary exercise can be prescribed to strengthen lower extremity muscles in OW children, but mode and intensity must be considered.

The Effects of Uniquely-Processed Titanium on Balance and Walking Performance in Healthy Older Adults.

The increased risk of falls associated with advancing age has increased demand for methods to improve balance and mobility. The primary purpose of the study was to determine whether wearing Aqua Titan-treated stockings could improve balance and walking performance in an older population; secondary was to elucidate the mechanisms. In a randomized, double-blind crossover, 16 healthy older adults (age, 67.9 ± 4.2 years; BMI, 24.8 ± 3.1 kg/m²) performed two 4-day trials composed of baseline measures and fatiguing exercise on Day 1, with recovery measures at 14, 38 and 62 h post-exercise, wearing Aqua Titan and control stockings. Balance, walking performance, triceps surae stretch reflex, ankle range of motion and gastrocnemius muscle microvascular perfusion, blood flow and oxygen consumption were measured at baseline and during recovery. Aqua Titan had no effect on the microvascular parameters, but increased total ankle range of motion at 38 h (2.4°; 95% CI ± 1.8°) and 62 h (2.7°; ±1.7°), contributed to by increases in dorsiflexion and plantar flexion. There was decreasing persistence in the medial-lateral center of pressure movement at 38 h (q = 0, −0.0635 ± 0.0455), compared to control stockings. Aqua Titan garments hold potential for improving balance and mobility in older adults in the days following a bout of fatiguing exercise. The proposed mechanisms associated with enhanced sensory feedback require further exploration.

What factors determine the preferred gait transition speed in humans? A review of the triggering mechanisms.

Human locomotion is a fundamental skill that is required for daily living, yet it is not completely known how human gait is regulated in a manner that seems so effortless. Gait transitions have been analyzed to gain insight into the control mechanisms of human locomotion since there is a known change that occurs as the speed of locomotion changes. Specifically, as gait speed changes, there is a spontaneous transition between walking and running that occurs at a particular speed. Despite the growing body of research on the determinants of this preferred transition speed and thus the triggering mechanisms of human gait transitions, a clear consensus regarding the control mechanisms of gait is still lacking. Therefore, this article reviews the determinants of the preferred transition speed using concepts of the dynamic systems theory and how these determinants contribute to four proposed triggers (i.e. metabolic efficiency, mechanical efficiency, mechanical load and cognitive and perceptual) of human gait transitions. While individual anthropometric and strength characteristics influence the preferred transition speed, they do not act to trigger a gait transition. The research has more strongly supported the mechanical efficiency and mechanical load determinants as triggering mechanisms of human gait transitions. These mechanical determinants, combined with cognitive and perceptual processes may thus be used to regulate human gait patterns through proprioceptive and perceptual feedback as the speed of locomotion changes.

Validity of a device designed to measure braking power in bicycle disc brakes.

Real-world cycling performance depends not only on exercise capacities, but also on efficiently traversing the bicycle through the terrain. The aim of this study was to determine if it was possible to quantify the braking done by a cyclist in the field. One cyclist performed 408 braking trials (348 on a flat road; 60 on a flat dirt path) over 5 days on a bicycle fitted with brake torque and angular velocity sensors to measure brake power. Based on Newtonian physics, the sum of brake work, aerodynamic drag and rolling resistance was compared with the change in kinetic energy in each braking event. Strong linear relationships between the total energy removed from the bicycle-rider system through braking and the change in kinetic energy were observed on the tar-sealed road (r2 = 0.989; p < 0.0001) and the dirt path (r2 = 0.952; p < 0.0001). T-tests revealed no difference between the total energy removed and the change in kinetic energy on the road (p = 0.715) or dirt (p = 0.128). This study highlights that brake torque and angular velocity sensors are valid for calculating brake power on the disc brakes of a bicycle in field conditions. Such a device may be useful for investigating cyclists' ability to traverse through various terrains.

The effectiveness of front fork systems at damping accelerations during isolated aspects specific to cross-country mountain biking.

Cross-country mountain bike suspension reportedly enhances comfort and performance through reduced vibration and impact exposure. This study analysed the effectiveness of three different front fork systems at damping accelerations during the crossing of three isolated obstacles (stairs, drop, and root). One participant completed three trials on six separate occasions in a randomised order using rigid, air-sprung, and carbon leaf-sprung forks. Performance was determined by time to cross obstacles, while triaxial accelerometers quantified impact exposure and damping response. Results identified significant main effect of fork type for performance time (p < 0.05). The air-sprung and leaf-sprung forks were significantly slower than the rigid forks for the stairs (p < 0.05), while air-sprung suspension was slower than the rigid for the root protocol (p < 0.05). There were no differences for the drop protocol (p < 0.05). Rigid forks reduced overall exposure (p < 0.05), specifically at the handlebars for the stairs and drop trials. More detailed analysis presented smaller vertical accelerations at the handlebar for air-sprung and leaf-sprung forks on the stairs (p < 0.05), and drop (p < 0.05) but not the root. As such, it appears that the suspension systems tested were ineffective at reducing overall impact exposure at the handlebar during isolated aspects of cross-country terrain features which may be influenced to a larger extent by rider technique.

Water depth effects on impact loading, kinematic and physiological variables during water treadmill running.

PURPOSE: The purpose of this study was to compare impact loading, kinematic and physiological responses to three different immersion depths (mid-shin, mid-thigh, and xiphoid process) while running at the same speed on a water based treadmill. METHODS: Participants (N=8) ran on a water treadmill at three depths for 3min. Tri-axial accelerometers were used to identify running dynamics plus measures associated with impact loading rates, while heart rate data were logged to indicate physiological demand. RESULTS: Participants had greater peak impact accelerations (p<0.01), greater impact loading rates (p<0.0001), greater stride frequency (p<0.05), shorter stride length (p<0.01), and greater rate of acceleration development at toe-off (p<0.0001) for the mid-shin and mid-thigh compared to running immersed to the xiphoid process. Physiological effort determined by heart rate was also significantly less (p<0.0001) when running immersed to the xiphoid process. CONCLUSION: Water immersed treadmill running above the waistline alters kinematics of gait, reduces variables associated with impact, while decreasing physiological demand compared to depths below the waistline.