Sensory enhancement of warm-up amplifies subsequent grip strength and cycling performance.

PURPOSE: In sport and exercise, warm-ups induce various physiological changes that facilitate subsequent performance. We have shown that delivering patterned stimulation to cutaneous afferents during sprint cycling mitigates fatigue-related decrements in performance, and that repeated sensory stimulation amplifies spinal reflex excitability. Therefore, the purpose of this study was to assess whether sensory enhancement of warm-up would affect subsequent high-intensity arm cycling performance. METHODS: Participants completed three experimental sessions, in which they randomly performed either a control, stim, or sleeve warm-up condition prior to maximal duration arm cycling. During the control condition, warmup consisted of low-intensity arm cycling for 15 min. The stim condition was the same, except they received alternating pulses (400 ms, 50 Hz) of stimulation just above their perceptual threshold to the wrists during warm-up. The third condition required participants to wear custom fabricated compression sleeves around the elbow during warm-up. Grip strength and spinal reflex excitability were measured before and after each warm-up and fatigue protocol, which required participants to arm cycle at 85% of peak power output until they reached volitional fatigue. Peak power output was determined during an incremental test at minimum 72 h prior to the first session. RESULTS: Both sensory enhanced warm-up conditions amplified subsequent high-intensity arm cycling performance by ~ 30%. Additionally, the stim and sleeve warm-up conditions yielded improvements in grip strength (increased by ~ 5%) immediately after the sensory enhanced warm-ups. Ergogenic benefits from the sensory enhanced warm-up conditions did not differ between one another. CONCLUSION: These findings demonstrate that enhanced sensory input during warm-up can elicit improvements in both maximal and submaximal performance measures.

Compression socks enhance sensory feedback to improve standing balance reactions and reflex control of walking.

BACKGROUND: Compression garments are generally used for their potential benefits in exercise performance and post-exercise recovery. Previous studies show that compression sleeves worn at the elbow change neuromuscular control and improve performance during reaching movement. Cutaneous stimulation of the foot skin produces location-specific reflexes in the lower limb that guide foot placement during locomotion. However, it is not clear whether enhancement of sensory feedback with compression socks can alter the neuromuscular excitability of muscles in the leg and amplify balance performance and walking. The current project aimed to determine whether enhanced sensory input from wearing compression socks could affect: 1) spinal cord excitability (as measured by cutaneous reflexes from stimulation at the top or bottom of the foot during locomotion); 2) static balance performance; and, 3) dynamic balance performance following virtual perturbations. METHODS: Twelve participants completed walking and balance tasks wearing four types of garments: 1) non-compression (control) socks; 2) ankle compression socks; 3) calf-compression socks; and, 4) customized ankle sleeves. During walking, electrical stimulations were delivered to three discrete locations on the dorsal (ankle crease, forefoot medial) and plantar (forefoot medial) surfaces of the foot in separate trials with each garment. Electromyography of ankle dorsiflexor tibialis anterior, plantarflexor medial gastrocnemius and evertor peroneus longus were measured bilaterally along with kinematic data from knee and ankle and kinetics under the right (stimulated) foot. RESULTS: Compared to control socks, altered cutaneous reflexes and biomechanical responses were observed in all the conditions during walking. In dynamic balance tests, time and integrated EMG for recovering from virtual perturbation were significantly reduced when wearing calf compression socks and the ankle sleeve. CONCLUSIONS: Our findings suggest sensory enhancement from compression garments modifies spinal cord excitability during walking and improves performance in balance recovery after virtual perturbation.

Effects of a compression garment on sensory feedback transmission in the human upper limb.

Compression apparel is popular in both medical and sport performance settings. Perceived benefits are suggested to include changes in sensory feedback transmission caused by activation of mechanoreceptors. However, little is known about effects of compression apparel on sensorimotor control. Our purpose was to mechanistically examine whether compression apparel modulates sensory feedback transmission and reaching accuracy in the upper limb. Two experiments were completed under CONTROL and COMPRESSION (sleeve applied across the elbow joint) conditions. M-waves and H-reflexes were elicited by stimulating the median nerve and were recorded via surface electromyography (EMG). In experiment 1, H-reflexes and M-H recruitment curves were assessed at REST, during wrist flexion (10% EMGmax), and during a cutaneous conditioning of the superficial radial (SR) or distal median (MED) nerve. Cutaneous reflexes were elicited during 10% wrist flexion via stimulation of SR or MED. In experiment 2, unconditioned H-reflex measures were assessed at rest, during arm cycling, and during a discrete reaching task. Results indicate that compression apparel modulates spinal cord excitability across multiple sensory pathways and movement tasks. Interestingly, there was a significant improvement in reaching accuracy while wearing the compression sleeve. Taken together, the compression sleeve appears to increase precision and sensitivity around the joint where the sleeve is applied. Compression apparel may function as a "filter" of irrelevant mechanoreceptor information allowing for optimal task-related sensory information to enhance proprioception. NEW & NOTEWORTHY Wearing a customized compression sleeve was shown to alter the excitability of multiple pathways within the central nervous system regardless of conditioning input or movement task and was accompanied by improved accuracy of reaching movements and determination of movement end point. Compression apparel may assist as a type of "filter function" of tonic and nonspecific mechanoreceptor information leading to increased precision and movement sensitivity around the joint where compression is applied.

Beyond the Bottom of the Foot: Topographic Organization of the Foot Dorsum in Walking.

INTRODUCTION: Sensory feedback from the foot dorsum during walking has only been studied globally by whole nerve stimulation. Stimulating the main nerve innervating the dorsal surface produces a functional stumble corrective response that is phase-dependently modulated. We speculated that effects evoked by activation of discrete skin regions on the foot dorsum would be topographically organized, as with the foot sole. METHODS: Nonnoxious electrical stimulation was delivered to five discrete locations on the dorsal surface of the foot during treadmill walking. Muscle activity from muscles acting at the ankle, knee, hip, and shoulder were recorded along with ankle, knee, and hip kinematics and kinetic information from forces under the foot. All data were sorted on the basis of stimulus occurrence in 12 step cycle phases, before being averaged together within a phase for subsequent analysis. RESULTS: Results reveal dynamic changes in reflex amplitudes and kinematics that are site specific and phase dependent. Most responses from discrete sites on the foot dorsum were seen in the swing phase suggesting function to conform foot trajectory to maintain stability of the moving limb. In general, responses from lateral stimulation differed from medial stimulation, and effects were largest from stimulation at the distal end of the foot at the metatarsals; that is, in anatomical locations where actual impact with an object in the environment is most likely during swing. Responses to stimulation extend to include muscles at the hip and shoulder. CONCLUSIONS: We reveal that afferent feedback from specific cutaneous locations on the foot dorsum influences stance and swing phase corrective responses. This emphasizes the critical importance of feedback from the entire foot surface in locomotor control and has application for rehabilitation after neurological injury and in footwear development.

Higher anterior knee laxity influences the landing biomechanics displayed by pubescent girls.

Despite an increase in anterior knee laxity (AKL) during the adolescent growth spurt in girls, it is unknown whether landing biomechanics are affected by this change. This study investigated whether pubescent girls with higher AKL displayed differences in their lower limb strength or landing biomechanics when performing a horizontal leap movement compared to girls with lower AKL. Forty-six pubescent girls (10-13 years) were tested at the time of their peak height velocity (PHV). Passive AKL was quantified and used to classify participants into higher (HAKL; peak displacement > 4 mm) and lower (LAKL; peak displacement < 3 mm) AKL groups (n = 15/group). Three-dimensional kinematics, ground reaction forces (GRF) and muscle activation patterns were assessed during a horizontal leap landing. HAKL participants displayed significantly (P < 0.05) reduced hip abduction, increased hip abduction moments, as well as earlier hamstring muscle and later tibialis anterior activation compared to LAKL participants. Girls with HAKL displayed compensatory landing biomechanics, which are suggested to assist the functional stability of their knees during this dynamic task. Further research is warranted, however, to confirm or refute this notion.

Spinal Cord Excitability and Sprint Performance Are Enhanced by Sensory Stimulation During Cycling.

Spinal cord excitability, as assessed by modulation of Hoffmann (H-) reflexes, is reduced with fatiguing isometric contractions. Furthermore, spinal cord excitability is reduced during non-fatiguing arm and leg cycling. Presynaptic inhibition of Ia terminals is believed to contribute to this suppression of spinal cord excitability. Electrical stimulation to cutaneous nerves reduces Ia presynaptic inhibition, which facilitates spinal cord excitability, and this facilitation is present during arm cycling. Although it has been suggested that reducing presynaptic inhibition may prolong fatiguing contractions, it is unknown whether sensory stimulation can alter the effects of fatiguing exercise on performance or spinal cord excitability. Thus, the aim of this experiment was to determine if sensory stimulation can interfere with fatigue-related suppression of spinal cord excitability, and alter fatigue rates during cycling sprints. Thirteen participants randomly performed three experimental sessions that included: unloaded cycling with sensory stimulation (CONTROL + STIM), sprints with sensory stimulation (SPRINT + STIM) and sprints without stimulation (SPRINT). Seven participants also performed a fourth session (CONTROL), which consisted of unloaded cycling. During SPRINT and SPRINT + STIM, participants performed seven, 10 s cycling sprints interleaved with 3 min rest. For CONTROL and CONTROL + STIM, participants performed unloaded cycling for ~30 min. During SPRINT + STIM and CONTROL + STIM, participants received patterned sensory stimulation to nerves of the right foot. H-reflexes and M-waves of the right soleus were evoked by stimulation of the tibial nerve at multiple time points throughout exercise. Sensory stimulation facilitated soleus H-reflexes during unloaded cycling, whereas sprints suppressed soleus H-reflexes. While receiving sensory stimulation, there was less suppression of soleus H-reflexes and slowed reduction in average power output, compared to sprints without stimulation. These results demonstrate that sensory stimulation can substantially mitigate the fatiguing effects of sprints.

How Young Girls Change Their Landing Technique Throughout the Adolescent Growth Spurt.

BACKGROUND: Despite the rapid musculoskeletal changes experienced by girls throughout the adolescent growth spurt, little is known about how their lower limb landing technique changes during this time. PURPOSE: To investigate the longitudinal changes in the 3-dimensional lower limb kinematics, joint moments, and muscle activation patterns displayed by girls when performing a horizontal landing task throughout their adolescent growth spurt. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 33 healthy 10- to 13-year-old girls, in Tanner stage II, with a maturity offset of -6 to -4 months (time from peak height velocity) were recruited. According to her maturity offset, each participant was tested up to 4 times during the 12 months of her growth spurt (maturity offset: test 1 = -6 to -4 months; test 2 = 0 months; test 3 = 4 months; test 4 = 8 months). During each test session, participants performed a horizontal leap movement, during which ground-reaction forces (1000 Hz), lower limb muscle activity (1000 Hz), and kinematic data (100 Hz) were collected. RESULTS: Throughout the growth spurt, girls displayed a decrease in knee flexion (P = .028), increase in hip flexion (P = .047), increase in external knee abduction moments (P = .008), and decrease in external hip adduction moments (P = .003) during the landing movement. CONCLUSION: During their adolescent growth spurt, pubescent girls displayed a change in the strategy with which they controlled their lower limb to land after performing a horizontal leap movement. This change in the landing strategy has the potential to increase the risk of anterior cruciate ligament injuries toward the latter stages of the adolescent growth spurt. CLINICAL RELEVANCE: The outcomes of this research provide a greater understanding of the changes in the landing strategy used by pubescent girls throughout the adolescent growth spurt. This can assist in the development of screening tools designed to determine "at-risk" landing biomechanics during puberty.

Perceived exercise barriers explain exercise participation in Australian women treated for breast cancer better than perceived exercise benefits.

OBJECTIVES: This study aimed to determine the effect of perceived exercise benefits and barriers on exercise levels among women who have been treated for breast cancer and have not participated in a formal exercise intervention. DESIGN: This was an anonymous, national, online cross-sectional survey study. METHODS: Four hundred thirty-two women treated for breast cancer completed an online survey covering their treatment and demographic background, current exercise levels, and perceived exercise benefits and barriers. Each perceived benefit and barrier was considered in a binary logistic regression against reported exercise levels to ascertain significant relationships and associative values (odds ratio [OR]). RESULTS: Agreement with 16 out of 19 exercise barriers was significantly related to being more likely to report insufficient exercise levels, whereas agreement with 6 out of 15 exercise benefits was significantly related to being less likely to report insufficient levels of exercise. Feeling too weak, lacking self-discipline, and not making exercise a priority were the barriers with the largest association to insufficient exercise levels (OR=10.97, 95% confidence interval [CI]=3.90, 30.86; OR=8.12, 95% CI=4.73, 13.93; and OR=7.43, 95% CI=3.72, 14.83, respectively). Conversely, exercise enjoyment, improved feelings of well-being, and decreased feelings of stress and tension were the top 3 benefits associated with being less likely to have insufficient exercise levels (OR=0.21, 95% CI=0.11, 0.39; OR=0.21, 95% CI=0.07, 0.63; and OR=0.31, 95% CI=0.15, 0.63, respectively). LIMITATIONS: Self-reported data measures were used to collect exercise data. CONCLUSIONS: Targeting exercise barriers specific to women treated for breast cancer may improve exercise participation levels in this cohort. Awareness of the impact of exercise barriers identified in the present study will enable physical therapists to better plan exercise interventions that support all women treated for breast cancer.

Evidence-based recommendations for building better bras for women treated for breast cancer.

Participating in exercise is beneficial for women who have been treated for breast cancer. However, not being able to find a comfortable exercise bra can be a barrier to exercise participation. This study aimed to systematically investigate what breast support women treated for breast cancer want when they exercise in order to provide evidence-based recommendations to improve exercise bra designs for these women. Based on 432 responses from a national online survey, frequency and relationship data were analysed (binary logistic regression) to understand exercise bra issues pertinent to this population. These issues included being able to control for asymmetrical cup sizes, managing heightened skin sensitivity, managing fluid (size) fluctuations, managing a prosthesis and restoring body image by restoring shape. This study provides evidence-based recommendations to inform an exercise bra design that will meet the unique needs of women treated for breast cancer. Rigorous, evidence-based evaluations of exercise bras for women treated for breast cancer may contribute to their well-being and quality of life through enhanced designs.

Sex differences in neuromuscular recruitment are not related to patellar tendon load.

PURPOSE: Although male volleyball players report a greater prevalence of patellar tendinopathy than female players, it remains unknown whether higher patellar tendon loading generated during landing by male players is related to sex-specific neuromuscular recruitment patterns. This study aimed to investigate the relationship between neuromuscular recruitment patterns and patellar tendon loading during landing and to determine whether there were any significant differences in lower limb neuromuscular recruitment patterns displayed by male and female volleyball players during landing. METHODS: The neuromuscular recruitment patterns and patellar tendon loading of 20 male and 20 female volleyball players performing a lateral stop-jump block movement were recorded and calculated. Pearson product-moment correlations were conducted to determine whether neuromuscular recruitment patterns were related to the peak patellar tendon force or patellar tendon force loading rate generated at landing. Independent t-tests were applied to a subset of data for 13 males and 13 females matched for jump height to identify any between-sex differences in neuromuscular recruitment patterns. RESULTS: Later onset of rectus femoris (r = 0.312), vastus medialis (r = 0.455), and biceps femoris (r = 0.330) were significantly correlated with a higher patellar tendon force loading rate, although these correlation values were weak. Male volleyball players displayed significantly earlier biceps femoris and semitendinosus onset, and significantly earlier peak semitendinosus activity compared with their female counterparts. CONCLUSION: Although male and female volleyball players displayed significantly different muscle onset times, these patterns were not strongly related to patellar tendon loading at landing. It is likely that a multitude of factors, including the frequency of patellar tendon loading, more strongly contributes to developing patellar tendinopathy than neuromuscular recruitment patterns in isolation.

Exercise bra discomfort is associated with insufficient exercise levels among Australian women treated for breast cancer.

PURPOSE: Although participating in exercise is beneficial for breast cancer survivors, not being able to find a comfortable exercise bra can be a barrier to exercise. It is likely that side effects specific to breast cancer treatment exacerbate exercise bra discomfort. This study aimed to determine the relationship between patient characteristics, physical side effects, exercise bra discomfort and exercise behaviours. METHODS: Four hundred thirty-two breast cancer survivors completed an online survey related to their treatment and demographic background, current exercise levels, reported exercise bra discomfort and breast cancer treatment side effects. Patient characteristics and exercise levels were considered in a binary logistic regression against reporting bra discomfort to ascertain significant relationships (p < 0.05) and predictive value (odds ratio). Pearson's chi-square statistics was used to determine significant relationships between reporting a side effect and exercise bra discomfort. RESULTS: Eight out of nine physical side effects were significantly related to reporting exercise bra discomfort. Reporting exercise bra discomfort was significantly related to not achieving a minimal recommended level of exercise. CONCLUSIONS: This is the first study in the scientific literature that systematically links the reporting of exercise bra discomfort to not achieving recommended levels of exercise. This effect of bra discomfort on exercise was found after controlling for age, surgery type and current treatment among a large cohort of women treated for breast cancer. Furthermore, results from this study suggest that physical side effects, as a result of surgery and treatment associated with breast cancer, are linked to experiencing bra discomfort during exercise.

Physiological cross-sectional area of the oblique head of the adductor pollicis is greater than its transverse counterpart: implications for functional testing.

INTRODUCTION: Despite structural distinction between the transverse and oblique heads of the adductor pollicis, in vivo testing continues to consider the adductor pollicis as functionally simplistic. As a muscle's architecture is a strong indicator of function, in this study we aimed to determine whether the physiological cross-sectional areas (PCSAs) of both heads were uniform. METHODS: Classical, microdissection, and chemical dissection procedures were conducted on 10 cadaveric left hands to determine structural origin and insertions. Architectural measures of muscle length (Lm ), muscle weight (Wm ), fascicle length (Lf ), sarcomere length (Ls ), and pennation angle (θ) were used to calculate PCSA and fascicle length:muscle length ratio (Lf :Lm ). RESULTS: The oblique head had greater variation in attachments, significantly greater PCSA (P = 0.008), and smaller Lf :Lm (P = 0.001) than its transverse counterpart. CONCLUSIONS: Muscle architecture suggests the oblique head has greater potential for force generation, and the transverse has greater potential for joint excursion.

Can technique modification training reduce knee moments in a landing task?

Anterior cruciate ligament (ACL) injuries are costly. Sidestep technique training reduces knee moments that load the ACL. This study examined whether landing technique training alters knee moments. Nineteen team sport athletes completed the study. Motion analysis and ground reaction forces were recorded before and after 6 weeks of technique modification. An inverse dynamic model was used to calculate three-dimensional knee loading. Pre- and postintervention scores were compared using paired t tests. Maximal knee flexion angle during landing was increased following training. There was no change in valgus or flexion moments, but an increase in peak internal rotation moment. This increase in internal rotation moment may increase the risk of ACL injury. However, the increased angle at which the peak internal rotation moment occurred at follow up may mitigate any increase in injury risk by reducing load transmission.

Self-reported side effects of breast cancer treatment: a cross-sectional study of incidence, associations, and the influence of exercise.

PURPOSE: Side effects as a result of breast cancer treatment may have a lasting detrimental impact on quality of life. Exercise has been shown to be an effective intervention in post-treatment care. This study aimed to gain a better understanding of breast cancer treatment-related side effects through identifying potential patient characteristic associations, including current levels of exercise. METHODS: Four hundred and thirty-two breast cancer patients completed an online survey covering their treatment and demographic background, current exercise levels, and self-reported treatment side effects. Side effects were considered in a binary logistic regression against age, surgery, currently undergoing treatment, and exercise levels to ascertain significant relationships (p < 0.05) and associative values (Odds Ratio). RESULTS: Lumpectomy patients were less likely to report aching muscles (OR 0.61, 95 % CI 0.39-0.96), hot flushes (OR 0.60, 95 % CI 0.38-0.96), and weight gain (OR 0.59, 95 % CI 0.38-0.92) than mastectomy patients. Women currently undergoing treatment were more likely to report hot flushes (OR 3.77, 95 % CI 2.34-6.08), aching muscles (OR 1.62, 95 % CI 1.02-2.57), and weight gain (OR 1.89, 95 % CI 1.19-2.99) than women finished treatment. Sedentary women were more likely to experience shoulder limitations (OR 1.77, 95 % CI 1.14-2.77), muscular chest wall pain (OR 1.69, 95 % CI 1.07-2.65), weight gain (OR 2.29, 95 % CI 1.44-3.64), lymphedema (OR 1.68, 95 % CI 1.04-2.71), and breathlessness (OR 2.30 95 % CI 1.35-3.92) than their physically active counterparts. CONCLUSIONS: Patient characteristics may inform interventions to improve care post-breast cancer treatment. Sufficient levels of exercise were consistently associated fewer side effects and should be encouraged.

Insufficient hamstring strength compromises landing technique in adolescent girls.

PURPOSE: Women sustain more anterior cruciate ligament (ACL) ruptures than men, and this gender disparity is apparent from pubertal onset. Although the hamstring muscles play a vital role in ACL protection during landing by restraining anterior tibial motion relative to the femur, it is unknown whether hamstring strength affects landing biomechanics during a functional movement. This study aimed to determine whether pubescent girls with lower hamstring strength displayed different lower limb biomechanics when landing from a leap compared with girls with higher hamstring strength. METHODS: Thirty-three healthy girls, age 10-13 yr, in Tanner stage II (pubertal onset) and 4-6 months from their peak height velocity were recruited. The concentric and the eccentric isokinetic strength of the hamstring and quadriceps muscles were assessed. On the basis of peak concentric hamstrings torque, participants were divided into a lower (peak torque < 45 N·m) and higher (peak torque > 60 N·m) strength group. Participants performed a functional landing movement, during which ground reaction forces (1000 Hz), lower limb electromyography (1000 Hz), and kinematic data (100 Hz) were collected. RESULTS: Girls with lower hamstring strength displayed significantly (P < 0.05) greater knee abduction alignment, reduced hip abduction moments, and greater ACL loading at the time of the peak anteroposterior ground reaction forces compared with their stronger counterparts. CONCLUSIONS: Girls with reduced hamstring strength appear to have a decreased capacity to control lower limb frontal plane alignment. This reduced capacity appears to contribute to increased ACL loading and, in turn, increased potential for injury.

Musculoskeletal and estrogen changes during the adolescent growth spurt in girls.

INTRODUCTION: The adolescent growth spurt is associated with rapid growth and hormonal changes, thought to contribute to the increased anterior cruciate ligament injury risk in girls. However, relatively little is known about these musculoskeletal and estrogen changes during the growth spurt in girls. PURPOSE: To investigate the longitudinal changes in estrogen as well as anterior knee laxity and lower limb strength and flexibility throughout the adolescent growth spurt in girls. METHODS: Thirty-three healthy girls, age 10-13 yr, in Tanner stage II and 4-6 months from their peak height velocity were recruited. Participants were tested up to four times during the 12 months of their growth spurt, according to the timing of their maturity offset (test 1: maturity offset = -6 to -4 months; test 2: maturity offset = 0 months; test 3: maturity offset = +4 months; test 4: maturity offset = +8 months). During each testing session, anterior knee laxity, lower limb flexibility, and isokinetic strength as well as saliva measures of estradiol concentration were measured. RESULTS: A significant (P = 0.002) effect of time on anterior knee laxity was found from the time of peak height velocity, although no changes in estradiol concentration were displayed over time (P = 0.811). Participants displayed a significant increase (P < 0.05) in isokinetic quadriceps strength over time, with no apparent increase in isokinetic hamstring strength. CONCLUSIONS: We speculate that increased quadriceps strength, combined with increased knee laxity and no accompanying hamstring strength development during the adolescent growth spurt in girls, might contribute to a decrease in their knee joint stability during landing tasks. These musculoskeletal changes could potentially increase anterior cruciate ligament injury risk at a time of rapid height and lower limb growth.

Predicting the patellar tendon force generated when landing from a jump.

PURPOSE: Although high patellar tendon loading is believed to be the primary causative factor for patellar tendinopathy, research investigating factors that affect patellar tendon loading during landing is scarce. Therefore, the purpose of this study was to identify whether factors previously associated with the development of patellar tendinopathy, and selected variables characterizing landing technique, could predict patellar tendon loading incurred by volleyball players when landing from a jump. METHODS: Ten highly skilled male, 20 skilled male, and 20 skilled female volleyball players performed a lateral stop-jump movement. Sex, skill level, quadriceps strength, quadriceps extensibility, and trunk moment of inertia were recorded. Landing kinematics (250 Hz) and kinetics (1500 Hz) were collected, and peak patellar tendon force and patellar tendon force loading rate were calculated. Backward multiple regression analyses identified which risk factors or landing technique variables were predictors of patellar tendon loading. RESULTS: Multiple regression analyses were able to estimate and predict 52% (F4,49 = 14.258, P < 0.001) and 70% (F4,49 = 29.329, P < 0.001) of the peak patellar tendon force and the patellar tendon force loading rate variance, respectively. The present study revealed that male volleyball players with greater quadriceps strength, who displayed increased ankle dorsiflexion velocity and trunk flexion velocity during landing, were predicted to incur higher patellar tendon loading. CONCLUSIONS: As frequent application of high patellar tendon loading has previously been identified as a causative factor for developing patellar tendinopathy, interventions designed to decrease ankle dorsiflexion velocity and trunk flexion velocity at landing, particularly in male players with strong quadriceps muscles, may be effective in reducing patellar tendon loading and, in turn, patellar tendinopathy prevalence in this population.

Why do girls sustain more anterior cruciate ligament injuries than boys?: a review of the changes in estrogen and musculoskeletal structure and function during puberty.

Sport is the leading cause of injury among adolescents and girls incur more non-contact anterior cruciate ligament (ACL) ruptures than boys, with this gender disparity in injury incidence apparent from the onset of puberty. Although the mechanisms for this gender disparity in ACL injuries are relatively unknown, hormonal, anatomical and biomechanical factors have been implicated. Puberty is associated with rapid skeletal growth and hormonal influx, both of which are thought to contribute to alterations in ACL metabolic and mechanical properties, as well as changes in lower limb strength and flexibility, ultimately influencing landing technique. Therefore, the aim of this review is to explain (i) the effects of changes in estrogen levels on the metabolic and mechanical properties of the ACL; (ii) changes in musculoskeletal structure and function that occur during puberty, including changes in knee laxity, and lower limb flexibility and strength; and (iii) how these hormonal and musculoskeletal changes impact upon the landing technique displayed by pubescent girls. Despite evidence confirming estrogen receptors on the ACL, there are still conflicting results as to how estrogen affects the mechanical properties of the ACL, particularly during puberty. However, during this time of rapid growth and hormonal influx, unlike their male counterparts, girls do not display an accelerated muscle strength spurt and the development of their hamstring muscle strength appears to lag behind that of their quadriceps. Throughout puberty, girls also display an increase in knee valgus when landing, which is not evident in boys. Therefore, it is plausible that this lack of a defined strength spurt, particularly of the hamstring muscles, combined with the hormonal effects of estrogen in girls, may contribute to a more 'risky' lower limb alignment during landing, in turn, contributing to a greater risk of ACL injury. There is, however, a paucity of longitudinal studies specifically examining the lower limb musculoskeletal structural and functional changes experienced by girls throughout puberty, as well as how these changes are related to estrogen fluctuations characteristic of puberty and their effects on landing biomechanics. Therefore, further research is recommended to provide greater insight as to why pubescent girls are at an increased risk of non-contact ACL injuries during sport compared with boys. Such information will allow the development of evidence-based training programmes aimed at teaching girls to land more safely and with greater control of their lower limbs in an attempt to reduce the incidence of ACL ruptures during puberty.

Effects of prolonged load carriage on ground reaction forces, lower limb kinematics and spatio-temporal parameters in female recreational hikers.

The effect of load carriage on female recreational hikers has received little attention. This study collected lower limb sagittal plane kinematic, spatio-temporal and ground reaction force (GRF) data from 15 female hikers carrying four loads (0%, 20%, 30% and 40% body weight (BW)) over 8 km. Increasing load resulted in a proportional increase in GRF up to 30% BW, increased stance time, and greater mediolateral impulse with 30% and 40% BW. Also seen were decreased velocity and cadence and increased double support and knee flexion when carrying load compared to no load. Increased distance resulted in increased knee flexion and ankle plantar flexion at initial foot-ground contact. It was concluded that, as load mass and distance increased, female hikers modified their gait to attenuate the lower limb impact forces. When carrying 30% and 40% BW loads, however, the changes aimed at attenuating the higher GRF may result in a less stable gait. PRACTITIONER SUMMARY: Limited research has investigated the biomechanical responses of female recreational hikers to prolonged load carriage. This study provides a better understanding of the effects of increasing load on lower limb kinematics, spatio-temporal parameters and the GRF generated by female hikers during prolonged load carriage. The results have implications for the development of load carriage guidelines to minimise the risk of injury to females who carry backpacks and to improve performance for this population.

Whole body kinematics and knee moments that occur during an overhead catch and landing task in sport.

BACKGROUND: Athletes suffering an anterior cruciate ligament injury tend to exhibit similar body postures that in sidestep cutting are associated with increased knee moments. This relationship, however, has not been investigated in landing. Catching a ball in different overhead positions may affect landing postures and knee joint moments. This study investigated these possible relationships. It was anticipated that some joint postures would be associated increased knee loads during the landing task. METHODS: Twenty-five healthy male team sports athletes performed four variations of a landing task. Full body kinematics were identified at initial contact. Peak flexion, valgus and internal rotation moments at the knee, measured during early landing, were normalized to mass and height and statistically compared. Intra-participant correlations were performed between all kinematics and each moment. Mean slopes for each correlation were used to identify the existence of relationships between full body kinematics and knee joint moments. Findings Landing after an overhead catch when the ball moved towards a player's support leg resulted in increased peak valgus moments. These increased valgus moments were correlated with increased knee flexion, hip flexion, and torso lean, as well as torso rotation towards the support leg, and foot and knee external rotation. Increased internal rotation moments were correlated with reduced hip abduction and external rotation, increased ankle inversion, knee external rotation and torso lean away from the support leg. Interpretation Learning to land with techniques that do not reflect postures associated with high knee moments may reduce an athlete's risk of non-contact anterior cruciate ligament injury.