Differences in support leg kinetics between non-sprinters and sprinters during maximal speed sprinting

Running mechanics could be influenced by some degenerative musculoskeletal changes associated with ageing. However, the shoe effect on ground reaction force (GRF) amplitude and complexity of older runners is still unclear. The objective of our study was to assess the effects of age and shoe on amplitude and complexity of GRF during treadmill running. In total, 20 healthy runners were recruited. GRF data were collected for 13 younger runners and seven older runners during running on an instrumented treadmill at 3.5 m/s. Maximum vertical loading rate and GRF variables were generated. Sample entropy of GRF during the first 20% of the stance phase was calculated to assess GRF complexity. Age and shoe type did not significantly affect the maximal loading rate and GRF. Older participants exhibited higher anteroposterior and vertical GRF sample entropy compared to younger runners. In conclusion, the amplitudes of GRF were not influenced by age group, which indicated that muscle strength in the older runners tested could fulfil mechanical demand (e.g., shock absorption, force generation) during running. However, the increased GRF complexity in initial stance phase with ageing could be a result of reduced muscle contraction coordination and smoothness of force production.

It has been shown that short-leg walking boots alter kinematics, joint kinetics and ground reaction forces (GRFs) during gait. The altered GRF variables may be associated with the increased heel height on the walker side compared to the shoe side. By modifying the walking boots, it was hypothesized that the diminished heel height difference between the walker side and the shoe side would restore GRF characteristics closer to those in normal walking. PURPOSE: To examine effects of heel height modifications on the walker and shoe sides on GRF characteristics during level walking. METHODS: Ten (four males, six females) subjects performed five level walking trials in each of six randomized conditions: lab shoes (Shoe), Gait walker (GW), Gait Walker with heel insert (GWHI), Gait walker modified (GWM), Equalizer walker (EW), and Equalizer walker with heel insert (EWHI). A force platform (1200 Hz) and a seven-camera motion analysis system (120 Hz) were used to collect GRF during the testing session. Visual 3D and customized computer software were used to obtain GRF data. A two-way (2 × 6: side × condition) mixed design ANOVA was used to examine selected peak GRF related variables and post hoc comparisons with an alpha level (p < 0.05) adjusted for multiple comparisons through a Bonferroni procedure. RESULTS: The application of a walker created a peak GRF prior to the normal peaks associated with the loading response in both vertical and anteroposterior GRFs. Wearing a walker introduced an elevated minimum vertical GRF in GW (0.88 BW), GWHI (0.89 BW), GWM (0.89 BW) and EWHI (0.88 BW) compared to Shoe (0.82 BW) on the shoe (left) side. Peak propulsive GRFs were smaller in all five walker conditions (0.13 - 0.15 BW) compared to Shoe (0.20 BW) on the walker side. The same peak was smaller in GWHI, EW and EWHI on the walker side compared to the shoe side whereas it was greater on the right side than the left side in Shoe. CONCLUSION: The application of heel insert in GWHI and GWM (on shoe side) does not diminish the minimum vertical GRF as hypothesized. Wearing a walker decreases the peak propulsive ground reaction force on the walker side and induces asymmetrical loading.

Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness during the first stance phase of the push-off. One elite sprinter performed 10 maximal sprint starts. An automatic motion analysis system (CODA, 200 Hz) with synchronized force plates (Kistler, 1000 Hz) collected kinematic profiles at the hip, knee, and ankle and ground reaction forces, providing input for inverse dynamics analyses. The lower-limb joints predominately extended and revealed a proximal-to-distal sequential pattern of maximal extensor angular velocity and positive power production. Pearson correlations revealed relationships (P < 0.05) between ankle stiffness (5.93 ± 0.75 N · m · deg−1) and selected performance variables. Relationships between negative power phase ankle stiffness and horizontal (r = −0.79) and vertical (r = 0.74) centre of mass velocities were opposite in direction to the positive power phase ankle stiffness (horizontal: r = 0.85; vertical: r = −0.54). Thus ankle stiffness may affect the goals of the sprint push-off in different ways, depending on the phase of stance considered.

Altered ground reaction force (GRF) during cutting is associated with chronic ankle instability (CAI). Little is known whether a rehabilitation intervention alters GRF patterns during a cutting task. PURPOSE: To examine the effect of a 6-week ankle and hip intervention program on GRF during the stance phase of cutting in patients with CAI. METHODS: 15 CAI subjects in a rehab group (23±2 yrs, 178±8 cm, 76±9 kg, 83±7% FAAM ADL, 56±10% FAAM Sports, 3.6±1.1 MAII, 4.7±2.0 ankle sprains) completed a series of 10 ankle and hip strength and proprioceptive exercises (theraband, wobble board, ankle disk, etc.) 3 times/week for 6 weeks under supervision. 14 CAI subjects participated in a control group (22±2 yrs, 177±9 cm, 75±12 kg, 81±9% FAAM ADL, 56±12% FAAM Sports, 3.4±1.2 MAII, 5.9±3.3 sprains). Subjects performed 10 jumps consisting of a max vertical jump plus a side cut. Functional analyses (α=.05) were used to detect a group x treatment interaction over time. If 95% CI did not cross the zero, significant differences existed. RESULTS: Figure 1. The rehab intervention resulted in up to (i) 0.16 N/kg less vertical GRF at 3-9% of stance, and 0.21 N/kg more vertical GRF at 17-23% and 39-74% of stance, (ii) 0.06 N/kg more posterior GRF at 11-22% and 38-48% of stance, and 0.03 N/kg less posterior GRF at 82-97% of stance, while no changes were detected in medial-lateral GRF. CONCLUSION: Relative to the control group, CAI patients in the rehab group tend to land with greater vertical and posterior GRF, which results in a stiffer landing. While this may lead to a faster execution of the cutting task, greater vertical GRF could result in greater impact loads in the lower extremity, which might increase the risk of ankle injury in a CAI population.Figure

Hamstring muscle strains are one of the most frequent injuries in sports. They are thought to occur during the late swing phase of gait when the hamstring is lengthening and eccentrically contracting. PURPOSE: The purpose of this study was to assess the difference in injury risks during testing at maximum and sub-maximum speeds by identifying kinematic differences at the hip and knee during the late swing phase of both speeds. METHODS: Ten athletes (21.8 ±3.5 years, 1.78 ± 0.07m, 78.11 ± 13.90kg) with no history of lower extremity injuries in the past 6 months, who could run faster than 6.83m/s were tested. Informed consent was obtained prior to testing. Kinematic data was collected using an 8 camera motion capture system sampling at 240Hz. Five maximum speed trials were conducted, after which an average speed was calculated and 90% of this speed was used for the 5 sub-maximal speed trials. Sprinting speed was monitored using two sets of infrared photocells. Subjects ran within ±5% of the indicated speed for all trials. Analysis was performed on one gait cycle for each subject's dominant limb. A series of paired t-test were used to test for significant differences between the two test speeds (α=0.05). RESULTS: Significant differences existed between maximum and sub-maximum running speeds (p<0.01). The average stance phase as a percentage of the gait cycle was 16.96% and 18.17% for maximum and sub-maximum speeds, respectively (p=0.004). The maximum hip flexion angle was significantly larger for the maximum speed (76.97o) when compared to the sub-maximum (74.25o) speed (p=0.01). The knee flexion angle at the point of maximum hip flexion were 78.98° and 75.98° for the maximum and sub-maximum sprinting speeds, respectively (p=0.02). Therefore, the knee was more extended during the sub-maximum sprinting speed. The average stride length during sub-maximum sprinting was significantly longer than the stride length during the maximum sprinting speed (p=0.008). CONCLUSIONS: Based on the results of this study, joint kinematics are different between the maximum and sub-maximum speeds indicating the importance of completing biomechanical testing at a maximum speed when assessing the potential for hamstring injuries.

The purpose of this study was to examine the overall kinetics and the kinetics at the joints of the lower limb while sprinting at maximum speed, and to compare the data of a double transtibial amputee and able‐bodied controls running at the same level of performance. One double transtibial amputee, using dedicated sprinting prostheses, and five able‐bodied sprinters participated in the study. The athletes performed submaximal and maximal sprints (60 m) on an indoor track. All of the participants ran three times at each speed (maximal and submaximal). The athletes’ kinematics were recorded using the Vicon 624 system with 12 cameras operating at 250 Hz. Four Kistler force plates (1250 Hz) were used to record ground reaction forces (GRF). External joint moments, joint work, and joint power were calculated from the GRF and the kinematic data. The analysis of total body kinetics revealed lower mechanical work during the stance phase for the double transtibial amputee using Cheetah prostheses than for the able‐...

Rules of nature’s Formula Run: Muscle mechanics during late stance is the key to explaining maximum running speed

To provide an integrative framework of endurance performance, the anaerobic speed reserve gained increasing popularity in middle-distance running. The present study investigated athlete profiles and performance predications based on the anaerobic speed reserve framework in 400m athletes. Descriptive laboratory study. Maximal oxygen uptake, lactate threshold (vL4), maximal sprinting speed, maximal aerobic speed, and speed reserve ratio (speed reserve ratio; maximal sprinting speed:maximal aerobic speed) of national level and elite German 400m-sprinters (n = 13 females, age [yrs]: 20.8 ± 3.1, personal best (PB400) [s]: 55.1 ± 3.0 & n = 5 males, age: 22.8 ± 3.1, PB400: 46.7 ± 1.0) were assessed. A prediction model for 400m performance was computed via stepwise multiple regression. K-means clustering was calculated based on the speed reserve ratio. Maximal sprinting speed, maximal aerobic speed and vL4 showed moderate to large negative bivariate correlations with 400m performance (-0.61 < r < -0.94; p ≤ 0.008). Backward stepwise regression revealed maximal sprinting speed and maximal aerobic speed as strong predictors for 400m performance (adjusted R2 = 0.90, standard error of the estimate = 1.447 s [2.6 %]). K-means clustering revealed two distinct subgroups along the speed reserve ratio-continuum (sprint-type: speed reserve ratio ≥1.81; endurance-type: speed reserve ratio ≤1.77). Maximal sprinting speed and maximal aerobic speed are powerful predictors for 400m performance, with vL4 also being associated with 400m performance. Speed reserve ratio calculation enables a differentiation between 400m sprint-type and endurance-type athletes. The interplay of maximal sprinting speed and maximal aerobic speed enables a broader understanding of the contributing factors to 400m performance. These parameters may support coaches in programming training tailored to individual needs during different training periods.

Background &amp; Objectives: Sprint races are extremely popular in athletic competitions. Although those events have hitherto mainly been studied from a split-time perspective, at present, the nature of the adjustments in sprint mechanics and the extent to which stride parameters are altered are yet to be fully elucidated. This study was undertaken to test the hypothesis that single, maximal treadmill sprints (100 m, 200 m and 400 m) modify running kinetic-kinematic variables and spring-mass characteristics, with larger magnitude changes as sprint distance increases. Methods: Eleven physically active males performed 100-, 200- and 400-m running sprints on a validated instrumented sprint ergometer (ADAL3D-WR, Medical Development - HEF Tecmachine, Andrézieux-Bouthéon, France), which allowed subjects to run and produce speed ''freely'', i.e. with no predetermined belt speed imposed. Vertical and horizontal ground reaction forces were measured continuously (averaged every 50 m distance intervals) and used to determine stride parameters and spring-mass behavior. Results: Compared with the initial 50 m, running speed decreased (P&lt;0.001) by 8±2%, 20±4% and 39±7% at the end of the 100, 200 and 400 m, respectively. All sprint distances (with the exception of stride length in the 100 m) induced significant (P&lt;0.05) increments in contact (+7±4%, +22±8% and +36±13%) and swing times (+12±15%, +16±15% and +16±9%) and decrements in stride lengths (-1±4%, -5±5% and -41±2%) and frequencies (-6±3%, -13±7% and -22±8%) at the end of the 100, 200 and 400 m, respectively. Running kinetics all significantly decreased (P&lt;0.001): mean vertical and total ground reaction forces for each step were reduced by about 2, 7 and 17% in the 100, 200 and 400 m, while net horizontal forces decreased by 14±17%, 41±21% and 121±35% on average. On the 100 m, the only spring-mass parameters to change (P&lt;0.001) were an increased center of mass vertical displacement and a decreased vertical stiffness (+13±7% and -12±6%, respectively), with no change in leg stiffness. All the leg-spring variables significantly changed (P&lt;0.05) over the 200 and 400 m: peak vertical forces: -6±3% vs. -14±9%; center of mass vertical displacement: +36±20% vs. +48±23%; leg compression: +8±8% vs. +8±9%; vertical stiffness: -30±11% vs. -63±20%; leg stiffness: -12±8% vs. -23±18%, respectively. Multiple linear regression analysis with best subset approach showed that 96% of the variation in speed was explained by stride length (ß=1.7) and frequency (ß=4.5) during 100 m. Stride length (ß=3.7) was also important predictor for speed during 200 m along with flight (ß=-24.9) and contact (ß=-25.6) times (r2=0.98), while leg stiffness showed a negative association (ß=-0.08) for predicting speed in the 400 m sprint model together with stride length (ß=-24.8) and contact time (ß=1.9) (r2=0.92). Conclusion: Along with speed, the magnitude of changes in running kinematics-kinetics and spring-mass behavior over short (100 m), intermediate (200 m) and long (400 m) treadmill sprint increased with sprint distance. Stride length was positively associated with speed in all sprint distances. Future research should evaluate the effects of various individualized training interventions on optimizing musculo-skeletal stiffness regulation, and their effects on sprinting speed development and maintenance.

Abrupt changes in kinematics during sprint acceleration called transitions have previously been observed. This study aimed to examine whether ground reaction force (GRF) variables during sprint acceleration also show specific features of the transitions. Twenty-one male sprinters performed 60-m sprints, during which GRF data were recorded. Step-to-step spatiotemporal and GRF variables were approximated using an exponential function and three straight lines. Moreover, statistical parametric mapping (SPM) was used to test changes in GRF curves across the transitions. For running speed, the exponential approximation resulted in smaller root-mean-square (RMS) of residuals. For the other variables, however, RMS of residuals was smaller when the three lines approximation was adopted. Breakpoints around the 5th and 15th steps were detected using effective vertical impulse during the braking phase with the three lines approximation. Across the breakpoints, SPM showed significant differences in the antero-posterior GRF curves at the next step after the first breakpoint and at the second breakpoint. Moreover, the second braking phase of the antero-posterior GRF appeared at the next step after the first breakpoint, and the corresponding first propulsive phase disappeared at the second breakpoint. Consequently, changes in GRF variables during sprint acceleration are likely accompanied by specific alterations. The breakpoints around the 5th and 15th steps found in an effective vertical impulse during the braking phase can be a criterion indicating transitions in GRF variables during sprint acceleration. The transitions are characterized by an appearance and disappearance of the second braking and first propulsive phases, respectively, of the antero-posterior GRF.

An important aspect of gait analysis is the measurement and interpretation of the Ground Reaction Force (GRF) characteristics. These measurements are important for the calculation and analysis of joint moments and forces, in addition to its assistance in natural and artificial walk control. Usually, a force platform, requiring a large space, is used to obtain these measurements but only few steps could be analyzed. To carry out continuous GRF measurements for long time walking, a force platform embedded in a single-belt treadmill can be used. The difficulty of such systems arises from the fact that the resultant GRF of the two feet is obtained during double stance phase of the walk cycle. The present study proposes the use of a mathematical model to develop a method for the separation of these superimposed vertical GRF from the center of pressure (CoP) profile. Gait events were detected in order to specify the regions of double stance and to specify the GRF model during these periods. The performance of different mathematical functions in modeling the vertical GRF was examined. The results show that a model utilizing a hyperbolic tangent function (sigmoid) represents the best fit to the vertical GRF data. Our model is highly recommended for real-time monitoring of continuous GRF treadmill measurements that would facilitate and speed up the gait analysis and diagnosis done by physicians.

Measurements of multi-axial Ground Reaction Force (GRF) can provides quite useful information for monitoring abnormalities of gait during Activities in Daily Living (ADL). Measuring multi-axial GRF using ambulatory GRF sensing systems is difficult due to the height of sensor and the number of sensors used. Therefore, we developed a wireless GRF sensing system having the low height (12 mm) and the capability of sensing simultaneously lateral and vertical GRF using only four optical sensors. The proposed biaxial force sensor showed the low interference rate (less than 0.1 %) and excellent repeatability (0.6 %). We extracted the lateral and vertical GRFs via Bluetooth communication during normal and pronated/supinated walking and presented a three dimensional vector diagram employing center of pressure and GRFs to provide visualization of the ratio between the lateral and vertical GRFs according to the amount of foot pronation. In healthy subjects, the lateral forces were observed less than 10 % of their bodyweights, while large lateral forces were observed in over pronated/supinated walking up to 20 %.

This study assessed the validity of 5-m (TG5) and 10-m (TG10) split times measured with timing gates to estimate maximum sprint speed (MSS) against a criterion measure radar gun (RG) during the maximum velocity phase of a 30-m sprint. Nineteen amateur rugby players performed two 30-m sprints. The timing gates were placed at the starting line and at 5-, 10-, 20-, 25- and 30-m. In addition, a RG was used to measure instantaneous velocity. Both trials per participant were used selected as references. MSS obtained from TG10, TG5 and RG showed high intraclass correlation coefficients (0.971–0.978), low coefficients of variation (1.14–1.70%) and smallest detectable changes (<0.02 m/s). Pairwise comparison revealed differences (p = 0.002) in MSS when comparing TG10 to RG, but not TG5 and RG (p = 0.957). Almost perfect correlations were found between RG, TG5 and TG10 (r > 0.926, p < 0.001). In conclusion, MSS obtained from TG5, TG10 and RG presented good intra-session reliability. However, practitioners should be aware that substantial differences exist between TG10 and RG. For the assessment of MSS in team-sport athletes, it is recommended the use of TG5 for more accurate estimations when a gold standard criterion is not available.

ACL Research Retreat V

Establish test re-test reliability of three tests assessing hamstring function during hip extention and investigate their associations with maximal sprinting speed. Cross-sectional. Biomechanics laboratory. Twenty healthy, physically active men (age=26±5 years; height=1.81±0.07m; body mass=81±7kg). Participants performed a maximal sprinting speed test on a non-motorised-treadmill (NMT) and three tests assessing hamstring function (hamstring scooter, hamstring push and hamstring switch), during test and re-test sessions seven days apart. Hamstring scooter peak horizontal force was measured using the NMT, while hamstring push and hamstring switch peak hip extension forces were measured using force plates (ForceDecks Lite, Vald Performance, Brisbane, Australia). We calculated each test's intraclass correlation coefficient (ICC) with 95% confidence intervals (95% CI) within (ICC2,1) test and re-test sessions, respectively, and between (ICC2,k) test and re-test sessions, along with Pearson's correlation coefficient (r-value) with maximal sprinting speed. Test re-test reliability ranged from moderate to excellent for all tests. The hamstring scooter was the only test with a statistically significant association (p<0.01; r=0.76) with maximal sprinting speed. The tests described in this study all had moderate to excellent test re-test reliability, but only the hamstring scooter was associated with maximal sprinting speed.