Reliability and Minimal Detectable Change Values for Predictions of Knee Forces during Gait and Stair Ascent Derived from the FreeBody Musculoskeletal Model of the Lower Limb

FreeBody is a musculoskeletal model of the lower limb used to calculate predictions of muscle and joint contact forces. The validation of FreeBody has been described in a number of publications however its reliability has yet to be established. The purpose of this study was therefore to establish the test-retest reliability of FreeBody in a population of healthy adults in order to add support to previous and future research using FreeBody that demonstrates differences between cohorts after an intervention. We hypothesized that test-retest estimations of knee contact forces from FreeBody would demonstrate a high intra-class correlation. Kinematic and kinetic data from nine older participants (4 men: mean age = 63±11 years; 5 women: mean age = 49±4 years) performing level walking and stair ascent was collected on consecutive days and then analysed using FreeBody. There was a good level of intra-session agreement between the waveforms for the individual trials of each activity during testing session 1 (R = 0.79-0.97). Similarly, overall there was a good inter-session agreement within subjects (R = 0.69-0.97) although some subjects showed better agreement than others. There was a high level of agreement between the group mean waveforms of the two sessions for all variables (R = 0.882-0.997). The intra-class correlation coefficients (ICC) were very high for peak tibiofemoral joint contact forces (TFJ) and hamstring forces during gait, for peak patellofemoral joint contact forces and quadriceps forces during stair ascent and for peak lateral TFJ and the proportion of TFJ accounted for by the medial compartment during both tasks (ICC = 0.86-0.96). Minimal detectable change (MDC) of the peak knee forces during gait ranged between 0.43 and 1.53 × body weight (18-170% of the mean peak values). The smallest MDCs were found for medial TFJ share (4.1 % and 5.8% for walking and stair ascent respectively, or 4.8% and 6.7% of the mean peak values). In conclusion, the results of this study support the use of FreeBody to investigate the effect of interventions on muscle and joint contact forces at the cohort level, but care should be taken if using FreeBody at the subject level

Effect of a gluteal activation warm-up on explosive exercise performance

Objectives To evaluate the effect of a gluteal activation warm-up on the performance of an explosive exercise (the high hang pull (HHP)). Methods Seventeen professional rugby union players performed one set of three HHPs (with 80% of their one repetition maximum load) following both a control and activation warm-up. Peak electrical activity of the gluteus maximus and medius was quantified using electromyography (EMG). In addition, the kinematics and kinetics of nine players was also recorded using force plate and motion capture technology. These data were analysed using a previously described musculoskeletal model of the right lower limb in order to provide estimates of the muscular force expressed during the movement. Results The mean peak EMG activity of the gluteus maximus was significantly lower following the activation warm-up as compared with the control (p<0.05, effect size d=0.30). There were no significant differences in the mean peak estimated forces in gluteus maximus and medius, the quadriceps or hamstrings (p=0.053), although there was a trend towards increased force in gluteus maximus and hamstrings following the activation warm-up. There were no differences between the ground reaction forces following the two warm-ups. Conclusion This study suggests that a gluteal activation warm-up may facilitate recruitment of the gluteal musculature by potentiating the glutes in such a way that a smaller neural drive evokes the same or greater force production during movement. This could in turn potentially improve movement quality

Advertising paid and unpaid job roles in sport: an updated position statement from the UK Strength and Conditioning Association

Editoria

A Patient-Specific Foot Model for the Estimate of Ankle Joint Forces in Patients with Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is the leading cause of childhood disability from a musculoskeletal disorder. It generally affects large joints such as the knee and the ankle, often causing structural damage. Different factors contribute to the damage onset, including altered joint loading and other mechanical factors, associated with pain and inflammation. The prediction of patients' joint loading can hence be a valuable tool in understanding the disease mechanisms involved in structural damage progression. A number of lower-limb musculoskeletal models have been proposed to analyse the hip and knee joints, but juvenile models of the foot are still lacking. This paper presents a modelling pipeline that allows the creation of juvenile patient-specific models starting from lower limb kinematics and foot and ankle MRI data. This pipeline has been applied to data from three children with JIA and the importance of patient-specific parameters and modelling assumptions has been tested in a sensitivity analysis focused on the variation of the joint reaction forces. This analysis highlighted the criticality of patient-specific definition of the ankle joint axes and location of the Achilles tendon insertions. Patient-specific detection of the Tibialis Anterior, Tibialis Posterior, and Peroneus Longus origins and insertions were also shown to be important

In Vivo Knee Contact Force Prediction Using Patient-Specific Musculoskeletal Geometry in a Segment-Based Computational Model.

Segment-based musculoskeletal models allow the prediction of muscle, ligament and joint forces without making assumptions regarding joint degrees of freedom. The dataset published for the "Grand Challenge Competition to Predict In Vivo Knee Loads" provides directly-measured tibiofemoral contact forces for activities of daily living. For the "Sixth Grand Challenge Competition to Predict In Vivo Knee Loads", blinded results for "smooth" and "bouncy" gait trials were predicted using a customised patient-specific musculoskeletal model. For an unblinded comparison the following modifications were made to improve the predictions: • further customisations, including modifications to the knee centre of rotation; • reductions to the maximum allowable muscle forces to represent known loss of strength in knee arthroplasty patients; and • a kinematic constraint to the hip joint to address the sensitivity of the segment-based approach to motion tracking artefact. For validation, the improved model was applied to normal gait, squat and sit-to-stand for three subjects. Comparisons of the predictions with measured contact forces showed that segment-based musculoskeletal models using patient-specific input data can estimate tibiofemoral contact forces with root mean square errors (RMSEs) of 0.48-0.65 times body weight (BW) for normal gait trials. Tibiofemoral contact force patterns were estimated with an average coefficient of determination of 0.81 and with RMSEs of 0.46-1.01 times BW for squatting and 0.70-0.99 times BW for sit-to-stand tasks. This is comparable to the best validations in the literature using alternative models

Repeated horizontal jumping is a feasible exercise countermeasure for microgravity

Objectives: Astronauts who spend prolonged time in microgravity on the International Space Station can experience a significant reduction in physical fitness. Jumping exercises represent a potential solution to this problem as the European Space Agency has demonstrated that the deconditioning effect of long-term bed-rest can be countered with around four minutes per day of jumping. The purpose of this study was to evaluate if repeated jumping is possible in microgravity and if the transmission of impact forces and vibration to the aircraft can be minimised. Methods: Five subjects performed repeated jumping on a custom jump sled both in microgravity during a parabolic flight campaign and in normal gravitational conditions. Forces expressed by the user and transmitted to the aircraft were quantified using a bespoke instrumentation system. Results: These results show, for the first time, that repeated horizontal jumping is possible in microgravity, and that force transmission can be minimised by using a custom supine jump sled. The peak effective ground reaction force experienced by the user was sensitive to both the style of jumping used and resistance employed. Conclusion: These results open the door to the next generation of exercise countermeasures for deep space exploration. In particular, we have qualified the High Frequency Impulse for Microgravity (HIFIm) exercise device to a Technology Readiness Level of 6 making it a leading candidate to replace the Advanced Resistive Exercise Device (ARED) which has been in service since 2009

Landing Style Influences Peak ‘Ground’ Reaction Forces during Repeated Jumping Using a Supine Jump Sled in Microgravity

Repeated jumping has been demonstrated as a feasible exercise countermeasure in microgravity and has been shown to reduce deconditioning in head down bed rest studies. However, varying landing stiffness may provide greater contribution of both axial and medio-lateral bone strain and muscle loading at greater muscle lengths, which may help minimize bone and muscle deconditioning. Therefore, this study investigated the effect of different landing styles on the force profile and ground contact time during repeated jumping using HIFIm in microgravity. Two participants performed repeated jumping on the HIFIm jump sled in microgravity during a parabolic flight campaign. ‘Ground’ forces and ground contact time were compared between landing styles where increased landing stiffness was instructed to the jumper, and increased spring resistance. The results show that the forces experienced when performing repeated jumps in microgravity are sensitive to the landing style employed. As greater stiffness was instructed, peak forces increased, and ground contact time decreased significantly. Peak forces and ground contact time also significantly increased when spring resistance increased. These results highlight that landing instructions and spring configurations could be used as training variables when developing an astronaut training program, which can use different jump styles to minimize bone and muscle deconditioning. Further research using bed rest analogs and repeated jumping using HIFIm is needed to demonstrate varied repeated jumping interventions as an effective exercise method for minimizing deconditioning in astronauts

Jumping demands during classical ballet class.

Ballet class represents a considerable portion of professional ballet training, yet the external training load demands associated with class-and particularly the jumping demands-have not been investigated. The purpose of this study was to measure the jumping demands of ballet class by sex and rank. Eleven female and eight male elite professional ballet dancers participated in 109 ballet classes taught by 12 different teachers. Jump counts and jump heights were measured during each class. A Poisson generalized linear mixed effects model was used to examine the differences in jump counts between sexes and ranks. Greater jump counts were observed during class in men than in women (153, 95% confidence intervals [CI] [137, 170] vs. 119, 95% CI [109, 131], p = 0.004) and in junior ranking dancers compared with senior ranking dancers (151, 95% CI [138, 165] vs. 121, 95% CI [108, 135], p = 0.006). Female junior and senior ranking dancers jumped at rates of 9.2 ± 2.6 and 8.6 ± 4.7 jumps·min , respectively, while male junior and senior ranking dancers jumped at rates of 9.1 ± 2.6 and 8.7 ± 2.6 jumps·min , respectively. Across all classes, 73% of jumps observed were below 50% of maximum double-legged countermovement jump height. Unlike rehearsals and performances, class offers dancers an opportunity to self-regulate load, and as such, are a useful session to manage jump load, and facilitate gradual return-to-dance pathways. Communication between health care and artistic staff is essential to facilitate load management during class