Using passive or active back-support exoskeletons during a repetitive lifting task: influence on cardiorespiratory parameters.

The objective of this laboratory study was to assess the cardiorespiratory consequences related to the use of different back-support exoskeletons during a repetitive lifting task. Fourteen women and thirteen men performed a dynamic stoop lifting task involving full flexion/extension of the trunk in the sagittal plane. This task was repeated for 5 min with a 10 kg load to handle. Four conditions were tested: with a passive exoskeleton (P-EXO), with two active exoskeletons (A-EXO1 and A-EXO2), as well as without exoskeleton (FREE). The oxygen consumption rate and cardiac costs were measured continuously. Results showed a significantly lower (p < 0.05) oxygen consumption rate for all exoskeletons as compared to FREE (12.6 ± 2.2 ml/kg/min). The values were also significantly lower (p < 0.001) for A-EXO1 (9.1 ± 1.8 ml/kg/min) compared to A-EXO2 (11.0 ± 1.8 ml/kg/min) and P-EXO (11.8 ± 2.4 ml/kg/min). Compared to FREE (59.7 ± 12.9 bpm), the cardiac cost was significantly reduced (p < 0.001) only for A-EXO1 (45.1 ± 11.5 bpm). Several factors can explain these differences on the cardiorespiratory parameters observed between exoskeletons: the technology used (passive vs active), the torque provided by the assistive device, the weight of the system, but also the level of anthropomorphism (related to the number of joints used by the exoskeleton). Our results also highlighted the lack of interaction between the exoskeleton and sex. Thereby, the three back-support exoskeletons tested appeared to reduce the overall physical workload associated with a repetitive lifting task both for men and women.

Effects of perturbation or plyometric training on core control and knee joint loading in women during lateral movements.

Deficits in trunk control are argued to increase the risk of knee injuries. However, no existing training program effectively addresses trunk control during lateral movements, such as cutting maneuvers. The purpose of this study was to investigate whether a combination of perturbation and plyometric training (PPT) would reduce trunk excursions against the new movement direction and reduce knee joint moments during lateral movements. Twenty-four active women participated in a RCT, where trunk and pelvis kinematics and knee joint moments were measured during lateral reactive jumps (LRJ) and unanticipated cutting maneuvers before and after a 4-week PPT program and compared to a control group. During LRJ, trunk rotation away from the new movement direction was reduced (P < 0.001), while pelvis rotation toward the new direction was increased (P = 0.006) after PPT. Moreover, decreased knee extension moments (P = 0.028) and knee internal rotation moments (P < 0.001) were reported after both trainings. Additionally, PPT reduced trunk rotation by 7.2° during unanticipated cuttings. A 4-week PPT improved core control by reducing trunk rotation and reduced knee joint moments during LRJ. During training, perturbations should be introduced to improve core control during dynamic athletic movements, possibly reducing the risk of ACL injuries.

Influence of Gender on Trunk and Lower Limb Biomechanics during Lateral Movements.

This study investigates gender differences in lateral trunk lean to confound possible associations with hip and knee joint biomechanics during lateral reactive jumps. Twelve female and 12 male athletes performed lateral reactive jumps while three-dimensional knee, hip and trunk kinematics as well as ground reaction forces and electromyography of selected thigh muscles were recorded. Lateral trunk lean did not differ between genders, while females had greater knee valgus angle than males (-4.9 ± 3.9° vs. 1.6 ± 3.2°, p = 0.001). A significant association between the lateral trunk lean and the hip abduction moment (r = 0.55) was found. Moreover, lateral trunk lean and knee abduction moment showed a significant relationship (r = 0.67). The positive association between trunk lean and knee abduction moment suggests that higher lateral trunk lean may increase the risk of knee injury during lateral movements and that the trunk should be trained accordingly in team sports.

Knee and hip joint biomechanics are gender-specific in runners with high running mileage.

Female runners are reported to be more prone to develop specific knee joint injuries than males. It has been suggested that increased frontal plane joint loading might be related to the incidence of these knee injuries in running. The purpose of this study was to evaluate if frontal plane knee and hip joint kinematics and kinetics are gender-specific in runners with high mileage. 3D-kinematics and kinetics were recorded from 16 female and 16 male runners at a speed of 3 m/s, 4 m/s, and 5 m/s. Frontal plane joint angles and joint moments were ascertained and compared between genders among speed conditions. Across all speed conditions, females showed increased hip adduction and reduced knee adduction angles compared to males (p < 0.003). The initial peak in the hip adduction moment was enhanced in females (p = 0.003). Additionally, the hip adduction impulse showed a trend towards an increase in females at slow running speed (p = 0.07). Hip and knee frontal plane joint kinematics are gender-specific. In addition, there are indications that frontal plane joint loading is increased in female runners. Future research should focus on the relationship of these observations regarding overuse running injuries.

How to sprain your ankle - a biomechanical case report of an inversion trauma.

In order to develop preventive measures against lateral ankle sprains, it is essential to have a detailed understanding of the injury mechanism. Under laboratory experimental conditions the examination of the joint load has to be restricted with clear margins of safety. However, in the present case one athlete sprained his ankle while performing a run-and-cut movement during a biomechanical research experiment. 3D kinematics, kinetics, and muscle activity of the lower limb were recorded and compared to 16 previously performed trials. Motion patterns of global pelvis orientation, hip flexion, and knee flexion in the sprain trail deviated from the reference trials already early in the preparatory phase before ground contact. During ground contact, the ankle was rapidly plantar flexed (up to 1240°/s), inverted (up to 1290°/s) and internally rotated (up to 580°/s) reaching its maximum displacement within the first 150 ms after heel strike. Rapid neuromuscular activation bursts of the m. tibialis anterior and the m. peroneus longus started 40-45 ms after ground contact and overshot the activation profile of the reference trials with peak activation at 62 ms and 74 ms respectively. Therefore, it may be suggested that neuromuscular reflexes played an important role in joint control during the critical phase of excessive ankle displacement. The results of this case report clearly indicate that (a) upper leg mechanics, (b) pre-landing adjustments, and (c) neuromuscular contribution have to be considered in the mechanism of lateral ankle sprains.

Muscle coordination while pulling up during cycling.

The aim of this study was to determine the influence of the pull up action on the pedalling mechanics and muscle coordination during cycling. 9 elite cyclists pedalled at 320 watts with their preferred technique and while pulling up. The pull up action increased significantly the pedalling effectiveness during the upstroke and around the bottom dead centre. This was associated with a significant enhancement of the biceps femoris activity (48%), an earlier onset of activation of the tibialis anterior, i. e., 211 ± 83° vs. 259 ± 22° (crank angle) and a delayed offset of activation of the gastrocnemius lateralis, i. e., 244 ± 19° vs. 216 ± 39°. Consequently, co-activities between tibialis anterior and gastrocnemius lateralis muscles over 55 ± 65° (crank angle range), as well as between the biceps femoris and the tibialis anterior over 48 ± 57° were generated. These higher co-activities were necessary to stiffen the ankle joint and to power the pedal during the upstroke. Thus changes in muscle coordination improved the pedalling effectiveness during the upstroke phase but would probably lead to impairment of the oxygen consumption. Therefore, training the pull up action could be of interest to optimize this muscle coordination associated with better pedalling effectiveness by additionally relieving hip or knee extensors during the downstroke.

Effects of pedal type and pull-up action during cycling.

The aim of this study was to determine the influence of different shoe-pedal interfaces and of an active pulling-up action during the upstroke phase on the pedalling technique. Eight elite cyclists (C) and seven non-cyclists (NC) performed three different bouts at 90 rev . min (-1) and 60 % of their maximal aerobic power. They pedalled with single pedals (PED), with clipless pedals (CLIP) and with a pedal force feedback (CLIPFBACK) where subjects were asked to pull up on the pedal during the upstroke. There was no significant difference for pedalling effectiveness, net mechanical efficiency (NE) and muscular activity between PED and CLIP. When compared to CLIP, CLIPFBACK resulted in a significant increase in pedalling effectiveness during upstroke (86 % for C and 57 % NC, respectively), as well as higher biceps femoris and tibialis anterior muscle activity (p < 0.001). However, NE was significantly reduced (p < 0.008) with 9 % and 3.3 % reduction for C and NC, respectively. Consequently, shoe-pedal interface (PED vs. CLIP) did not significantly influence cycling technique during submaximal exercise. However, an active pulling-up action on the pedal during upstroke increased the pedalling effectiveness, while reducing net mechanical efficiency.

Barefoot-shod running differences: shoe or mass effect?

The higher oxygen consumption reported when shod running is compared to barefoot running has been attributed to the additional mass of the shoe. However, it has been reported that wearing shoes also modified the running pattern. The aim of this study was to distinguish the mass and shoe effects on the mechanics and energetics when shod running. Twelve trained subjects ran on a 3-D treadmill ergometer at 3.61 m . s (-1) in six conditions: barefoot, using ultra thin diving socks unloaded, loaded with 150 g, loaded with 350 g, and two shoe conditions, one weighing 150 g and another 350 g. The results show that there was a significant mass effect but no shoe effect for oxygen consumption. Stride frequency, anterior-posterior impulse, vertical stiffness, leg stiffness, and mechanical work were significantly higher in barefoot condition compared to shod. Net efficiency, which has metabolic and mechanical components, decreased in the shod condition. The mechanical modifications of running showed that the main role of the shoe was to attenuate the foot-ground impact by adding damping material. However, these changes may lead to a decrease of the storage and restitution of elastic energy capacity which could explain the lower net efficiency reported in shod running.

Development and evaluation of a new bicycle instrument for measurements of pedal forces and power output in cycling.

Determination of pedal forces is a prerequisite to analyse cycling performance capability from a biomechanical point of view. Comparing existing pedal force measurement systems, there are methodological or practical limitations regarding the requirements of scientific sports performance research and enhancement. Therefore, the aim of this study was to develop and to validate a new bicycle instrument that enables pedal forces as well as power output measurements with a free choice of pedal system. The instrument (Powertec-System) is based on force transducer devices, using the Hall-Effect and being mounted between the crank and the pedal. Validation of the method was evaluated by determining the accuracy, the cross talk effect, the influence of lateral forces, the reproducibility and, finally, a possible drift under static conditions. Dynamic tests were conducted to validate the power output measurement in reference to the SRM-System. The mean error of the present system was -0.87 +/- 4.09 % and -1.86 +/- 6.61 % for, respectively, the tangential and radial direction. Cross talk, lateral force influence, reproducibility and drift mean values were < +/- 7 %, < or = 2.4 %, < 0.8 % and 0.02 N x min (-1), respectively. In dynamic conditions, the power output measurement error could be kept below 2.35 %. In conclusion, this method offers the possibility for both valid pedal forces and power output measurements. Moreover, the instrument allows measurements with every pedal system. This method has an interesting potential for biomechanical analyses in cycling research and performance enhancement.

Mechanical comparison of barefoot and shod running.

In order to further compare shod versus barefoot running, 35 subjects ran two bouts of 4 minutes at 3.33 m x s(-1) on a treadmill dynamometer. Parameters were measured on about 60 consecutive steps. Barefoot showed mainly lower contact and flight time (p < 0.05), lower passive peak (1.48 versus 1.70 body weight, p < 0.05), higher braking and pushing impulses (p < 0.05), and higher pre-activation of triceps surae muscles (p < 0.05) than shod. It was concluded that when performed on a sufficient number of steps, barefoot running leads to a reduction of impact peak in order to reduce the high mechanical stress occurring during repetitive steps. This neural-mechanical adaptation could also enhance the storage and restitution of elastic energy at ankle extensors level.