Niels Jensby Nedergaard

Training Load Monitoring in Team Sports: A Novel Framework Separating Physiological and Biomechanical Load-Adaptation Pathways

There have been considerable advances in monitoring training load in running-based team sports in recent years. Novel technologies nowadays offer ample opportunities to continuously monitor the activities of a player. These activities lead to internal biochemical stresses on the various physiological subsystems; however, they also cause internal mechanical stresses on the various musculoskeletal tissues. Based on the amount and periodization of these stresses, the subsystems and tissues adapt. Therefore, by monitoring external loads, one hopes to estimate internal loads to predict adaptation, through understanding the load-adaptation pathways. We propose a new theoretical framework in which physiological and biomechanical load-adaptation pathways are considered separately, shedding new light on some of the previously published evidence. We hope that it can help the various practitioners in this field (trainers, coaches, medical staff, sport scientists) to align their thoughts when considering the value of monitoring load, and that it can help researchers design experiments that can better rationalize training-load monitoring for improving performance while preventing injury.

The Relationship Between Whole-Body External Loading and Body-Worn Accelerometry During Team Sports Movements.

PURPOSE To investigate the relationship between whole-body accelerations and body-worn accelerometry during team-sport movements. METHODS Twenty male team-sport players performed forward running and anticipated 45° and 90° side-cuts at approach speeds of 2, 3, 4, and 5 m/s. Whole-body center-of-mass (CoM) accelerations were determined from ground-reaction forces collected from 1 foot-ground contact, and segmental accelerations were measured from a commercial GPS accelerometer unit on the upper trunk. Three higher-specification accelerometers were also positioned on the GPS unit, the dorsal aspect of the pelvis, and the shaft of the tibia. Associations between mechanical load variables (peak acceleration, loading rate, and impulse) calculated from both CoM accelerations and segmental accelerations were explored using regression analysis. In addition, 1-dimensional statistical parametric mapping (SPM) was used to explore the relationships between peak segmental accelerations and CoM-acceleration profiles during the whole foot-ground contact. RESULTS A weak relationship was observed for the investigated mechanical load variables regardless of accelerometer location and task (R2 values across accelerometer locations and tasks: peak acceleration .08-.55, loading rate .27-.59, and impulse .02-.59). Segmental accelerations generally overestimated whole-body mechanical load. SPM analysis showed that peak segmental accelerations were mostly related to CoM accelerations during the first 40-50% of contact phase. CONCLUSIONS While body-worn accelerometry correlates to whole-body loading in team-sport movements and can reveal useful estimates concerning loading, these correlations are not strong. Body-worn accelerometry should therefore be used with caution to monitor whole-body mechanical loading in the field.

Using accelerometry to quantify deceleration during a high-intensity soccer turning manoeuvre

Abstract The mechanics of cutting movements have been investigated extensively, but few studies have considered the rapid deceleration phase prior to turning which has been linked to muscle damage. This study used accelerometry to examine the influence of turning intensity on the last three steps of a severe turn. Ten soccer players performed 135° “V” cuts at five different intensities. Resultant decelerations were recorded from a trunk-mounted tri-axial accelerometer. Lower limb kinematics and ground reaction forces (GRF) from the pivot foot-ground contact (FGC) were also monitored. Average peak trunk decelerations were larger at the two preceding steps (4.37 ± 0.12 g and 4.58 ± 0.11 g) compared to the PIVOT step (4.10 ± 0.09 g). Larger peak joint flexion angular velocities were observed at PRE step (ankle: 367 ± 192 deg.s−1; knee 493 ± 252 deg.s−1) compared to PIVOT step (ankle 255 ± 183 deg.s−1; knee 377 ± 229 deg.s−1). Turn intensity did not influence peak GRF at PIVOT step. This study highlights the importance of steps prior to turning and their high-frequency loading characteristics. It is suggested that investigations of lower limb loading during turning should include this deceleration phase and not focus solely on pivot FGC.

Mechanical Player Load™ using trunk-mounted accelerometry in football: Is it a reliable, task- and player-specific observation?

ABSTRACT The aim of the present study was to examine reliability and construct convergent validity of Player Load™ (PL) from trunk-mounted accelerometry, expressed as a cumulative measure and an intensity measure (PL · min–1). Fifteen male participants twice performed an overground football match simulation that included four different multidirectional football actions (jog, side cut, stride and sprint) whilst wearing a trunk-mounted accelerometer inbuilt in a global positioning system unit. Results showed a moderate-to-high reliability as indicated by the intra-class correlation coefficient (0.806–0.949) and limits of agreement. Convergent validity analysis showed considerable between-participant variation (coefficient of variation range 14.5–24.5%), which was not explained from participant demographics despite a negative association with body height for the stride task. Between-task variations generally showed a moderate correlation between ranking of participants for PL (0.593–0.764) and PL · min–1 (0.282–0.736). It was concluded that monitoring PL® in football multidirectional actions presents moderate-to-high reliability, that between-participant variability most likely relies on the individual’s locomotive skills and not their anthropometrics, and that the intensity of a task expressed by PL · min–1 is largely related to the running velocity of the task.

Biomechanics of the ski cross start indoors on a customised training ramp and outdoors on snow

An effective start enhances an athletes chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44 N), higher resultant impulse (0.114 Ns/kg), and knee joint range of motion (12°) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.

The effect of medially and laterally wedged insoles on lateral ankle stability during sidestepping movements

Since the start of the study in April 2009, 189 runners were included in the study. A total of 38% (n1⁄4 71) of the subjects completed their participation, whereas 34% (n1⁄4 64) were either excluded from, or dropped out of the study. Currently (1 February 2011), 54 subjects (28%) are actively involved in the study. A total of 35% of the subjects (25 of 71) who completed the study developed an overuse injury. Nine of the 25 runners developed an overuse symptomatic located at the knee joint. Twelve of 25 subjects showed overuse reactions at the foot (e.g. plantar fasciitis, Achilles tendonitis or shin splints). Four subjects developed an overuse injury located at the hip joint. The training logs enabled us to see/showed differences between healthy and injured runners based on the type of training session. Symptomatic runners completed more interval training sessions and competitions. No differences were found for running distance, training frequency and running time per week. Furthermore, no discrepancies were found between the use of neutral or supported footwear or reported running surface. Differences in ankle kinematics were found between the two groups. Significant differences were found in the barefoot condition, for both frontal and sagittal ankle motion, mainly between the nonsymptomatic runners and the runners injured at the knee joint.