Year

2002

Degree Name

Master of Science (Hons.)

Department

Department of Biomedical Science

Abstract

There is a high incidence of knee injuries in sports that involve excessive and repetitive loading of the body. It is these excessive and repetitive loads that have been identified as a primary risk factor in the development of the commonly occurring knee injury known as patellar tendinosis. It has been suggested that neuromuscular fatigue may interfere with the ability of the patellar tendon to sustain repetitive loads by decreasing the ability of the lower limb to function optimally and to efficiently dissipate the external loads sustained during landing, thereby increasing the risk of developing patellar tendinosis. However, there is a paucity of research examining the effects of fatigue on the landing mechanics in movement tasks known to be associated with patellar tendinosis. Therefore, the purpose of this study was to establish if the landing phase of a spike jump movement (SJM) performed from ground level and a drop jump movement (DJM) performed from a standard bench height differed with respect to landing mechanics, and if fatigue induced by repetitive standing vertical jumps altered the landing mechanics of either experimental task.

Fourteen healthy uninjured subjects (mean age = 26.5 ± 5.6 years) performed two experimental tasks, a SJM and a DJM , in a non-fatigued and a fatigued condition that involved the subject landing on their dominant limb onto a sand surface. Subjects were fatigued by performing a series of weighted standing vertical jump sets, with pre- and post-fatigue blood lactate samples taken. During each trial, the subjects' sagittal plane motion was recorded using a Northern Digital OptoTrak Position Sensor (500 Hz), and the ground reaction forces generated at landing were recorded (1000 Hz) using a Kistler Multichannel force platform. For each subject's dominant limb, electromyographic activity was recorded using a Noraxon Telemyo transmitter and receiver (1000 Hz) for vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF), semitendinosus (ST) and medial gastrocnemius (MG). Time synchronisation of the kinetic, kinematic and electromyographic data was performed using Northern Digital OptoTrak Data Aquistion Unit II.

Analysis of all the variables showed that the two movements, the SJM and the DIM, displayed distinct landing mechanics. That is, during the DJM , subjects generated a significantly higher peak resultant ground reaction force (FR), a shorter time to the peak FR, and a faster rate of loading of the ground reaction forces during landing than when performing a SJM. Furthermore, subjects displayed significantly different segmental motion and alignment during landing between the two experimental tasks. That is, during a DJM the subjects displayed a significantly higher peak vertical jump height, less knee joint flexion, a higher knee joint angular velocity, and a more vertically aligned tibia both at IC and at the time of the peak FR compared to when performing a SJM. The subjects also displayed less tibial angular displacement during landing, more plantar flexion at the ankle joint at the time of the peak FR, a higher ankle joint angular velocity at the time of the peak FR, a more horizontally aligned foot relative to the ground at IC, and a greater foot angular velocity at the time of the peak FR during a DJM compared to a SJM. Furthermore, the subjects exhibited significantly longer muscle burst durations for RF, VM , MG and BF; an earlier muscle burst onset time relative to IC for RF and VM ; an earlier peak VL activity relative to IC; a later peak muscle activity relative to the time of the peak FR for RF and VM ; and a later muscle burst offset time relative to IC for RF and VM . Despite these between-task differences, the muscle burst intensity displayed during landing did not significantly differ between the two movement tasks.

Based on the between-task comparisons it was concluded that the DJM and the SJM were significantly different from each other with respect to the ground reaction forces generated at landing, lower limb motion and alignment during landing in the sagittal plane, and the synchrony of the lower limb muscle activation patterns. Therefore, removing the take-off component from the SJM to isolate the landing phase for research purposes, as in the DJM , is not valid as the two movement tasks involve distinct landing mechanics.

In terms of fatigue effects, the subjects were truly fatigued following the fatigue protocol, as indicated by a significant decrease in their standing vertical jump height and an increase in their post-fatigue blood lactate concentration. Despite this fatigue there was no significant change in the ground reaction forces generated at landing. However, fatigue significantly altered the segmental motion and alignment with the subjects displaying a significantly lower knee joint angular velocity at IC and a more vertically aligned tibia both at IC and at the time of the peak FR compared to when non-fatigued. Many of the fatigue effects, however, were task specific. For example, the subjects displayed a higher foot angular velocity at the time of the peak FR during a DJM , a higher ankle joint angular velocity at the time of the peak FR during a DJM , less ankle joint dorsiflexion at the time of the peak FR during a SJM, and a more vertically aligned tibia both at IC and at the time of the peak FR during a SJM in a fatigued compared to a non-fatigued condition. Furthermore, in the SJM when fatigued, the subjects displayed a significant decline in their jumping performance, evident by displaying a lower peak vertical height of the greater trochanter compared to when non-fatigued. However, only minor changes were observed in the synchrony of the muscle activation patterns with a later muscle burst peak activity to IC for RF and VM and a later MG muscle burst peak activity relative to the time of the peak FR.

It was concluded that fatigue induced by a series of standing vertical jumps did not significantly alter the ground reaction forces, or the duration or activation times of lower limb muscles at landing. However, fatigue did alter lower limb motion and alignment, and the synchrony of the lower limb muscle activation patterns displayed by the subjects during landing although most of these were task specific. Of particular importance, was the significant decline in the peak vertical jump height attained by the subjects in the SJM when fatigued. This has direct implications in Beach Volleyball, both during competition and during training, in which players who repetitively perform a SJM may become fatigued, resulting in a decrease in their SJM performance. Furthermore, the decline in the subject's peak vertical jump height may decrease the time available to position their segments approximately to control the deceleration of landing and dissipate the same high impact loads that are experienced when not fatigued. As a result, this may expose the joints of the lower limb, predominantly those superior to the ankle joint such as the knee, to increased loads. How these changes to the lower limb motion and alignment and the synchrony of lower limb muscle activation patterns during landing following fatigue influence patellar tendon loading requires further investigation.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.