MODIFICATIONS IN JOINT KINETICS DURING STOP AND GO
LANDING MOVEMENTS UNDER FATIGUED AND NON-FATIGUED CONDITIONS

J. L. McNitt-Gray, J. P. Eagle, S. Elkins, and B. A. Munkasy
Biomechanics Research Laboratory
University of Southern California
Los Angeles, CA 90089-0652

Presented at the 20th Annual Meeting of the American Society of Biomechanics
Atlanta, Georgia. October 17-19, 1996

INTRODUCTION

The large reaction forces (3.5 to 14 times body weight) encountered during landings has been associated with the high incidence of injury associated with landing activities (NCAA, 1986, 1990). However, methodological limitations associated with load distribution and tolerance of anatomical structures, have prohibited development of a clear-cause effect relationship between load and injury (Nigg & Bobbert, 1990). Examination of mechanisms athletes use to attenuate the reaction forces experienced during landings under realistic practice and competitive conditions may assist in establishing a causal relationship between load and injury.

In this study, the intended movement following a landing and the level of fatigue were hypothesized to influence mechanics and loading characteristics of landings performed by female collegiate basketball players. This hypothesis was tested by examining reaction force characteristics, joint kinetics, and muscle activation patterns between three realistic rebounding movements: land and stop (LS), land and go (LG), and land and go under moderately fatigued conditions (LGF). All three tasks required visual interaction with a basketball suspended over head.

PROCEDURES

Collegiate female basketball players (n=7) volunteered to serve as subjects. During data collection, subjects were asked to land three different rebounding tasks (LS, LG, LGF) using their own self-selected landing strategy. LS and LG tasks were blocked and randomized between subjects. All LGF tasks were performed as the final task of the data collection session. The basketball players performed the LS task by jumping from a stationary position on the floor, palming the center of a suspended basketball located 0.41 m above their stand and reach height, and landing on a force plate. During LG tasks, each subject repeated the LS movement and then immediately performed a second vertical jump while reaching for a second ball located at 90% of the individual's preseason maximum vertical jump and reach height. During the LGF tasks, moderate fatigue specific to jumping was induced immediately prior to the performance of the LG task by requiring the subject to perform maximum vertical jumps once every three seconds, until they were unable to obtain 80% of their maximum vertical jump and reach height.

Reaction forces measured at the shoe-plate interface were quantified at 800 Hz (Kistler force plates). Sagittal plane kinematics were recorded simultaneously using high speed video (200 fps; NAC Motion Analysis System). Activity of the soleus (SO), medial gastrocnemius (MG), vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), gluteus maximus (GM), and semitendinosis (ST) were monitored using surface electrodes (1600 Hz, Beckman silver-silver chloride electrodes, Differential amps, Data, Inc.). Location of the center of pressure relative to the feet was determined by locating the force plate in the kinematic reference system. Each coordinate of the body landmarks (Zatsiorsky et al., 1987) were digitized (Peak Performance, Inc.) and filtered using a fourth order Butterworth Filter (Saito & Yokoi, 1982) using a cut-off frequency determined by Jackson (1979). The EMG signals from each muscle were processed as specified by the International Society of Electrokinesiology (ISEK, 1985) using high and low pass filters, rectified, normalized within muscle, and integrated during intervals prior to and during the landing. Synchronized kinematic and reaction force data were used to calculate the net joint forces and moments for the ankle, knee, and hip of the leg closest to the camera using Newtonian mechanics. Significant differences in normalized kinematics, reaction forces, joint kinetics, and EMG integrated over 25 ms bins (IEMG) were compared between tasks using within subject analysis of variance techniques (p< 0.05).

RESULTS AND DISCUSSION

The small variance and absence of significant differences in vertical velocity of the total body center of mass at contact between trials and subjects confirmed the experimental tasks constraints were successful in minimizing differences in vertical velocity at contact. Reaction force and net joint moment characteristics observed in this study were similar to those observed by Devita and Skelly (1992) and McNitt-Gray (1991). Within subject observations indicated, two of seven subjects demonstrated consistent increases in peak vertical force with fatigue and five of seven subjects demonstrated greater side-to-side differences in peak vertical reaction forces with fatigue. Significant differences in time to resultant peak vertical forces were also observed between LS and LG tasks. During the propulsive phase of the go movements (LG, LGF), the reaction force impulse and integrated muscle activity were more pronounced than during the LS tasks (Figure 1) .

Muscle activation patterns (IEMG) during landing tended to be consistent within subjects over the majority of trials. After accounting for a 50 ms electromechanical delay, the IEMG corresponded to the net joint moments (Figure 1). Activity of the MG was observed prior to contact. Activity of the RF, VM, VL were also observed together with knee extensor net joint moments. During the period when the knee and hip demonstrated extensor net joint moments, GM and RF activity were observed together and the ST tended to be more active in the LGF tasks than in the LS and LG tasks. Activation of biarticular muscles observed during periods where adjacent joints demonstrated opposite directions in net joint moment power, create the potential for energy transfer (Prilutsky & Zatsiorksy, 1994).

From these data, movements performed following landings do not significantly loading characteristics during the landing phase. Inducing moderate fatigue tended to increase the variability of loading characteristics. Effective coupling and loading implications during the transistion between the landing phase and the initiation of the go movements requires further investigation.

REFERENCES

Devita, P. & Skelly. MSSE, 24, 108-15. 1992.

ISEK Standards, 1985.

Jackson, K, IEEE Trans Biomed. Eng, 26, 122-4, 1979.

McNitt-Gray, J., J of Biomech., 26, 1037-46, 1993.

NCAA Injury surveil. System, 1986, 1990.

Prilutsky, B.I. & Zatsiorsky, V. M., J. Biomech, 27(1), 25-34, 1994.

Saito, S., & Yokoi, T. Bull. of Hlth & Sport Sci, U of Tsukuba, 5, 201-206, 1982.

Zatsiorsky, V., Seluyanov, V., & Chugunova, L.G. Contemp. problems of biomech, 272-289, 1988.

ACKNOWLEDGMENTS

This project was funded in part by the NCAA. Basketball shoes were generously provided by Converse. The authors would like to thank members of the USC Basketball program, Michelle Welch, Jacki Heino, Terry Smith, Dawn Irvine, and the undergraduate research assistants in the USC Biomechanics lab for their assistance with this project.