ABSTRACT
Objective To study the differences in physical characteristics of lacrosse balls and baseballs, so as to investigate the potential sports injuries caused by lacrosse balls. Methods Twelve lacrosse balls and 12 baseballs were used as testing samples. All testing balls were under conditioning control for 24 h to make sure temperature and humidity were consistent before measurement. The physical characteristics such as ball weight, circumference, compression-displacement and restitution coefficient were measured, respectively. Independent-sample t-test was used to compare the differences in lacrosse balls and baseballs. Results The lacrosse ball weighted (144.65±0.29) g, and its circumference, compression-displacement, and restitution coefficient were (19.97±0.02) cm, (91.76±1.23) kg and (0.633±0.011), respectively. The baseball weighted (146.12±0.45) g, and its circumference, compression-displacement and restitution coefficient were (23.20 ± 0.06) cm, (124.76±1.68) kg, and (0.528 ± 0.005), respectively. The lacrosse balls are significantly smaller in weight, circumference and compression-displacement than the baseballs (P<0.05). The restitution coefficient was significantly greater than baseballs (P<0.05). Conclusions The physical characteristics of lacrosse balls are in compliance with international standard. However, lacrosse balls have the same risk of causing serious injuries as baseballs. To reduce the risk of sports injuries, it is recommended that the specification of lacrosse balls need to be classified for different age and skill levels.
ABSTRACT
Objective To investigate the effect of a novel hip flexor training machine on muscle activation and range of motion (ROM) in lower limb under the condition of different resistances. Methods Six volunteers performed consecutive rightly hip flexion and extension for 30 times under light or heavy resistance randomly on the training machine, and the muscle activity and ROM in lower limb during the movement were measured at the same time. Results The muscle activation of rectus abdominal, hip flexor muscles, gluteus maximum, rectus femoris and biceps femoris under heavy resistance was significantly higher than that under light resistance (P<0.05); the muscle activation of rectus abdominis, hip flexor muscles and rectus femoris at during the last 3 times were significantly higher than that at of the first 3 times under heavy resistance (P<0.05); under light resistance, only the muscle activation of erector spinae and rectus femoris during the last 3 times were significantly higher than that of the first 3 times. The ROM and angle of hip extension under heavy resistance were significantly smaller than those under light resistance. Conclusions Under the rational ROM of hip joint, this new hip flexor training machine can stimulate the hip flexion and extension muscles and other co-contraction muscles to accomplish the movement, especially under the condition of heavy resistance.