Measurement of fibre pennation using ultrasound in the human quadriceps in vivo

Summary Real-time ultrasound scanning was used to measure the angles of fibre pennation of vastus lateralis (VL) and vastus intermedius (VI) of the human quadriceps (n = 12) in vivo. The maximum isometric force and cross-sectional area of the quadriceps were also measured. With the knee at right-angles the mean fibre angles for VL and VI respectively were 0.133 (0.021) rad [7.6° (1.2°)] and 0.143 (0.028) rad [8.2° (1.6°)] [mean (SD)], which is within the range of angles measured on cadavers. The mean angle decreased in going from the contracted [VL, 0.244 rad (14°); VI, 0.279 rad (16°)] to the stretched [VL, 0.105 rad (6°); VI, 0.122 rad (7°)] position. There was a significant positive correlation between fibre angle and muscle cross-sectional area but no relationship between fibre angle and force per cross-sectional area. No increase in fibre angle was detected after 3 months strength training. We conclude that ultrasound can be used to measure pennation angles of superficial muscle groups but we could not demonstrate a relationship between pennation and force-generating capacity.     

Effect of diet on human muscle weakness following prolonged exercise

Summary The effect of altering muscle glycogen on the ability of skeletal muscle to generate voluntary and electrically evoked isometric force following prolonged exercise has been investigated in five healthy male subjects. Measurements from the triceps surae were made at rest, and before and after prolonged exercise (uphill walking) at approximately 75% in low muscle glycogen (low CHO) and high muscle glycogen (high CHO) conditions.The results showed that before exercise there was no change in maximal twitch tension ( ), maximal tetanic tension at frequencies of 10 (P_o10), 20 (P_o20) and 50 Hz (P_o50), and maximal voluntary contraction (MVC) in low and high CHO compared with normal. The loss of force during a 2 min electrically evoked fatigue test at rest was found to be higher (p<0.05) in low CHO and lower (p<0.05) in high CHO than normal.Following the prolonged exercise, muscle weakness was produced in both low and high CHO conditions, but was found to be significantly greater in the low CHO condition for the measurements of P_o10 (p<0.01), P_o20 (p<0.05) and MVC (p<0.05).It is concluded that changes in muscle glycogen alone do not alter the isometric force generating capacity of human muscle, but when combined with prolonged exercise low muscle glycogen enhances exercise-induced muscle weakness.     

Alterations of mechanical characteristics of human skeletal muscle during strength training

Summary To investigate the influence of strength training on the mechanical characteristics of human skeletal muscle, 14 male subjects went through training of combined heavy concentric and eccentric contractions three times a week for 16 weeks. The strength training program consisted mainly of dynamic exercises for leg extensors with loads of 80 to 120% of one maximum repetition. The force-time curves produced during various vertical jumps were the basis for calculation of various mechanical parameters. In addition to a great increase (p<0.001) in maximal isometric force, heavy resistance strength training also caused significant (p<0.05–0.01) increases in heights and in various mechanical parameters in positive work phases of vertical and drop jumps. The increase in positive force during a fast dynamic contraction was correlated (p<0.01) with the reduced time to produce a certain submaximal force level in isometric condition. No changes in the elastic properties of the muscle were observed as judged from the difference between the counter-movement and squat jumps. When the training was followed by the 8-week detraining period a great decrease (p<0.001) in maximal force took place, but only minor changes (ns) were observed in fast force production.Supported in part by the grants from The Finnish Olympic Committee and Central Sport Federation     

124例健康成人吸气肌强度和耐力测定

本文测定了124例健康成人最大吸气压和最大持续吸气压,探讨吸气肌强度和耐力的分布及影响因素。发现最大吸气压和最大持续吸气压受年龄、体重和性别响影,吸气肌张力时间指数0.30可作为检测吸气肌疲劳的临界阈值。     

Relationship Between Kinesthetic Aftereffects and "Strength of the Nervous System"

Investigators have traditionally assumed that the kinesthetic aftereffects (KAE) procedure measures individuals’tendencies either to augment or to reduce the impact of incoming stimulation. Strikingly, this putative difference between individuals is one of the bases of Pavlov's typology: Pavlov maintained that individuals with “strong” nervous systems resist incoming stimuli, while individuals with “weak”nervous systems are particularly sensitive to stimuli. The present study supports the usual interpretation of the KAE task by indicating significant relationships between it and three measures of “strength of the nervous system.”The present data also have a practical implication: Since the KAE procedure has recently undergone strong methodological attacks, these results suggest that an investigator interested in the construct in question (tendencies to augment or reduce stimuli) can employ the measures of strength rather than the KAE method.     

Isokinetic strength,endurance, and fiber type composition in elite American paddlers

Summary Muscle fiber type and isokinetic strength and fatigue were examined in nine highly trained canoe and kayak paddlers. Needle biopsies were taken from the right vastus lateralis and biceps brachii muscles and the samples stained for myofibrillar ATPase. Baseline elbow flexion and knee extension isometric (0·s^–1) and isokinetic (60·s^–1 or 1.05 rad·s^–1 and 180·s^–1 or 3.14 rad·s^–1) peak torques were determined. Each subject then performed two series of 50 isokinetic contractions at an angular velocity of 180·s^–1: elbow flexion and knee extension series, separated by 3 h. The percentage of slow twitch fibers was similar in the biceps brachii (43.9%) and the vastus lateralis (43.3%). The fast twitch/slow twitch fiber area ratio was significantly higher in the more highly trained biceps brachii due to larger FT fibers. No relationship was found between fiber type composition and baseline peak torques or decline in peak torque due to the fatigue regimens. Baseline peak torque correlated with initial strength level, body weight, and limb girth. The results suggested that for these paddlers muscle strength and the decline in strength induced by repetitive isokinetic contractions were more dependent on characteristics of body size than on fiber type composition.     

Does placing screws off-centre in tubular bone alter their pullout strength?

Screws are used to fix broken bones either directly or through plates. Surgeons sometimes find that a screw they have used is not quite in the centre of the bone but to one side or maybe even the edge. It has been postulated that screws catching the edge of the bone do not give good fixation and may even predispose to fractures.We conducted the present experiment using porcine femora to see if a screw's transverse plane position in the bone made any difference to its pullout strength. 20 cortical screws were inserted into the cortical segments of 5 pig femora (4 screws per femur) using the standard AO technique. The screws were inserted in one of 5 randomly chosen positions—centre, medial off-centre, lateral off-centre, medial edge and lateral edge. The screws were tested to failure in axial pullout using a Losenhausen universal testing machine.We found that 4 of the 8 ‘edge’ screws failed with fractures developing around the screw track during pullout testing. These 4 screws were noted on cross-section to have 100% bone contact with their threads completely embedded in the cortical bone. They also had significantly lower pullout resistance than the 4 ‘edge’ screws without fractures (p = 0.05) and the 12 ‘non-edge’ screws (in the central 75% of the bone) (p = 0.03). This was most likely due to the associated fractures. There was a statistically significant association between the ‘edge’ screw position (i.e. within 12.5% of the medial or lateral edge of the bone) and the likelihood of fracture (p = 0.000).We conclude that in the transverse plane, cortical screws either on their own or through plates should be inserted in the central three-fourths of the bone. Screws placed outside this zone carry a higher risk of fixation failure due to fractures around the screw track with axial loading.     

Effects of aquatic resistance training on health and fitness in postmenopausal women

To investigate effects of 24 weeks of resistance training with aquatic resistance devices or elastic bands (EB) on markers of cardiovascular health and physical capacity. Forty-six healthy, sedentary postmenopausal women participated. The groups were aquatic exercise (AE; n = 15), EB (n = 21), and control (n = 10). Venous blood chemistry included cholesterol, triglycerides, glucose, and apolipoprotein B. Physical capacity was assessed by the sit-and-reach, knee push-up, 60-s squat, and abdominal crunch tests. Both AE and EB, respectively, showed a significant (P ≤ 0.05) decrease in body fat (14.56, 11.97%) and diastolic blood pressure (8.03, 5.88%), and a significant increase in fat-free mass (2.88, 1.22%), sit-and-reach (27.94, 44.2%), knee push-ups (84.74, 51.59%), and 60-s squats (65.76, 46.04%). AE also showed a significant increase in abdominal crunches (28.11%). Aquatic resistance training can offer significant physiological benefits in health and performance that are comparable to those obtained from EB in this population.     

光固化冠桥复合树脂强化作用的实验研究

目的：探讨光固化冠桥复合树脂的强化效果，方法：选择3种光固化冠桥树脂，3种不同目数的涤纶和3种不同目数的不锈钢筛网作外加强，制作试件及冠桥，并主用纤维网加强桥相比，测定抗压、3眯抗弯强度。结果（1）不锈钢丝网增强效果明显，涤纶丝周无强化效果。（2）冠加强的效果尤为明显；（3）Targis的性质好于Artalss和Solidex。结论复合材料的性能与外加强材料密切相关，金属网状结构对压缩的耐受性优于对屈曲的耐受性。     

喷磨预处理牙釉质对树脂粘结强度的影响

目的 观测釉质轻空气喷磨预处理后对树脂粘结性能的影响。方法 分别对30颗离体牙的牙釉质进行喷磨、喷磨加酸蚀、单纯酸蚀后粘结树脂,测定其剪切强度。用方差检验进行统计分析。结果 酸蚀加空气喷磨,并不影响常规的树脂与釉质的粘结强度。但单独的空气喷磨,可提高树脂与釉质的粘结强度。结论 临床上可采用空气喷磨预处理牙釉质,不必再行常规的酸蚀处理牙釉质。