Effects of rate of force development on EMG amplitude and frequency.

The purpose of this study was to compare the amplitude and frequency of the gastrocnemius EMG during ramp and ballistic contractions in highly trained sprint athletes. Sixteen female sprinters performed ramp and ballistic isometric contractions on a Biodex dynamometer. RMS and median frequency of the gastrocnemius EMG signals were obtained at the following torque levels: 25 +/- 5 %, 50 +/- 5 %, 75 +/- 5 %, 100 % MVC. The average rate of force development (RFD), was 610.2 +/- 123.1 N . m/s and 212.3 +/- 155.6 N . m/s for the ballistic and ramp contractions, respectively. In the ramp contractions the EMG amplitude increased as a function of torque. In the ballistic contractions the EMG amplitude decreased from 25 % to 100 % MVC. The highest RFD of 889.45 N . m/s was generated in ballistic contractions by a muscular activation pattern with high EMG amplitude (475.7 microV) and low frequency (116.7 Hz) at 25 % MVC. The findings suggest that the CNS utilizes different muscular activation patterns to modulate RFD in ramp and ballistic contractions. In ramp contractions the EMG amplitude increased linearly with force. In ballistic contractions a high RFD is generated with a muscular activation pattern consisting of high amplitude and low frequency at the start of the contraction.

Neural, metabolic, and performance adaptations to four weeks of high intensity sprint-interval training in trained cyclists.

The purpose of this study was to investigate the effects of short-term, high-intensity sprint training on the root mean squared (RMS) and median frequency (MF) derived from surface electromyography (EMG), as well as peak power, mean power, total work, and plasma lactate levels in trained cyclists when performed concurrently with endurance training. Seventeen trained cyclists were randomly assigned to a sprint training (S) group (n = 10, age 25 +/- 2.0 y) or a control (C) group (n = 7, age 25 +/- 0.5 y). Sprint training was performed bi-weekly for four weeks, comprising a total of 28 min over the training period. EMG measurements were taken before and after training during a series of four 30-s sprints separated by four minutes of active recovery. Plasma lactate, peak power, mean power, and total work were measured during each sprint bout. Following sprint training a significant increase occurred in the RMS of the vastus lateralis with a decrease in MF of the same muscle. Values for the vastus medialis did not change. Pre training exercising plasma lactate values were higher (p < 0.05) in C compared to S, but did not change with training. Exercising plasma lactate values increased (p < 0.05) from pre to post training in S, but were not different from C post training. Total work output increased from pre to post in S (p = 0.06). Peak power, mean power, and V.O (2)max increased (p < 0.05) pre to post training in S and C, indicating C was not a true control. In conclusion, these data suggest that four weeks of high-intensity sprint training combined with endurance training in a trained cycling population increased motor unit activation, exercising plasma lactate levels, and total work output with a relatively low volume of sprint exercise compared to endurance training alone.

Effects of tape and exercise on dynamic ankle inversion.

OBJECTIVE: To compare the effects of tape, with and without prewrap, on dynamic ankle inversion before and after exercise. DESIGN AND SETTING: Doubly multivariate analyses of variance were used to compare the taping and exercise conditions. Subjects were randomly assigned to a fixed treatment order as determined by a balanced latin square. The independent variables were tape application (no tape, tape with prewrap, tape to skin) and exercise (before and after). The dependent variables were average inversion velocity, total inversion, maximum inversion velocity, and time to maximum inversion. SUBJECTS: Thirty college-age male and female students (17 males, 13 females; mean age = 24.9 +/- 4.3 years, range, 19 to 39 years) were tested. Subjects were excluded from the study if they exhibited a painful gait or painful range of motion or had a past history of ankle surgery or an ankle sprain within the past 4 weeks. MEASUREMENTS: We collected data using electronic goniometers while subjects balanced on the right leg on an inversion platform tilted about the medial-lateral axis to produce 15 degrees of plantar flexion. Sudden ankle inversion was induced by pulling the inversion platform support, allowing the platform support base to rotate 37 degrees . Ten satisfactory trials were recorded on the inversion platform before and after a prescribed exercise bout. We calculated total inversion, time to maximum inversion, average inversion velocity, and maximum inversion velocity after sudden inversion. RESULTS: We found no significant differences between taping to the skin and taping over prewrap for any of the variables measured. There were significant differences between both taping conditions and no-tape postexercise for average inversion velocity, maximum inversion, maximum inversion velocity, and time to maximum inversion. The total inversion mean for no-tape postexercise was 38.8 degrees +/- 6.3 degrees , whereas the means for tape and skin and for tape and prewrap were 28.3 degrees +/- 4.6 degrees and 29.1 degrees +/- 4.7 degrees , respectively. After exercise, inversion increased by 1.0 degrees +/- 2.8 degrees for the no-tape condition, whereas the tape-to-skin and tape-over-prewrap inversion increased by 2.1 degrees +/- 3.2 degrees and 1.7 degrees +/- 2.2 degrees , respectively. CONCLUSIONS: There was no difference in the amount of inversion restriction when taping with prewrap was compared with taping to the skin. Tape and tape with prewrap significantly reduced the average inversion velocity, maximum inversion, maximum inversion velocity, and the time to maximum inversion. Both taping conditions offered residual restriction after exercise.

Effects of high-top and low-top shoes on ankle inversion.

OBJECTIVE: To determine the differences in the rate and amount of ankle inversion in subjects wearing high-top and low-top shoes. DESIGN AND SETTING: Subjects were filmed at 60 Hz while on an inversion platform that suddenly inverted the right ankle 35 degrees . We measured 5 trials of sudden inversion for each subject in high-top and low-top shoes. SUBJECTS: Twenty male subjects with no history of lower leg injury within the previous 6 months. MEASUREMENTS: We measured ankle inversion using video motion analysis techniques at 60 Hz. A2 x 5 factorial repeated- measures analysis of variance was used to test for significant differences in the amount of inversion, average rate of inversion, and maximum rate of inversion. RESULTS: The high-top shoes significantly reduced the amount and rate of inversion. The high-top shoes reduced the amount of inversion by 4.5 degrees , the maximum rate of inversion by 100.1 degrees /s, and the average rate of inversion by 73.0 degrees /s. CONCLUSIONS: The high-top shoes were more effective in reducing the amount and rate of inversion than the low-top shoes. Depending upon the loading conditions, high-top shoes may help prevent some ankle sprains.

Immediate and residual changes in dorsiflexion range of motion using an ultrasound heat and stretch routine.

OBJECTIVE: With respect to increasing ankle dorsiflexion range of motion, our objective was to examine the influence, if any, of preheating the triceps surae with ultrasound before stretching. DESIGN AND SETTING: Subjects were assigned to either group A (ultrasound and stretch) or group B (stretch alone). Group A received 3-MHz ultrasound (1.5 W/cm(2), 4 times effective radiating area) for 7 minutes to the musculotendinous junction of the triceps surae before stretching. Group B rested for 7 minutes before stretching. Both groups then performed identical calf stretches for 4 minutes. Treatment for both groups was conducted at the Brigham Young University Sports Injury Research Laboratory twice daily for 5 days with at least 3 hours between procedures. We analyzed the data with a 2 x 3 x 10 factorial analysis of variance with repeated measures. A Tukey post hoc test was used to identify significant differences in range of motion. SUBJECTS: Forty college students (male = 18, female = 22, age = 20.4 +/- 2.5 years) volunteered for the study. MEASUREMENTS: Maximal ankle dorsiflexion range of motion was measured using an inclinometer before and after each treatment. RESULTS: Immediate effects were that ultrasound and stretch increased mean dorsiflexion range of motion in all sessions significantly more than stretch alone in three treatment sessions. Residual effects were that dorsiflexion range of motion increased 3 degrees in both groups after nine treatment sessions; however, neither group significantly outperformed the other. CONCLUSION: As studied, an ultrasound and stretch routine may increase immediate range of motion more than stretch alone, possibly enhancing performance in practice and competition. This increased range of motion, however, is not maintained over the long term and is not more than the range of motion gained from stretching alone. A similar study using subjects with decreased range of motion after immobilization or injury should be conducted to see if the ultrasound and stretch regimen would produce lasting range-of-motion increases.

An electromyographic investigation of 4 elastic-tubing closed kinetic chain exercises after anterior cruciate ligament reconstruction.

OBJECTIVE: To determine the electromyographic (EMG) activity of the vastus medialis oblique (VMO), vastus lateralis (VL), semitendinosus and semimembranosus (ST), and biceps femoris (BF) muscles during 4 elastic-tubing closed kinetic chain exercises in postoperative patients with anterior cruciate ligament (ACL)-reconstructed knees. DESIGN AND SETTING: A 4 x 4 repeated-measures analysis of variance design guided this study. Independent variables were type of exercise and muscle; the dependent variable was EMG activity. SUBJECTS: Fifteen patients, 5 to 24 weeks after ACL reconstruction. MEASUREMENTS: Subjects performed 4 exercises (front pull, back pull, crossover, reverse crossover) with elastic tubing attached to the foot of the uninjured leg. Time-and amplitude- normalized EMG activity was recorded from the VMO, VL, ST, and BF muscles of the injured leg. The hamstrings: quadriceps ratio was calculated. RESULTS: The normalized VMO, VL, and BF EMG activity ranged from 25% to 50% of maximum voluntary isometric contraction for the 4 exercises. The ST ranged from 12% on the back pull to 58% on the front pull. The hamstrings: quadriceps ratios were 137% (front pull), 115% (crossover), 70% (back pull), and 60% (reverse crossover). CONCLUSIONS: We suggest that clinicians use these exercises during early ACL rehabilitation since they incorporate early weightbearing with hamstring and quadriceps coactivation.

The effects of high-volt pulsed current electrical stimulation on delayed-onset muscle soreness.

OBJECTIVE: We investigated three 30-minute high-volt pulsed current electrical stimulation (HVPC) treatments of 125 pps to reduce pain, restore range of motion (ROM), and recover strength loss associated with delayed-onset muscle soreness (DOMS). DESIGN AND SETTING: Randomized, masked comparison of three 30-minute treatment and sham HVPC regimens over a 48-hour period. SUBJECTS: Twenty-eight college students. MEASUREMENTS: Subjects performed concentric and eccentric knee extensions with the right leg to induce muscle soreness. Assessments were made before and after the exercise bout and each treatment at 24, 48, and 72 hours postexercise. RESULTS: Three separate 2 x 3 x 2 ANOVAs were used to determine significant differences (p < .05) between days, treatments, and pre-post treatment effects and significant interaction among these variables. Scheffe post hoc tests showed no significant reduction in pain perception or improvement in loss of function at 24, 48, and 72 hours postexercise. Mean pain perception assessments (0 = no pain, 10 = severe pain) for the HVPC group were 2.9, 4.5, and 3.5 and for the sham group 3.8, 4.8, and 3.5). Mean ROM losses for the HVPC group were 9.0 degrees , 22.3 degrees , and 26.2 degrees , and for the sham group were 9.5 degrees , 23.1 degrees , and 23.0 degrees . Mean strength losses (1RM) for the HVPC group were 25.9, 25.7, and 20.8 lbs and for the sham group were 22.3, 22.3, and 13.8 lbs. CONCLUSIONS: HVPC as we studied it was ineffective in providing lasting pain reduction and at reducing ROM and strength losses associated with DOMS.

The effects of spatting and ankle taping on inversion before and after exercise.

OBJECTIVE: To compare the effects of spatting, taping and spatting, taping, and not taping on the amount and rate of inversion of the ankle before and after exercise. DESIGN AND SETTING: We filmed subjects at 60 Hz while they stood on a platform that suddenly inverted the right ankle. Five trials were measured before and after a 30-minute period of drills. SUBJECTS: We tested 15 male rugby players with no history of lower-leg injury within the previous 6 months limiting activity for more than 2 days. MEASUREMENTS: The amount and rate of inversion in the four conditions were digitized and analyzed. RESULTS: The combination of spatting and taping was the most effective in reducing inversion rate and range of motion before and after exercise. CONCLUSIONS: All three taping treatments were effective in reducing the amount and rate of inversion. Exercise loosened the tape, but there may be a functional restriction of the amount and rate of inversion after exercise.

Rate of Temperature Decay in Human Muscle Following 3 MHz Ultrasound: The Stretching Window Revealed.

Researchers have determined that when therapeutic ultrasound vigorously heats connective tissue, it can be effective in increasing extensibility of collagen affected by scar tissue. These findings give credence to the use of continuous thermal ultrasound to heat tissue before stretching, exercise, or friction massage in an effort to decrease joint contractures and increase range of motion. Before our investigation, it was not known how long following an ultrasound treatment the tissue will remain at a vigorous heating level (>3 degrees C). We conducted this study to determine the rate of temperature decay following 3 MHz ultrasound, in order to determine the time period of optimal stretching. Twenty subjects had a 23-gauge hypodermic needle microprobe inserted 1.2 cm deep into the medial aspect of their anesthetized triceps surae muscle. Subjects then received a 3 MHz ultrasound treatment at 1.5 W/cm(2) until the tissue temperature was increased at least 5 degrees C. The mean baseline temperature before each treatment was 33.8 +/- 1.3 degrees C, and it peaked at 39.1 +/- 1.2 degrees C from the ultrasound. Immediately following the treatment, we recorded the rate at which the temperature dropped at 30-second intervals. We ran a stepwise nonlinear regression analysis to predict temperature decay as a function of time following ultrasound treatment. We found a significant nonlinear relationship between time and temperature decay. The average time it took for the temperature to drop each degree as expressed in minutes and seconds was: 1 degrees C = 1:20; 2 degrees C = 3:22; 3 degrees C = 5:50; 4 degrees C = 9:13; 5 degrees C = 14:55; 5.3 degrees C = 18:00 (baseline). We conclude that under similar circumstances where the tissue temperature is raised 5 degrees C, stretching will be effective, on average, for 3.3 minutes following an ultrasound treatment. To increase this stretching window, we suggest that stretching be applied during and immediately after ultrasound application.

Foot placement angle and arch type: effect on rearfoot motion.

The purpose of the study was to describe the relationship between foot placement angle, arch type, and rearfoot motion during running. Twenty women were filmed in the frontal plane at 100 fps. Subjects displaying a variety of foot placement angles were chosen. Before data collection, arch indices were calculated. Each subject ran five trials at a pace of 3.5 m/sec. All subjects wore the same type of shoe. All trials were digitized to determine rearfoot angles throughout foot contact. The following mean values were obtained: total rearfoot was 10.09 degrees, maximum pronation was -9.63 degrees, foot placement angle was 7.58 degrees and arch index (AI) was 0.23 cm2. Non-linear regression was used to predict the relationship between maximum pronation and total rearfoot motion using foot placement angle and AI. Foot placement angle was the best single predictor of total rearfoot motion. When using both foot placement angle and arch type as predictors of total rearfoot motion, r2 was .35. Less abduction was associated with more total rearfoot motion. Arch type exhibited a quadratic relationship with total rearfoot motion. Normal-arched individuals (.21 cm2 less than AI less than .26 cm2) exhibited less total rearfoot motion than high-arched (AI greater than .26 cm2) and flat-arched (AI less than .21 cm2) individuals. For maximum pronation, foot placement angle was the only significant predictor (r2 = .13). Greater foot placement angles (more abduction) were associated with less maximum pronation.