Acute effects of static stretching on peak torque and the hamstrings‐to‐quadriceps conventional and functional ratios

Recent evidence has shown acute static stretching may decrease hamstring‐to‐quadriceps (H:Q) ratios. However, the effects of static stretching on the functional H:Q ratio, which uses eccentric hamstrings muscle actions, have not been investigated. This study examined the acute effects of hamstrings and quadriceps static stretching on leg extensor and flexor concentric peak torque (PT), leg flexor eccentric PT, and the conventional and functional H:Q ratios. Twenty‐two women (mean ± SD age=20.6 ± 1.9 years; body mass=64.6 ± 9.1 kg; height=164.5 ± 6.4 cm) performed three maximal voluntary unilateral isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60 and 180°/s before and after a bout of hamstrings, quadriceps, and combined hamstrings and quadriceps static stretching, and a control condition. Two‐way repeated measures ANOVAs (time × condition) were used to analyze the leg extension, flexion, and eccentric PT as well as the conventional and functional H:Q ratios. Results indicated that when collapsed across velocity, hamstrings‐only stretching decreased the conventional ratios (P<0.05). Quadriceps‐only and hamstrings and quadriceps stretching decreased the functional ratios (P<0.05). These findings suggested that stretching may adversely affect the conventional and functional H:Q ratios.     

Muscle activation and torque development during maximal unilateral and bilateral isokinetic knee extensions

BACKGROUND: The aim of this study was to investigate whether or not a bilateral strength deficit occurs during bilateral (BL) velocity controlled dynamic knee extensions and if the neural control of the knee extensors and flexors is altered during homologous muscle BL efforts. METHODS: Twenty-eight healthy and habitually active subjects, 13 female and 15 male, performed maximal unilateral (UL) and BL isokinetic leg extensions at a velocity of 60 degrees.s-1 through a 90 degrees range of motion of the knee joint (90 to 180 degrees). Knee extension torque and electromyographic activity (EMG) of the quadriceps and hamstrings muscles were recorded. RESULTS: The mean knee extensor torque produced in the BL condition (168 +/- 52 Nm) was 17% less than the sum of the two UL conditions (Sigma=202 +/- 56 Nm). During BL conditions, quadriceps EMG activity was less in both legs (left, 8.2 +/- 7.4% less and right, 13.9 +/- 9.1% less, respectively). There were no significant differences between BL and UL efforts for either left or right hamstrings activity. Eighteen subjects, who when asked to perform a maximal knee extension simultaneously activated their contralateral hamstrings, had significantly higher bilateral deficits (21%) compared to those who exhibited little or no contralateral hamstrings EMG activity (14%). CONCLUSIONS: The main findings of the study were that a bilateral strength deficit occurred when simultaneously maximally activating the homologous knee extensor muscles. This deficit was in all likelihood due to a less than maximal efferent drive to the quadriceps muscles. Hamstrings EMG activity was not greater during the BL knee extensions, which supports the notion that antagonistic muscle activity was not primarily responsible for the observed bilateral deficit.     

Comparison of isokinetic peak force and work parameters in youth with and without mental retardation.

PURPOSE: The purpose of this study was to compare isokinetic knee (flexion and extension) strength of nondisabled youth (ND; 15 males, 15 females; males = 12.7 +/- 2 yr; females = 13.4 +/- 2 yr) and youths with mental retardations (MR, 17 males + 13 females; male = 14.7 +/- 2 yr; females = 13.6 +/- 2 yr). METHODS: Subjects were evaluated on a Kin-Con isokinetic dynamometer at a speed of 60 degrees x s(-1). Parameters measured were peak torque (PT), time to PT, angle of PT, total work (W), and PT hamstrings/quadriceps (HQ) ratio. Peak torque was also corrected by weight (BW) and body mass index (BMI). Peak torque, time to peak torque, angle of peak torque, and total work were analyzed using a 2 x 2 x 2 (groups x gender x muscle) repeated measures analysis of variance (MANOVA). Flexion/extension ratios, BMI, and BW were analyzed by separate 2 x 2 (group x gender) analyses of variance. RESULTS: Results of this study suggest that: 1) while gender differences are apparent in the ND population they are not evident in individuals with MR; 2) knee extension strength is higher for ND youth, thus causing lower PT HQ ratios when compared with those in youth with MR; 3) angle of PT and time to PT were similar among groups; and 4) total work performed is lower in individuals with MR. CONCLUSIONS: It was concluded that parameters of strength production in individuals with MR are not consistent and do not follow the same pattern as their nonretarded peers.     

Thigh muscle function after partial tear of the medial ligament compartment of the knee

The purpose of the study was to assess the isokinetic and isometric strength and power profile of the knees of 48 patients who had a previous second-degree sprain (partial tear) of the medial ligament compartment, the most common knee ligament injury in sports. The CYBEX II isokinetic dynamometer was used in the measurements. On an average of 8 yr after the injury, the mean strength deficit of the injured knees was minimal: 4 +/- 5% (range 0-28%) in extension and 2 +/- 4% (0-20%) in flexion. The average strength score (max. 100 points) was 90 +/- 11 (56-100), representing an excellent classification. In hamstrings, the relative strength deficit increased significantly with a higher speed of isokinetic movement (P less than 0.05). Compared with the strength parameters (peak torques), the other functional parameters of the injured knees (total work, average power, and peak torque acceleration energy) showed some but not significantly greater deficits (hamstrings 9-11%, quadriceps 6-8%). In conclusion, the general thigh muscle function in knees with old second-degree sprain of the medial ligament compartment appears good and acceptable, but the strength deficits are systematically greater in higher speeds of isokinetic movement. Therefore, rehabilitation utilizing high speed extension and flexion exercises is recommended.     

Fatigue after submaximal intensive stretch-shortening cycle exercise

OBJECTIVE: The aim of the present study was to examine some sites of neuromuscular fatigue after submaximal intensity stretch-shortening cycle exercise. METHODS: Twelve male subjects performed consecutive sledge jumps at 60% of maximal height until exhaustion (mean duration 443.7 s +/- 304.9 s, mean +/- SD). RESULTS: During the exercise, the blood lactate increased from 1.8 +/- 0.6 mmol x L(-1) (before exercise) to 6.1 +/- 1.7 mmol x L(-1) (P < 0.001) and serum creatine-kinase from 248 +/- 142 IU x L(-1) to 584 +/- 344 IU x L(-1) (P < 0.001). Electrical stimulation of the vastus lateralis and quadriceps femoris muscles to induce isometric knee extension resulted in decreased peak torque during single and double twitch after workout (from 22.1 +/- 6.3 Nm to 17.3 +/- 8.0 Nm, P < 0.05, and from 96.6 +/- 15.4 Nm to 76.2 x 19.8 Nm, P < 0.001, respectively), whereas there were no significant changes in contraction and relaxation times. Torque during 20-Hz stimulation decreased significantly (from 23.7 +/- 9.2 to 16.1 +/- 7.8 Nm, P < 0.01) but not at 100-Hz stimulation. During maximal voluntary isometric knee extensions, the rate of torque development was significantly (P < 0.01) more impaired than maximal torque (from 1619 +/- 390 Nm x s(-1) to 1,004 +/- 360 Nm x s(-1) and from 185 +/- 30.7 Nm to 151 +/- 32.3 Nm, respectively, both P < 0.001). At the same time, the muscle activation level increased by 15.8 +/- 24.1% (P < 0.05). The mean EMG amplitude of vastus lateralis during MVC increased by 34.9 +/- 39.2% (P > 0.05). CONCLUSION: It was concluded that after submaximal stretch-shortening exercise, the low-frequency fatigue occurred, very likely caused by lower Ca2+ release per single action potential.     

Weight loss, dietary carbohydrate modifications, and high intensity, physical performance

Well trained subjects (N = 12) were studied before and after losing approximately 6% of body weight to determine whether physical performance could be maintained while consuming a hypocaloric, high percentage carbohydrate diet. During a 4-d period of weight loss, subjects were randomly assigned to a high carbohydrate (HC) or low carbohydrate (LC) diet. A crossover design was used; subjects were measured before (PRE) and after (POST) weight loss on both diets for a 6-min bout of high intensity arm cranking, weight, skinfold thickness, and profile of mood states (POMS). Hemoglobin, hematocrit, and glycerol concentrations were analyzed for resting blood samples, while lactate, pH, and base excess were analyzed for blood samples drawn at rest and 1, 3, and 5 min after arm cranking. A three-way ANOVA of sprint work revealed a weight loss effect, a diet by weight loss interaction, and an order by diet by weight loss interaction (P less than 0.05). Total sprint work (mean +/- SE) PRE and POST HC was 37.7 +/- 2.1 kJ and 37.4 +/- 2.2 kJ, respectively. Sprint work was higher for PRE LC vs POST LC, with mean values of 37.4 +/- 2.1 kJ and 34.4 +/- 2.2 kJ, respectively. Post-arm cranking lactate was significantly higher PRE compared to POST for both HC and LC. Post-exercise blood pH was lower (P less than 0.05) at PRE vs POST, with no diet effect. Regardless of the diet, POMS variables tension, depression, anger, fatigue, and confusion were significantly elevated from PRE to POST; vigor was significantly lower.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eccentric and concentric isokinetic moment characteristics in the quadriceps and hamstrings of the chronic isolated posterior cruciate ligament injured knee

OBJECTIVE: Functional strength deficits associated with chronic isolated posterior cruciate ligament (PCL) insufficiency have received limited attention in the literature. The purpose of this study was to determine the eccentric and concentric isokinetic moment characteristics of the quadriceps and hamstrings in a sample of patients with isolated PCL injury. METHODS: Eccentric and concentric mean average and average peak moments were measured for 17 patients with a history of conservatively treated isolated PCL injury using an isokinetic dynamometer. Quadriceps and hamstring isokinetic moments were recorded from 10 degree to 90 degree of knee flexion. Strength ratios were calculated and compared with those reported in the literature for healthy subjects. RESULTS: The hamstrings of the involved side (eccentric/concentric (E/C) ratio = 1.06) were significantly weaker (p<0.05) eccentrically than those of the contralateral side (E/C ratio = 1.29). All hamstrings/quadriceps (H/Q) ratios were less than the universally accepted value of 0.60 and the eccentric H/Q ratio for the injured extremity was significantly lower than the non-injured (p<0.05). In a bilateral comparison, the injured/non-injured (I/N) ratio was less than 1.00 for concentric quadriceps, eccentric quadriceps, and hamstring isokinetic moments. Calculation of the E/C ratio showed that, for the quadriceps, it was 1.08 on the injured side and 1.07 on the non-injured extremity. CONCLUSIONS: Eccentric strengthening should be an integral part of functionally rehabilitating the quadriceps and hamstrings of athletes who suffer from the complications associated with chronic isolated PCL insufficiency.     

Bone mineral density and muscle strength in female ice hockey players

The purpose of this study was to investigate bone mineral density (BMD) at different sites in female ice hockey players as well as to study the relationship between BMD, muscle strength, and body composition parameters. The study group consisted of 14 female ice hockey players (age 22.2 +/- 4.3 years) which was compared with 14 inactive females (age 21.5 +/- 3.8 years). The two groups were matched for age and weight. Areal bone mineral density was measured in total body, head, lumbar spine, femoral neck, Ward's triangle and the trochanter, using dual energy X-ray absorptiometry. Body composition parameters were derived from the total body scan. Isokinetic concentric peak torque of the left quadriceps and hamstrings muscles was measured using an isokinetic dynamometer. Compared to the inactive group, the ice hockey players had significantly higher BMD of all of the bone sites measured, except for the head, (total body 6.9%, head -2.6%, lumbar spine 8.9%, femoral neck 17.6%, Ward's triangle 20.4%, and trochanter 21.7%). The hockey players also had significantly higher peak torque in the quadriceps and hamstrings muscles. In the ice hockey group, a significant positive correlation was found between BMD of the femoral neck and hamstrings peak torque at 225 degreesisecond (r = 0.67, P < 0.01). In the inactive group, significant positive correlations were found between BMD and peak torque in the hamstrings muscles (90 degrees/second: r = 0.6-0.8, P<0.05 (total body, trochanter) and P<0.01 (spine, neck), 225 degrees/second: r = 0.5-0.8, P<0.05 (total body, Ward's triangle, trochanter) and P< 0,01 (spine, neck)). In the inactive group significant positive correlations was also found between lean body mass and BMD of the trochanter (r = 0.58, P < 0.05). In young females it appears that training and playing ice hockey might influence BMD and muscle strength in a positive direction. The correlation between BMD and muscle strength seems to weaken with increased exercise level.     

Effects of stretching on peak torque and the H:Q ratio

The purpose of the present study was to examine the acute effects of hamstring and calf stretching on leg extension and flexion peak torque (PT) and the hamstrings-to-quadriceps (H : Q) ratio during maximal, concentric isokinetic muscle actions at 60, 180, and 300 degrees . s (-1) in women. Thirteen women (mean age +/- SD = 20.8 +/- 1.8 yrs; height = 163.0 +/- 5.7 cm; mass = 64.0 +/- 8.3 kg) performed 3 maximal concentric isokinetic leg extension and flexion muscle actions at 3 randomly ordered angular velocities (60, 180, and 300 degrees . s (-1)) before and after a bout of static stretching. The stretching protocol consisted of 1 unassisted and 3 assisted static stretching exercises designed to stretch the posterior muscles of the thigh and leg. Four repetitions of each stretch were held for 30 s with 20 s rest between repetitions. The results indicated that leg flexion PT decreased from pre- to post-stretching (34.9 +/- 3.5 and 32.4 +/- 3.2 Nm, respectively) collapsed across velocity. However, no other changes were observed from pre- to post-stretching for leg extension PT (78.5 +/- 5.9 and 77.8 +/- 5.5 Nm, respectively) and the H : Q ratio (0.47 +/- 0.04 and 0.44 +/- 0.03, respectively). Our findings suggested that despite the stretching-induced decreases in leg flexion PT, leg extension PT and the H : Q ratios were unaltered by the stretching.     

青年男性膝关节等速向心测力研究

目的研究绳肌和股四头肌在不同测试速度下其肌力各指标的变化规律 ,同时为力量素质的评价提供正常值参考。方法利用REV90 0 0等速测力及康复系统对 30名健康男性双侧膝关节的等速向心收缩数据进行测试。结果峰力矩 (PT)及相对峰力矩 (PT/BW )均表现为股四头肌大于绳肌 ,慢速大于快速 ;惯用肢与非惯用肢峰力矩的差异 (Di)在 1 0 %左右 ;到达峰力矩的时间 (TPT)随测试速度增加而显著缩短 ;股四头肌和绳肌峰力矩角 (APT)分别为 50°～ 70°、32°～ 45°。绳肌与股四头肌峰力矩比率 (H/Q)在 50 %～ 60 %之间 ;耐力指数 (WF)在 65%左右。结论此结果为中国航天医学和生理学特别是模拟失重或微重力条件下的肌肉功能评定提供了一个新的思路。     

The effect of a preexercise meal on time to fatigue during prolonged cycling exercise

PURPOSE AND METHODS: Seven subjects exercised to exhaustion on a bicycle ergometer at a workload corresponding to an intensity of 70% maximal oxygen uptake (VO2max). On one occasion (FED), subjects consumed a preexercise carbohydrate (CHO) containing breakfast (100 g CHO) 3 h before exercise. On the other occasion (FASTED), subjects exercised after an overnight fast. Exercise time to fatigue was significantly longer (P < 0.05) when subjects consumed the breakfast (136+/-14 min) compared with when they exercised in the fasted state (109+/-12 min). RESULTS: Pre- and post-exercise muscle glycogen concentrations, respiratory exchange ratio, carbohydrate and fat oxidation, and lactate and insulin concentrations were not significantly different between the two trials. Insulin concentrations decreased significantly (P < 0.05) from 4.7+/-0.05 microIU.mL(-1) to 2.8+/-0.4 microIU.mL(-1) in FED and from 6.6+/-0.6 microIU.mL(-1) to 3.7+/-0.6 microIU.mL(-1) in FASTED subjects and free fatty acid concentrations (FFA) increased significantly (P < 0.05) from 0.09+/-0.02 mmol.L(-1) to 1.4+/-0.6 mmol.L(-1) in FED and from 0.17+/-0.02 mmol.L(-) to 0.74+/-0.27 mmol.L(-1) in FASTED subjects over the duration of the trials. CONCLUSIONS: In conclusion, the important finding of this study is the increased time to fatigue when subjects ingested the CHO meal with no negative effects ascribed to increased insulin concentrations and decreased FFA concentrations after CHO ingestion.     

Concentric quadriceps and hamstrings isokinetic strength in volleyball and soccer players

AIM: Muscular strength is one of the most important components of sport, both for high performance and for injury prevention. One of the most used methods to assess strength muscle balance between dominant (D)/non-dominant (ND) and antagonist/agonist is isokinetic testing. The main purpose of the present study was to describe and to compare isokinetic strength profiles (peak torque, bilateral strength differences between D/ND leg (BD) and hamstrings/quadriceps (H/Q) ratio) in athletes of different sports and positional roles. METHODS: Twenty-eight elite volleyball players and 47 pro soccer players (goalkeepers, n = 5; full-backs, n = 7; defenders, n = 10; midfielders, n = 15; forwards, n = 10) were evaluated using an isokinetic dynamometer (Biodex-System 2). Maximal gravity corrected concentric peak torque of knee extensor and flexor muscles were measured at angular velocities of 360 degrees x s(-1) (6.28 rad x s(-1)) and 90 degrees x s(-1) (1.57 rad x s(-1)). RESULTS: No significant BD were found between soccer and volleyball players with exception of hamstrings at 90 degrees x s(-1) (soccer: 10.6 +/- 8.0% vs volleyball: 6.9 +/- 5.5%). The H/Q ratio was significantly lower in volleyball players at 90 degrees x s(-1) (D: soccer 57.4 +/- 6.7% vs volleyball 50.4 +/- 7.2%; ND: soccer: 56.1 +/- 8.2% vs volleyball: 50.5 +/- 6.4%). No significant differences were found for BD and H/Q ratio in soccer players of different positional roles. CONCLUSION: In general, soccer and volleyball players do not seem to be different concerning BD although a significant difference was observed in hamstrings at 90 degrees x s(-1). Moreover, our data suggest that specific demands of these sports and the different positional roles in soccer did not induce bilateral leg imbalances. However, sport demands seem to influence isokinetic concentric H/Q ratio.     

The effects of proprioceptive or strength training on the neuromuscular function of the ACL reconstructed knee: a randomized clinical trial

OBJECTIVES: The purpose of this study was to determine the effects of a proprioceptive training program (PT) vs. a strength training (ST) program on neuromuscular function after anterior cruciate ligament (ACL) reconstruction. The second purpose was to establish the determinants of functional ability for the operated limb. METHODS: Ten participants with unilateral ACL reconstructions were randomly assigned to one of the following 12-week training protocols: (1) isotonic ST, and (2) PT. The outcome measures were: (1) peak torque time of the hamstring muscles (PeakTT), (2) average concentric and eccentric torques of the quadriceps and hamstring muscles, (3) one-legged single hop for distance (SLHD), (4) one-legged time hop (TH), and (5) subjective scores. RESULTS: : There was a significant group by time interaction effect for PeakTT (P = 0.017). The PT group demonstrated greater percent change in isokinetic torques than the ST group at the end of the 12 weeks (P < or = 0.05). Participants in both groups demonstrated similar significant gains in functional ability and subjective scores (P < or = 0.014). Quadriceps strength is a determinant of functional ability for the operated limb (R2 = 0.72). CONCLUSIONS: : Both training protocols influenced PeakTT. The beneficial effects of ST on PeakTT appear to be load-dependent, while sufficient practice may be crucial in maintaining PeakTT improvements induced by PT. Proprioceptive training alone can induce isokinetic strength gains. Restoring and increasing quadriceps strength is essential to maximize functional ability of the operated knee joint.     

Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement

PURPOSE: This study assessed whether liquid carbohydrate-protein (C+P) supplements, ingested early during recovery, enhance muscle glycogen resynthesis versus isoenergetic liquid carbohydrate (CHO) supplements, given early or an isoenergetic solid meal given later during recovery (PLB). METHODS: Two hours after breakfast (7.0 kcal.kg; 0.3 g.kg P, 1.2 g.kg C, 0.1 g.kg F), six male cyclists performed a 60-min time trial (AMex). Pre- and postexercise, vastus lateralis glycogen concentrations were determined using nMRS. Immediately, 1 h, and 2 h postexercise, participants ingested C+P (4.8 kcal.kg; 0.8 g.kg C, 0.4 g.kg P), CHO (4.8 kcal.kg; 1.2 g.kg C), or PLB (no energy). Four hours postexercise, a solid meal was ingested. At that time, C+P and CHO received a meal identical to breakfast, whereas PLB received 21 kcal.kg (1 g.kg P, 3.6 g.kg C, 0.3 g.kg F); energy intake during 6 h of recovery was identical among treatments. After 6 h of recovery, measurement and cycling protocols (PMex) were repeated. RESULTS: Absolute muscle glycogen utilization was 18% greater (P 相似文献   

Physiological responses to walking with hand weights, wrist weights, and ankle weights

To compare the blood pressure (BP) responses to exercise with 1.36 kg (3.0 lb) hand-held weights (HW), wrist weights (WW), and ankle weights (AW), 12 sedentary males (20.8 +/- 1.2 yr) completed three randomly assigned treadmill exercises at 75% maximum heart rate (HR) reserve. Systolic and diastolic BPs among HW (181.2 +/- 21.9 and 73.2 +/- 7.9 mm Hg), WW (180.1 +/- 27.2 and 71.0 +/- 10.1 mm Hg), and AW (183.8 +/- 26.8 and 71.7 +/- 7.8 mm Hg) were not significantly different (P greater than 0.05). When compared to exercise with no weights (NW), only the diastolic BP for HW was significantly different (+4.4 mm Hg, P less than 0.05). To evaluate the energy cost of exercise with HW, WW, and AW, subjects completed a fourth exercise at constant treadmill speed (6.3 +/- 0.3 km.h-1) and grade (6.3 +/- 1.4%). Oxygen uptake and HR responses were greater (P less than 0.01) for HW (30.4 +/- 0.8 ml.min-1.kg-1; 160.6 +/- 4.0 beats.min-1), WW (30.4 +/- 0.9 ml.min-1.kg-1; 159.7 +/- 4.6 beats.min-1), and AW (29.0 +/- 0.7 ml.min-1.kg-1; 154.6 +/- 4.4 beats.min-1) than for exercise with NW (26.6 +/- 0.7 ml-min-1.kg-1; 147.0 +/- 3.8 beats.min-1). Oxygen uptake and HRs for HW and WW were greater than for AW (P less than 0.05). Ratings of perceived exertion (Borg scale for NW (11.7 +/- 1.8), HW (12.1 +/- 2.0), WW (12.2 +/- 1.8), and AW (12.3 +/- 1.8) were not significantly different (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of aquatic resistance training on neuromuscular performance in healthy women

PURPOSE: The purpose of this study was to investigate the effects of a progressive 10-wk aquatic resistance training on neuromuscular performance and muscle mass of the knee extensors and flexors in healthy women. METHODS: Twenty-four healthy women (34.2 +/- 3.9 yr) were randomly assigned into aquatic exercise (N = 12) and control group (N = 12). Maximum knee extension and flexion torques were measured isometrically and at constant angular velocities of 60 degrees x s(-1) and 180 degrees x s(-1) (isokinetic) with simultaneous electromyography (EMG) recordings of the quadriceps and hamstrings. The lean muscle mass (LCSA) of the quadriceps and hamstring muscles was determined by computed tomography scanning. RESULTS: Significant interaction of group by time was observed in each of the measured parameters. The change in extension and flexion isometric/isokinetic torque varied between 8 and 13% and in EMGs between 10 and 27% in the exercise group. The change in the quadriceps LCSA of the exercise group was 4% and in hamstrings 5.5%. CONCLUSIONS: The results of the present study showed that 10 wk of progressive aquatic resistance training resulted in significant improvement in muscle torque of the knee extensors and flexors accompanied with proportional improvement in neural activation and with significant increase in the LCSA of the trained muscles. Aquatic training can be recommended for neuromuscular conditioning in healthy persons.     

Exercise intensity and erythrocyte 2,3-diphosphoglycerate concentration

The present study examines the acute effects of two different exercise intensities on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Thirty-one females (X +/- SD age = 23.7 +/- 3.37 yr; VO2max = 44.3 +/- 5.40 ml X kg-1 X min-1) completed 2 separate 15-min constant load cycling tests at exercise intensities representing 35 and 75% of VO2max. Venous blood was obtained pre-exercise (PRE), immediately post-exercise (POST), 15 min post-exercise (POST15), and 30 min post-exercise (POST30) to determine lactic acid, 2,3-DPG, and hemoglobin concentrations and hematocrit. Significant increases (P less than 0.01) in lactic acid concentration (1.1 +/- 0.14 at PRE to 6.2 +/- 0.48 m X mol-1 X l-1 at POST), 2,3-DPG concentration (1.9 +/- 0.06 at PRE to 2.1 +/- 0.06 mumol X ml-1 at POST), and 2,3-DPG corrected for plasma volume shift (PVC 2,3-DPG) (1.9 +/- 0.06 at PRE to 2.4 +/- 0.07 mumol X ml-1 at POST15) were observed only following the 75% submaximal exercise. At POST30 (75% VO2max) PVC 2,3-DPG and lactic acid remained 5.3 and 97% (P less than 0.05) above baseline, respectively. An exercise intensity effect was observed only in lactic acid response (P less than 0.05) but not in 2,3-DPG (mumol X ml-1 and mumol X g-1 hemoglobin or PVC 2,3-DPG. A significant time-intensity interaction (P less than 0.05) for PVC 2,3-DPG suggests that PVC 2,3-DPG response over time was different between the two exercise intensity levels, with the 75% intensity eliciting a greater increase in PVC 2,3-DPG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thigh musculature in relation to chronic anterior cruciate ligament tear: muscle size, morphology, and mechanical output before reconstruction

Eighteen male patients who had untreated chronic ACL rupture were studied in order to evaluate thigh muscle size, morphology, and isokinetic performance of the quadriceps muscle. Computed tomography disclosed a 5.1% mean atrophy of the quadriceps (P less than 0.05), 2.1% slight hypertrophy of the hamstrings (P less than 0.05), and also nonsignificant changes of all other muscle areas of the injured thigh. Muscle morphology (m. vastus lateralis) was normal in 11 biopsy specimens, whereas minor abnormalities (irregular shape or hypotrophy) could be seen in the rest. Isokinetic mechanical output of the knee extensors was 71% to 87% of that of the noninjured limb (P less than 0.01), and the mechanical output corrected for differences in quadriceps cross-sectional area was significantly lower in the injured than the uninjured limb. As there were no significant correlations between isokinetic performance and muscle size or qualitative morphology or morphometric data, the strength decrease cannot be explained by muscle atrophy or structural changes per se. We conclude that nonoptimal activation of the muscles during voluntary contractions is probably the most important causative mechanism of the strength decrease found in patients who have chronic symptomatic ACL tear.     

Changes in selected blood measures during repeated days of intense training and carbohydrate control

Ten runners were studied to determine whether selected blood measures were useful indices of the metabolic stress associated with intense training and dietary carbohydrate (CHO) deficiency. The runners performed two diet/training regimens, involving 5 repeated days of intense training approximately 80 min/d, approximately 80% VO2max) and dietary CHO control (8.0 g.kg-1.d-1, EQ-CHO; 3.9 g.kg-1.d-1, LO-CHO). Resting blood samples were obtained after a 3-day control period, after 3 and 5 days of intense training, and after 3 days of rest. Resting uric acid levels were significantly higher (P less than 0.05) after 3 and 5 days of training during the LO-CHO vs EQ-CHO regimen (353 +/- 21 vs 309 +/- 24, and 345 +/- 26 vs 302 +/- 26 mol.l-1, respectively). Resting thyroxine (T4) levels were higher (P less than 0.05) after 5 days of training during the LO-CHO vs EQ-CHO regimen (102.2 +/- 6.2 vs 83.7 +/- 4.5 nmol.l-1, respectively). While creatine kinase levels were elevated after both regimens (P less than 0.05), there was no difference between regimens. Serum cortisol (C) levels were reduced by 10% for both regimens (P less than 0.05), possibly due to an expansion in plasma volume (7.6 and 7.3% for the LO-CHO and EQ-CHO regimens, respectively). Resting FFA levels were increased (P less than 0.05) during both regimens, but there was no difference between the regimens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability.

PURPOSE: Five days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise. METHODS: Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x d(-1) fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)). RESULTS: FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); RER was restored by 1 d CHO and CHO intake during cycling (0.90 +/- 0.01, 0.80 +/- 0.01, 0.91 +/- 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 +/- 0.01, 0.88 +/- 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 +/- 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 +/- 4 g vs 45 +/- 3 g, P < 0.05), whereas CHO oxidation was reduced (354 +/- 11 g vs 419 +/- 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 +/- 0.67 min vs 25.45 +/- 0.96 min, NS). CONCLUSION: Adaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting approximately 25 min undertaken after 2 h of submaximal cycling.