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Ongoing climate change threatens the biodiversity of glacier-fed river ecosystems worldwide through shifts in water availability and timing, temperature, chemistry, and channel stability. However, tropical glacier-fed rivers have received little attention compared to those in temperate and Arctic biomes, despite their unique biodiversity potentially responding differently due to additional stress from higher altitude locations thus lower oxygen availability, diurnal freeze-thaw cycles, and annual monsoon rainfall disturbances. However, tropical glacier-fed rivers have received little attention compared to those in temperate and Arctic biomes, despite their unique biodiversity potentially responding differently due to additional stress from higher altitude locations thus lower oxygen availability, diurnal freeze-thaw cycles, and annual monsoon rainfall disturbances. This study quantified aquatic biodiversity responses to decreasing glacier cover in the Cordillera Blanca range of the Peruvian Andes. Ten rivers were studied along a gradient of decreasing glacier cover in the Parón, Huaytapallana, and Llanganuco basins, with a specific focus on macroinvertebrates and physicochemical parameters in both the dry and wet seasons. We found higher temperatures, more stable and lower turbidity rivers as glacier cover decreased, which were related significantly to higher local diversity and lower ß-diversity. Analysis of similarity revealed significant differences in the macroinvertebrate community among rivers with high, medium, or low glacier cover, illustrating turnover from specialists to generalists as glacial influence decreased. Redundancy analysis demonstrated that there were more species found to prefer stable beds and water temperatures in medium and low glacier cover in a catchment rivers. However, certain taxa in groups such as Paraheptagyia, Orthocladiinae, Anomalocosmoecus, and Limonia may be adapted to high glacial influence habitats and at risk of glacier retreat. Although species composition was different to other biomes, the Cordillera Blanca rivers showed similar benthic macroinvertebrate biodiversity responses to glacier retreat, supporting the hypothesis that climate change will have predictable effects on aquatic biodiversity in mountain ranges worldwide.
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Biodiversidad , Cubierta de Hielo , Invertebrados , Ríos , Animales , Invertebrados/fisiología , Cambio Climático , Estaciones del Año , TemperaturaRESUMEN
BACKGROUND: Many studies have investigated isokinetic performance in volleyball players but not through surface maps. OBJECTIVES: The goals of this study were to assess velocity-specific isokinetic knee extensor-flexor muscle strength and to compare the isokinetic knee extensor-flexor muscles between professional (PRO) and under-17 (U17) female volleyball players. METHOD: This cross-sectional laboratory study was developed with two groups: PRO (n = 12), medianage = 21.3 years, and U17 (n = 9), medianage = 15 years. Peak torque, total work, mean power, angle of peak torque, hamstring-quadriceps torque ratio (H-Q ratio) and torque-angle-velocity surface maps were analysed from knee extension-flexion at 60, 120 and 300 degrees per second (°/s). RESULTS: Significant differences were identified for extensor peak torque between PRO x = 202.3 Newton metre (N·m) (standard deviation [SD] = 24.4) and U17 x = 141.6 N·m (30.1) at 60 °/s (p < 0.001; d = 2.21) as well as flexor peak torque (PRO x = 75.7 N·m [10.3] and U17 x = 57.7 N·m [11.4]) at 120 °/s (p < 0.001; d = 1.65) for the dominant limb. There were also significant group differences for total work and mean power at all velocities for extension and flexion. Surface maps demonstrated higher torque at lower speeds for both groups with smaller torque changes across velocities for flexion. CONCLUSION: Different groups of female volleyball players showed contrasting concentric knee muscle strength across isokinetic velocities. CLINICAL IMPLICATIONS: These results demonstrate the importance of specific strength training for different age groups, even within the same sport, and provide insight into muscle strength.
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Strength training (ST) is known to promote muscle hypertrophy and body composition adaptations. However, only a few studies investigated the effects of ST combined with antioxidant supplementation (AS) on these adaptations. The aim of this study was to investigate chronic effects of ST combined with AS on fat mass (FM) and fat-free mass (FFM) of young women. In a double-blinded design, thirty-three subjects (22.9 ± 2.5 years, 57.7 ± 8.4 kg, 1.6 ± 0.6 m) were allocated into three groups: 1) vitamins (n=12), 2) placebo (n=11) and 3) control (n=10). Vitamins and placebo underwent a ST program for 10 weeks. Vitamins supplemented with vitamin C (1g/day) and E (400IU/day) during the training period. FM and FFM were assessed by DEXA. Multiple 3 x 2 (group x time) mixed-factor ANOVA with Tukey adjustment was performed to examine differences in the dependent variables. The significance level was set at P ≤ .05. Only placebo increased total FFM (34.9 ± 4.9 vs 36.3 ± 4.8 kg, P<0.05) and decreased total FM (21.8 ± 7.8 vs 21.0 ± 8.3 kg, P<0.05) after training for 10 weeks. Moreover, only placebo presented a significantly greater FFM percent change from pre to post-intervention compared to control (4.0 ± 3.4 vs -0.7 ± 3.1%, respectively, P < 0.05). These results suggest that chronic AS can mitigate ST related improvements of body composition in young women.
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BACKGROUND: and Purpose: Knee muscle strength deficits have been reported in individuals who have undergone anterior cruciate ligament reconstruction (ACLR). Isokinetic testing is a valid way to assess muscle strength. Some isokinetic variables, including the range of motion in the phases to attain a specific velocity, load range (sustained specific velocity), time to achieve deceleration, and qualitative analysis of the torque-angle velocity relationship, may contribute to understanding recovery of these individuals after surgery. Thus, the purpose of this study was to compare the load range (LR), time to attain velocity (TTAV), deceleration time (DT) phases, total range of motion (ROM), peak torque/body mass (PT/BM), angle of peak torque (AngPT) during LR and torque-angle-velocity relationships (TAV3D) between post ACLR and matched control subjects.Study design: Case-control. METHODS: Seven men who underwent ACLR and seven matched controls were evaluated from four to six months after surgery. Testing was performed on a Biodex System 4 isokinetic dynamometer in concentric mode at 60, 120 and 300 °/s, for knee flexion and extension. RESULTS: Statistically significant differences were seen for extension ROM at 60 °/s where ROM was greater in the control group. PT/BM for extensors was also significantly greater in controls by 20 % compared to ACLR at 60 and 120 °/s. PT/BM for flexors was significantly greater for controls at 60 °/s (â¼15 %). TAV3D showed differences in torque and, specifically, the control group sustained knee flexion torque for a greater range of motion when compared to the ACLR group. CONCLUSION: The ACL group presented with lower ROM and PT/BM, therefore exhibiting worse muscle performance in comparison to the control group.Level of Evidence: 3.
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BACKGROUND: Kinesiology Tape (KT) is widely used in sports rehabilitation and by those performing physical activity, however, there is no consensus in the scientific literature about its effectiveness on performance, strength or muscle activation.Purpose: The purpose of this study was to measure the acute effects of KT in static rest, and during knee extension maximal voluntary isometric contraction (MVIC) performance in resistance trained men.Study Design: Observational, descriptive, comparative. METHODS: Eighteen young, healthy, trained males (age: 25 ± 6 years, height: 176.0 ± 5 cm, and mass: 81.8 ± 8.0 kg) volunteered to participate. Initially, they were in a relaxed sitting position of 90 degrees knee flexion with their limb supported by the machine lever arm to measure passive tension of the tissues of the knee joint. Then, they performed three MVIC trials of five seconds each with a three-minute rest between trials, in four randomized experimental conditions, with 10-min rest between conditions: (a) control, no taping; (b) Knee Sleeve; (c) KT; and (d) sham. During all MVICs, peak force, impulse, and muscle activation of the vastus lateralis (integrated electromyography [IEMG] and median frequency) were measured. RESULTS: Repeated measures ANOVAs revealed no statistical differences between conditions for passive tension (p > 0.05), peak force (p > 0.05), impulse (p > 0.05), IEMG (p > 0.05), or median frequency (p > 0.05). CONCLUSION: KT does not influence passive tension during static position at 90 degrees of knee flexion. KT does not affect quadriceps activation or force production during a maximal voluntary isometric contraction in the same position. LEVEL OF EVIDENCE: 3a.
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This was a placebo-controlled randomized study that aimed to investigate the effects of strength training (ST) combined with antioxidant supplementation on muscle performance and thickness. Forty-two women (age, 23.8 ± 2.7 years; body mass, 58.7 ± 11.0 kg; height, 1.63 ± 0.1 m) were allocated into 3 groups: vitamins (n = 15), placebo (n = 12), or control (n = 15). The vitamins and placebo groups underwent an ST program, twice a week, for 10 weeks. The vitamins group was supplemented with vitamins C (1 g/day) and E (400 IU/day) during the ST period. Before and after training, peak torque (PT) and total work (TW) were measured on an isokinetic dynamometer, and quadriceps muscle thickness (MT) was assessed by ultrasound. Mixed-factor ANOVA was used to analyze data and showed a significant group × time interaction for PT and TW. Both the vitamins (37.2 ± 5.4 to 40.3 ± 5.6 mm) and placebo (39.7 ± 5.2 to 42.5 ± 5.6 mm) groups increased MT after the intervention (P < 0.05) with no difference between them. The vitamins (146.0 ± 29.1 to 170.1 ± 30.3 N·m) and placebo (158.9 ± 22.4 to 182.7 ± 23.2 N·m) groups increased PT after training (P < 0.05) and PT was higher in the placebo compared with the control group (P = 0.01). The vitamins (2068.3 ± 401.2 to 2295.5 ± 426.8 J) and placebo (2165.1 ± 369.5 to 2480.8 ± 241.3 J) groups increased TW after training (P < 0.05) and TW was higher in the placebo compared with the control group (P = 0.01). Thus, chronic antioxidant supplementation may attenuate peak torque and total work improvement in young women after 10 weeks of ST.
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Antioxidantes/administración & dosificación , Ácido Ascórbico/administración & dosificación , Suplementos Dietéticos , Contracción Muscular/efectos de los fármacos , Fuerza Muscular/efectos de los fármacos , Músculo Esquelético/efectos de los fármacos , Entrenamiento de Fuerza , Vitamina A/administración & dosificación , Adulto , Antioxidantes/efectos adversos , Ácido Ascórbico/efectos adversos , Fenómenos Biomecánicos , Brasil , Suplementos Dietéticos/efectos adversos , Método Doble Ciego , Femenino , Humanos , Hipertrofia , Músculo Esquelético/diagnóstico por imagen , Factores de Tiempo , Torque , Resultado del Tratamiento , Ultrasonografía , Vitamina A/efectos adversos , Adulto JovenRESUMEN
Ruas, CV, Brown, LE, Lima, CD, Costa, PB, and Pinto, RS. Effect of three different muscle action training protocols on knee strength ratios and performance. J Strength Cond Res 32(8): 2154-2165, 2018-Hamstring to quadriceps (H:Q) ratios are often used to assess strength imbalances. The aims of this study were to compare 3 different muscle action training protocols on H:Q strength balance and functional performance. Forty untrained men (age: 22.87 ± 2.28 years, mass: 70.66 ± 11.049 kg, ht: 174.29 ± 6.90 cm) performed 6 weeks of training on an isokinetic dynamometer. They were randomly assigned to one of 4 groups; concentric quadriceps and concentric hamstring (CON/CON), eccentric quadriceps and eccentric hamstring (ECC/ECC), concentric quadriceps and eccentric hamstring (CON/ECC), or no training. Mixed Factor analyses of variance were used to compare interactions for variables pretest and posttest between groups (p ≤ 0.05). The ECC/ECC group showed significant increases in H:Q functional ratio (pre = 0.73 ± 0.092, post = 0.87 ± 0.098), ECC peak torque (PT) (pre = 226.44 ± 67.80 N·m, post = 331.74 ± 54.44 N·m), isometric PT (IPT) (pre = 173.69 ± 41.41 N·m, post = 203.091 ± 30.82 N·m), countermovement jump (CMJ) (pre = 52.73 ± 6.95 cm, post = 58.16 ± 6.10 cm), and drop jump (DJ) (pre = 52.91 ± 6.080 cm, post = 58.20 ± 7.72 cm), whereas the CON/CON group increased the rate of torque development (pre = 152.19 ± 65.0074 N·m·s, post = 225.26 ± 88.80 N·m·s). There were no differences between groups for CON PT, squat jump, conventional ratio or 40 m sprint. Our findings suggest that ECC/ECC training may be the most effective at increasing functional H:Q strength ratios, as well as ECC PT, IPT, CMJ, and DJ performance. Eccentric training increases ECC PT, thereby increasing the functional H:Q ratio. Eccentric training also improves vertical jumping involving ECC actions. CON/CON training may be more effective at increasing explosive muscle strength.
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Músculos Isquiosurales/fisiología , Articulación de la Rodilla/fisiología , Fuerza Muscular/fisiología , Músculo Cuádriceps/fisiología , Adulto , Humanos , Masculino , Torque , Adulto JovenRESUMEN
OBJECTIVE: To evaluate the time course of peak torque and total work recovery after a resistance training session involving the bench press exercise. DESIGN: Repeated measures with a within subject design. METHODS: Twenty-six resistance-trained men (age: 23.7±3.7years; height: 176.0±5.7cm; mass: 79.65±7.61kg) performed one session involving eight sets of the bench press exercise performed to momentary muscle failure with 2-min rest between sets. Shoulder horizontal adductors peak torque (PT), total work (TW), delayed onset muscle soreness (DOMS) and subjective physical fitness were measured pre, immediately post, 24, 48, 72 and 96h following exercise. RESULTS: The exercise protocol resulted in significant pectoralis major DOMS that lasted for 72h. Immediately after exercise, the reduction in shoulder horizontal adductors TW (25%) was greater than PT (17%). TW, as a percentage of baseline values, was also less than PT at 24, 48 and 96h after exercise. Additionally, PT returned to baseline at 96h, while TW did not. CONCLUSIONS: Resistance trained men presented dissimilar PT and TW recovery following free weight bench press exercise. This indicates that recovery of maximal voluntary contraction does not reflect the capability to perform multiple contractions. Strength and conditioning professionals should be cautious when evaluating muscle recovery by peak torque, since it can lead to the repetition of a training session sooner than recommended.
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Músculo Esquelético/fisiología , Aptitud Física/fisiología , Recuperación de la Función , Entrenamiento de Fuerza , Humanos , Masculino , Fatiga Muscular/fisiología , Fuerza Muscular/fisiología , Mialgia/fisiopatología , Aptitud Física/psicología , Recuperación de la Función/fisiología , Entrenamiento de Fuerza/métodos , Hombro/fisiología , Factores de Tiempo , Adulto JovenRESUMEN
OBJECTIVES: The purpose of the present study was to examine knee extensor and flexor muscle strength ratios of an elite group of diving athletes. METHODS: Sixteen divers (10 females and 6 males) from the Brazil national team were assessed for lower-body strength. They had participated in international competitions such as the 2016 Olympic Games and 2015 Pan American Games. The dynamic concentric torque of their knee flexor and extensor muscles were evaluated using a Biodex isokinetic dynamometer. Bilateral tests were performed at 60º s-1. Flexor to extensor (F/E) peak torque ratio and percentage bilateral difference (BD%) was also measured. RESULTS: The results revealed that elite diving athletes produced higher than usual reported in previous studies for relative knee extension torque (3.2 for females and 3.6 for males Nâmâkg-1). However, they presented low levels of knee flexor torque (1.5 for females and 1.8 for males Nâmâkg-1). These results are reflected in a low F/E ratio (0.39 to 0.49). Males presented a greater BD% in knee flexors when compared to females (12.4% vs 6.6%). CONCLUSION: Elite diving athletes demonstrated high knee extensor and low knee flexor strength. This partially explains their low F/E ratio, which might increase risk of knee injuries. Strength and conditioning programs should strive to correct knee strength imbalances in diving athletes where necessary.
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Buceo/fisiología , Articulación de la Rodilla/fisiología , Rodilla/fisiología , Fuerza Muscular , Músculo Esquelético/fisiología , Torque , Adolescente , Adulto , Atletas , Traumatismos en Atletas/etiología , Traumatismos en Atletas/prevención & control , Brasil , Femenino , Humanos , Traumatismos de la Rodilla/etiología , Traumatismos de la Rodilla/prevención & control , Extremidad Inferior , Masculino , Adulto JovenRESUMEN
The purpose of this study was to measure the acute effects of pre-exhaustion vs. traditional exercise order on neuromuscular performance and sEMG in trained men. Fourteen young, healthy, resistance trained men (age: 25.5 ± 4.0 years, height: 174.9 ± 4.1 cm, and total body mass: 80.0 ± 11.1 kg) took part of this study. All tests were randomized and counterbalanced for all subjects and experimental conditions. Volunteers attended one session in the laboratory. First, they performed ten repetition maximum (10RM) tests for each exercise (bench press and triceps pushdown) separately. Secondly, they performed all three conditions at 10RM: pre-test (bench press and triceps pushdown, separately), pre-exhaustion (triceps pushdown+bench press, PE) and traditional (bench press+triceps pushdown, TR), and rested 30 minutes between conditions. Results showed that pre-test was significantly greater than PE (p = 0.031) but not different than TR, for total volume load lifted. There was a significant difference between the pre-test and the time-course of lactate measures (p = 0.07). For bench press muscle activity of the pectoralis major, the last repetition was significantly greater than the first repetition (pre-test: p = 0.006, PE: p = 0.016, and TR: p = 0.005). Also, for muscle activity of the triceps brachii, the last repetition was significantly greater than the first repetition (pre-test: p = 0.001, PE: p = 0.005, and TR: p = 0.006). For triceps pushdown, muscle activity of the triceps brachii, the last repetition was significantly greater than the first repetition (pre-test: p = 0.006, PE: p = 0.016, and TR: p = 0.005). For RPE, there were no significant differences between PE and TR (p = 0.15). Our results suggest that exercise order decreases repetitions performed, however, neuromuscular fatigue, lactate, and RPE are not impacted. The lack of difference in total volume load lifted between PE and TR might explain, at least in part, the similar metabolic and perceptual responses. Key pointsThe effects of different exercise order schemes (e.g. PE and TR) on muscle activity and strength performance indicated that similar responses were observed when comparing these schemes.Strength and conditioning coaches should consider these results when prescribing resistance training programs.The primary target (e.g. muscle group) of the training session should trained first, when fatigue level low, in order to maximize training outcomes.
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Whole-body cryotherapy (WBC) has been used as a recovery strategy following different sports activities. Thus, the aim of the study reported here was to examine the effect of WBC on vertical jump recovery following a high-intensity exercise (HIE) bout. Twelve trained men (mean ± standard deviation age = 23.9±5.9 years) were randomly exposed to two different conditions separated by 7 days: 1) WBC (3 minutes of WBC at -110°C immediately after the HIE) and 2) control (CON; no WBC after the HIE). The HIE consisted of six sets of ten repetitions of knee extensions at 60° · s(-1) concentric and 180° · s(-1) eccentric on an isokinetic dynamometer. The vertical jump test was used to evaluate the influence of HIE on lower extremity muscular performance. The vertical jump was performed on a force platform before HIE (T1) and 30 minutes after (T2) the WBC and CON conditions. As a result of HIE, jump height, muscle power, and maximal velocity (Vmax) had significant decreases between T1 and T2, however no significance was found between the WBC and CON conditions. The results indicate that one session of WBC had no effect on vertical jump following an HIE compared with a CON condition. WBC may not improve muscle-function (dependent on stretch-shortening cycle) recovery in very short periods (ie, 30 minutes) following HIE.
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This study compared the time course of elbow flexor muscle recovery after multi- and single-joint exercises in highly resistance-trained men. Sixteen men (24.5 ± 5.5 years) performed, in a counterbalanced order, 8 sets of 10 repetition maximum (RM) unilateral seated row exercise and 8 sets of 10RM unilateral biceps preacher curl exercise using the contralateral arm. Maximum isometric peak torque (PT) and delayed onset muscle soreness (DOMS) were recorded at baseline (pre), 10 minutes, 24, 48, 72, and 96 hours after each exercise protocol. There was a significant decrease (p ≤ 0.05) in elbow flexor PT 10 minutes after both the multi- and single-joint exercise sessions. However, PT decrease was greater after single-joint (26.8%) when compared with multi-joint (15.1%) exercise (p ≤ 0.05). In addition, elbow flexor PT was lower (8.4%) than baseline 24 hours after the single-joint exercise (p < 0.01), whereas PT returned to baseline 24 hours after the multi-joint exercise. Compared with baseline, DOMS increased at 24, 48, and 72 hours after single-joint exercise (p ≤ 0.05). However, DOMS returned to baseline levels after 72 hours after multi-joint exercise. In addition, DOMS after single-joint exercise was greater (p ≤ 0.05) than after multi-joint exercise at 24, 48, and 72 hours after exercise. Our data suggest that after a resistance training session, highly resistance-trained men experience dissimilar elbow flexor strength recovery between single-joint and multi-joint exercises. Likewise, elbow flexor DOMS is greater and takes longer to recover after single-joint exercise.
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Músculo Esquelético/lesiones , Recuperación de la Función/fisiología , Entrenamiento de Fuerza/métodos , Adulto , Humanos , Articulaciones/fisiología , Masculino , Fuerza Muscular/fisiología , Mialgia/fisiopatología , Factores de Tiempo , Adulto JovenRESUMEN
The purposes of this study were to measure the acute effects of knee wraps (KWs) on knee and hip joint kinematics, dynamic muscle activation from the vastus lateralis (VL) and gluteus maximus (GM), and rating of perceived exertion (RPE) during the back squat exercise at 2 different intensities. Fourteen resistance-trained men (age: 24 ± 4 years, height: 176 ± 6 cm, body mass: 81 ± 11 kg, back squat 1 repetition maximum [1RM]: 107 ± 30 kg, 3 ± 1 year of back squat experience) performed 1 set of 3 repetitions under 4 different conditions, to a depth of approximately 90 degrees of knee joint flexion, and in random order: KWs at 60% 1RM (KW60), KWs at 90% 1RM (KW90), without knee wraps (NWs) at 60% 1RM (NW60), and NWs at 90% 1RM (NW90). The dependent variables obtained were vertical and horizontal bar displacement, peak joint angle in the sagittal plane (hip and knee joints), concentric and eccentric muscle activation (by integrated electromyography) from the VL and GM, and RPE. For muscle activity, there were significant decreases in the VL NWs at 60% 1RM (p = 0.013) and a significant increase NWs at 90% 1RM (p = 0.037). There was a significant increase in VL muscle activity at 90% 1RM, when compared with 60% 1RM (KW: p = 0.001, effect size (ES) = 1.51 and NW: p < 00.001, ES = 1.67). There was a decrease in GM muscle activity NWs only at 60% 1RM (p = 0.014). There was a significant increase in GM muscle activity at 90% 1RM, when compared with 60% 1RM (KW: p < 0.001 and NW: p < 0.001). For peak hip joint flexion angle, there was significant decreases between intensities (90% 1RM < 60% 1RM) only to NWs condition (p = 0.009), and there was greater knee flexion NWs for both intensities: 60% 1RM (p < 0.001) and 90% 1RM (p = 0.018). For normalized vertical barbell displacement, there were significant differences between intensities when using KWs (p = 0.022). There were significant differences in RPE between 60 and 90% 1RM for each condition: KWs (p < 0.001) and NWs (p < 0.001). In conclusion, the use of KWs results in decreased muscle activation of the VL at the same intensity (90% 1RM).
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Vendajes de Compresión , Articulación de la Cadera/fisiología , Articulación de la Rodilla/fisiología , Músculo Esquelético/fisiología , Esfuerzo Físico/fisiología , Entrenamiento de Fuerza , Adulto , Fenómenos Biomecánicos , Electromiografía , Humanos , Masculino , Músculo Cuádriceps/fisiología , Distribución Aleatoria , Adulto JovenRESUMEN
The aging process causes many changes in muscle strength, and analysis of explosive force from handgrip strength seems to be useful and promising in studying the aging musculoskeletal system. Therefore, the purpose of this study was to investigate if explosive force parameters [rate of force development (RFD) and contractile impulse (CI) over the time interval of 0-200 ms from the onset of contraction] during handgrip efforts decline differently than maximum handgrip strength with increasing age. Twenty healthy young women (20-27 years) and 65 healthy elderly women, assigned into three age groups (50-64, 65-74, and 75-86 years), participated in this study. All participants performed two maximal grip attempts. Handgrip data were recorded as force-time curves, peak force, and explosive force parameters. Our results revealed that peak force decreased significantly (p < 0.05) for those who are 65 years old, while explosive force parameters decreased significantly (p < 0.05) for those aged 50 years. These data indicate that the decline in explosive grip force-generating capacity may begin earlier (i.e., for those aged 50 years old) than peak force during the aging process. Our findings suggest that the aging process reduces the explosive grip force-generating capacity before affecting peak force.
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Envejecimiento/fisiología , Metabolismo Energético , Fuerza de la Mano/fisiología , Contracción Isométrica/fisiología , Músculo Esquelético/fisiología , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Voluntarios Sanos , Humanos , Persona de Mediana Edad , Adulto JovenRESUMEN
It is previously demonstrated that static stretching was associated with a decrease in running economy and distance run during a 30-minute time trial in trained runners. Recently, the detrimental effects of static stretching on economy were found to be limited to the first few minutes of an endurance bout. However, economy remains to be studied for its direct effects on performance during shorter endurance events. The aim of this study was to investigate the effects of static stretching on 1-mile uphill run performance, electromyography (EMG), ground contact time (GCT), and flexibility. Ten trained male distance runners aged 24 ± 5 years with an average VO2max of 64.9 ± 6.5 mL·kg-1·min-1 were recruited. Subjects reported to the laboratory on 3 separate days interspersed by 72 hours. On day 1, anthropometrics and V[Combining Dot Above]O2max were determined on a motor-driven treadmill. On days 2 and 3, subjects performed a 5-minute treadmill warm-up and either performed a series of 6 lower-body stretches for three 30-second repetitions or sat still for 10 minutes. Time to complete a 1-mile run under stretching and nonstretching conditions took place in randomized order. For the performance run, subjects were instructed to run as fast as possible at a set incline of 5% until a distance of 1 mile was completed. Flexibility from the sit and reach test, EMG, GCT, and performance, determined by time to complete the 1-mile run, were recorded after each condition. Time to complete the run was significantly less (6:51 ± 0:28 minutes) in the nonstretching condition as compared with the stretching condition (7:04 ± 0:32 minutes). A significant condition-by-time interaction for muscle activation existed, with no change in the nonstretching condition (pre 91.3 ± 11.6 mV to post 92.2 ± 12.9 mV) but increased in the stretching condition (pre 91.0 ± 11.6 mV to post 105.3 ± 12.9 mV). A significant condition-by-time interaction for GCT was also present, with no changes in the nonstretching condition (pre 211.4 ± 20.8 ms to post 212.5 ± 21.7 ms) but increased in the stretching trial (pre 210.7 ± 19.6 ms to post 237.21 ± 22.4 ms). A significant condition-by-time interaction for flexibility was found, which was increased in the stretching condition (pre 33.1 ± 2 to post 38.8 ± 2) but unchanged in the nonstretching condition (pre 33.5 ± 2 to post 35.2 ± 2). Study findings indicate that static stretching decreases performance in short endurance bouts (â¼8%) while increasing GCT and muscle activation. Coaches and athletes may be at risk for decreased performance after a static stretching bout. Therefore, static stretching should be avoided before a short endurance bout.
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Rendimiento Atlético/fisiología , Ejercicios de Estiramiento Muscular/efectos adversos , Músculo Esquelético/fisiopatología , Carrera/fisiología , Ejercicio de Calentamiento/fisiología , Adulto , Estudios Cruzados , Electromiografía , Prueba de Esfuerzo , Humanos , Masculino , Factores de Tiempo , Adulto JovenRESUMEN
PURPOSE: Preload of antagonist muscles can be achieved by reciprocal actions (RAs) or by opposing muscle actions. However, evidence concerning neuromuscular and fatigue responses are scarce. OBJECTIVE: To compare the effects of different knee flexor (KF) preload methods on knee extension (KE) vastus medialis muscle fatigue, based on EMG-spectral index (FI), load range (LR), total work (TW), blood lactate (LAC) and biceps femoris co-activation (BFc) during resistance exercise. METHODS: Twenty-four healthy men (23.5±3.6yrs) performed three antagonist pre-load isokinetic exercises (4 sets, 10 repetitions, 60°s(-1), 1min rest between sets): RA (KF contraction immediately followed by KE); Superset (SS; one KF set immediately followed by one KE set); Multiple Set (MS; four KF sets followed by four KE sets). RESULTS: Total work was significantly greater in RA. There was no significant decrease in LR between sets in RA. The BFc did not differ between protocols (p=0.063). However, RA presented greater biceps femoriscoactivation. The FI was greater during SS compared to RA and MS (p<0.05). The SS had greater LAC when compared to MS and RA (p=0.005 and p=0.007, respectively). CONCLUSION: It is suggested that the RA protocol is more neuromuscular and metabolic efficient during the performance of knee extension resistance exercise.
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Ácido Láctico/sangre , Contracción Muscular/fisiología , Fatiga Muscular/fisiología , Músculo Esquelético/fisiología , Esfuerzo Físico/fisiología , Equilibrio Postural/fisiología , Entrenamiento de Fuerza/métodos , Adaptación Fisiológica/fisiología , Adulto , Humanos , Masculino , Fuerza Muscular/fisiologíaRESUMEN
The aim of this study was to compare the effects of low- and high-volume strength training on strength, muscle activation and muscle thickness (MT) of the lower- and upper-body, and on muscle quality (MQ) of the lower-body in older women. Twenty apparently healthy elderly women were randomly assigned into two groups: low-volume (LV, n=11) and high-volume (HV, n=9). The LV group performed one-set of each exercise, while the HV group performed three-sets of each exercise, twice weekly for 13 weeks. MQ was measured by echo intensity obtained by ultrasonography (MQEI), strength per unit of muscle mass (MQST), and strength per unit of muscle mass adjusted with an allometric scale (MQAS). Following training, there was a significant increase (p≤0.001) in knee extension 1-RM (31.8±20.5% for LV and 38.3±7.3% for HV) and in elbow flexion 1-RM (25.1±9.5% for LV and 26.6±8.9% for HV) and in isometric maximal strength of the lower-body (p≤0.05) and upper-body (p≤0.001), with no difference between groups. The maximal electromyographic activation for both groups increased significantly (p≤0.05) in the vastus medialis and biceps brachii, with no difference between groups. All MT measurements of the lower- and upper-body increased similarly in both groups (p≤0.001). Similar improvements were also observed in MQEI (p≤0.01), MQST, and MQAS (p≤0.001) for both groups. These results demonstrate that low- and high-volume strength training promote similar increases in neuromuscular adaptations of the lower- and upper-body, and in MQ of the lower-body in elderly women.
Asunto(s)
Envejecimiento/fisiología , Fuerza Muscular/fisiología , Músculo Esquelético/fisiología , Esfuerzo Físico/fisiología , Entrenamiento de Fuerza/métodos , Adaptación Fisiológica/fisiología , Anciano , Articulación del Codo/fisiología , Electromiografía , Femenino , Humanos , Articulación de la Rodilla/fisiología , Persona de Mediana Edad , Músculo Esquelético/diagnóstico por imagen , Rango del Movimiento Articular/fisiología , UltrasonografíaRESUMEN
The purpose of this investigation was to compare partial range-of-motion vs. full range-of-motion upper-body resistance training on strength and muscle thickness (MT) in young men. Volunteers were randomly assigned to 3 groups: (a) full range of motion (FULL; n = 15), (b) partial range of motion (PART; n = 15), or (c) control (CON; n = 10). The subjects trained 2 d · wk(-1) for 10 weeks in a periodized program. Primary outcome measures included elbow flexion maximal strength measured by 1 repetition maximum (1RM) and elbow flexors MT measured by ultrasound. The results indicated that elbow flexion 1RM significantly increased (p < 0.05) for the FULL (25.7 ± 9.6%) and PART groups (16.0 ± 6.7%) but not for the CON group (1.7 ± 5.5%). Also, FULL 1RM strength was significantly greater than the PART 1RM after the training period. Average elbow flexor MT significantly increased for both training groups (9.65 ± 4.4% for FULL and 7.83 ± 4.9 for PART). These data suggest that muscle strength and MT can be improved with both FULL and PART resistance training, but FULL may lead to greater strength gains.
Asunto(s)
Fuerza Muscular/fisiología , Músculo Esquelético/anatomía & histología , Rango del Movimiento Articular/fisiología , Entrenamiento de Fuerza , Adolescente , Adulto , Codo/diagnóstico por imagen , Codo/fisiología , Humanos , Masculino , Músculo Esquelético/fisiología , Tamaño de los Órganos , Ultrasonografía , Adulto JovenRESUMEN
The purpose of this study was to compare the effect of different rest intervals and contraction velocities on muscle recovery following resistance exercise. 18 children (11.1 ± 0.52 yrs) and 19 adolescents (15.8 ± 0.49 yrs) performed three sets of 10 isokinetic repetitions at 60°/s and 180°/s. The work-to-rest ratio (W/R) was 1:2 and 1:4 for 60°/s, and 1:6 and 1:12 for 180°/s. ANOVA revealed that children demonstrated no significant decline in PT from the first to third set with any rest interval, but there was a significant (p < .05) decline for adolescents when a W/R of 1:2, 1:4 and 1:6 were used. Adolescents demonstrated significantly greater blood lactate (BLa) concentrations than children after three sets of resistance exercise. The present study indicates that adolescents may require longer rest intervals to recover full PT when compared with children.
Asunto(s)
Articulación de la Rodilla/fisiología , Fatiga Muscular/fisiología , Músculo Esquelético/metabolismo , Entrenamiento de Fuerza/métodos , Descanso/fisiología , Adaptación Fisiológica/fisiología , Adolescente , Factores de Edad , Análisis de Varianza , Niño , Humanos , Ácido Láctico/sangre , Masculino , Contracción Muscular/fisiología , Dinamómetro de Fuerza Muscular , Músculo Esquelético/fisiología , Factores de Tiempo , TorqueRESUMEN
Comparisons between men and women of time course responses of strength, delayed-onset muscle soreness (DOMS), and muscle swelling after a resistance training session are still controversial. Therefore, this study examined gender differences in strength loss, muscle thickness (MT), and DOMS between young men and women. Thirty apparently healthy, untrained volunteers (14 women and 16 men) participated in the study protocol. The resistance exercise session consisted of 8 sets at 10 repetition maximum load of the elbow flexor muscles of their dominant arm. Maximum isokinetic peak torque (PT), MT, and DOMS were recorded at baseline (TB), immediately after exercise (T0), and at 1 (T1), 2 (T2), 3 (T3), and 4 (T4) days after exercise. Baseline strength was expressed as 100%. There were no significant differences between the sexes for relative PT loss immediately after exercise (T0 = 74.31 ± 8.26% for men and 76.00 ± 6.31% for women). Also, PT was still significantly less than baseline from T1 to T4 for both genders. In contrast, recovery from PT was longer in women when compared with that in men. Muscle thickness responded similarly to PT in both genders. However, there was no significant difference between genders for DOMS at any time point. The time point that showed the greatest degree of mean soreness was T2 (4.94 ± 2.38 mm for men and 4.45 ± 2.07 mm for women). Our data suggest that after resistance exercise, women and men experience similar immediate strength loss; however they have dissimilar strength recovery across 4 days of recovery. Likewise, both genders experience a different time course of MT response after a traditional resistance exercise protocol. In contrast, men and women develop and dissipate muscle soreness in a similar manner.