Electromyographic analysis of hip adductor muscles in soccer instep and side-foot kicking

ABSTRACT

A possible link between soccer-specific injuries, such as groin pain and the action of hip adductor muscles has been suggested. This study aimed to investigate neuromuscular activation of the adductor magnus (AM) and longus (AL) muscles during instep and side-foot soccer kicks. Eight university soccer players performed the two types of kick at 50%, 75% and 100% of the maximal ball speed. Surface electromyography (EMG) was recorded from the AM, AL, vastus lateralis (VL) and biceps femoris (BF) muscles of both kicking and supporting legs and the kicking motions were three-dimensionally captured. In the kicking leg, an increase in surface EMG with an increase in ball speed during instep kicking was noted in the AM muscle (p < 0.016), but not in AL, VL or BF muscles (p > 0.016). In the supporting leg, surface EMG of both AM and AL muscles was significantly increased with an increase in the ball speed before ball impact during both instep and side-foot kicks (p < 0.016). These results suggest that hip adductor muscles markedly contribute to either the kicking or supporting leg to emphasise the action of soccer kicks.     

Metabolic demand and muscle damage induced by eccentric cycling of knee extensor and flexor muscles

The aim of this study was to examine the metabolic demand and extent of muscle damage of eccentric cycling targeting knee flexor (FLEX) and knee extensor (EXT) muscles. Methods: Eight sedentary men (23.3?±?0.7?y) underwent two eccentric cycling sessions (EXT and FLEX) of 30?min each, at 60% of the maximum power output. Oxygen consumption (VO₂), heart rate (HR) and rated perceived exertion (RPE) were measured during cycling. Countermovement and squat jumps (CMJ and SJ), muscle flexibility, muscle soreness and pain pressure threshold (PPT) of knee extensor and flexor muscles were measured before, immediately after and 1–4 days after cycling. Results: FLEX showed greater VO₂ (+23%), HR (+14%) and RPE (+18%) than EXT. CMJ and SJ performance decreased similarly after cycling. Muscle soreness increased more after EXT than FLEX and PPT decreased in knee extensor muscles after EXT and decreased in knee flexor muscles after FLEX. Greater loss of muscle flexibility in knee flexor muscles after FLEX was observed. Conclusion: Eccentric cycling of knee flexor muscles is metabolically more demanding than that of knee extensors, however muscle damage induced is similar. Knee flexors experienced greater loss of muscle flexibility possibly due to increased muscle stiffness following eccentric contractions.     

Muscle activation sequencing of leg muscles during linear glide shot putting

In the shot put, the athlete’s muscles are responsible for generating the impulses to move the athlete and project the shot into the air. Information on phasic muscle activity is lacking for the glide shot put event and therefore important technical information for coaches is not currently available. This study provides an electromyography (EMG) analysis of the muscle activity of the legs during shot put. Fifteen right-handed Irish national level shot putters performed six maximum effort throws using the glide shot put technique. EMG records of eight bilateral lower limb muscles (rectus femoris, biceps femoris, medial- and lateral-gastrocnemius) were obtained during trials. Analysis using smooth EMG linear envelopes revealed patterns of muscle activity across the phases of the throw and compare men and women performers. The results showed that the preferred leg rectus femoris, the preferred leg biceps femoris and the non-preferred leg biceps femoris play important roles in the glide technique, with the total duration of high volumes of activity between 34 and 53% of the throw cycle. A comprehensive understanding of movement and muscle activation patterns for coaches could be helpful to facilitate optimal technique throughout each of the key phases of the event.     

Isokinetic imbalance of hip muscles in soccer players with osteitis pubis

Abstract

In this study, we compared the isokinetic torques of hip flexors/extensors and abductors/adductors in soccer players suffering from osteitis pubis (OP), with normal soccer players. Twenty soccer male athletes with OP and 20 normal soccer athletes were included in this study. Peak torque/body weight (PT/BW) was recorded from hip flexor/extensor and abductor/adductor muscles during isokinetic concentric contraction modes at angular velocity of 2.1 rad · s^?1, for both groups. The results showed a significant difference between the normal and OP groups for hip flexors (P < 0.05). The normal group had significant, lower PT/BW value than the OP group for their hip flexors (P < 0.05). The hip flexor/extensor PT ratio of OP affected and non-affected limbs was significantly different from that of normal dominant and non-dominant limbs. There were no significant differences between the normal and OP groups for hip extensor, adductor and abductor muscles (P > 0.05). Regarding the hip adductor/abductor PT ratio, there was no significant difference between the normal and OP groups of athletes (P > 0.05). The OP group displayed increase in hip flexor strength that disturbed the hip flexor/extensor torque ratio of OP. Therefore, increasing the hip extensor strength should be part of rehabilitation programmes of patients with OP.     

Electromyographic analysis of lower limb muscles during the golf swing performed with three different clubs

The aim of this study was to describe and compare the EMG patterns of select lower limb muscles throughout the golf swing, performed with three different clubs, in non-elite middle-aged players. Fourteen golfers performed eight swings each using, in random order, a pitching wedge, 7-iron and 4-iron. Surface electromyography (EMG) was recorded bilaterally from lower limb muscles: tibialis anterior, peroneus longus, gastrocnemius medialis, gastrocnemius lateralis, biceps femoris, semitendinosus, gluteus maximus, vastus medialis, rectus femoris and vastus lateralis. Three-dimensional high-speed video analysis was used to determine the golf swing phases. Results showed that, in average handicap golfers, the highest muscle activation levels occurred during the Forward Swing Phase, with the right semitendinosus and the right biceps femoris muscles producing the highest mean activation levels relative to maximal electromyography (70–76% and 68–73% EMG_MAX, respectively). Significant differences between the pitching wedge and the 4-iron club were found in the activation level of the left semitendinosus, right tibialis anterior, right peroneus longus, right vastus medialis, right rectus femuris and right gastrocnemius muscles. The lower limb muscles showed, in most cases and phases, higher mean values of activation on electromyography when golfers performed shots with a 4-iron club.     

Acute and sub-acute effects of repetitive kicking on hip adduction torque in injury-free elite youth soccer players

Abstract

Hip adduction strength is important for kicking and acceleration in soccer players. Changes in hip adduction strength may therefore have an effect on soccer players’ athletic performance. The purpose of this study was to investigate the acute and sub-acute effects of a kicking drill session on hip strength, concerning isometric hip adduction, abduction and flexion torque of the kicking leg and the supporting leg. Ten injury-free male elite soccer players, mean ± s age of 15.8 ± 0.4 years participated. All players underwent a specific 20 min kicking drill session, comprising 45 kicks. The players were tested the day before, 15 min after and 24 h after the kicking drill session by a blinded tester using a reliable test procedure. The isometric hip-action and leg-order were randomized. For the kicking leg, hip adduction torque increased from 2.45 (2.19–2.65) Nm ? kg^?1, median (25th–75th percentiles), at pre-kicking to 2.65 (2.55–2.81) Nm ? kg^?1 (P = 0.024) 24 h post-kicking. This may have implications for the soccer player’s ability to maximally activate the hip adductors during kicking and acceleration, and thereby improve performance the day after a kicking drill session.     

The effects of a 4-week static stretching programme on the individual muscles comprising the hamstrings

The aims of this study were to investigate the effects of a 4-week intervention of static stretching (SS) on muscle hardness of the semitendinosus (ST), semimembranosus (SM) and biceps femoris (BF) muscles. Shear elastic modulus was measured by using ultrasound shear wave elastography as the index of muscle hardness. Thirty healthy men (age 22.7 ± 2.2 years) volunteered for this study and were randomly assigned to the SS intervention group (n = 15) or the control group (n = 15). Participants in the SS intervention group received a 4-week stretch intervention for the hamstrings of their dominant leg. Shear elastic moduli of the hamstrings were measured at initial evaluation and after 4 weeks in both groups at a determined angle. In all muscles, the shear elastic modulus decreased significantly after SS intervention. The percentage change in the shear elastic modulus from the value at initial evaluation to after 4 weeks intervention was greatest in the SM. These results suggest that SS intervention has chronic effects on reducing hardness of the hamstring muscle components, especially the SM muscle.     

Fingertip force and electromyography of finger flexor muscles during a prolonged intermittent exercise in elite climbers and sedentary individuals

Abstract

The aim of this study was to characterize forearm muscle fatigue identified by the decrease in electromyogram median frequency and/or fingertip force during intermittent exercise. Nine elite climbers (international competitive level, USA 5.14a on sight) and ten non-climbers were instructed to maintain a fingertip force of 80% of their maximal voluntary contraction force on a dynamometer mimicking a rock climbing grip during a 5 s effort/5 s rest cycle for 36 repetitions (i.e. 6 min of exercise). Elite climbers lasted twice as long as non-climbers (climbers: 3 min; non-climbers: 1 min 30 s) before the force could no longer be maintained (i.e. the failure point). After this moment, fingertip force decreased and stabilized until the end of the exercise around 50% maximum voluntary contraction force in non-climbers and 63% in elite climbers. Electromyogram median frequency showed a greater decrease in non-climbers than in elite climbers before the failure point. No change in median frequency was observed after the failure point in elite climbers or in non-climbers. These results confirm that elite climbers are better adapted than non-climbers for performing the intermittent fingertip effort before the failure point. After this point, the better fingertip force of elite climbers suggests different forearm muscle properties, while the electromyography results do not provide any indication about the fatigue process.     

Electromyographic analyses of the erector spinae muscles during golf swings using four different clubs

The purpose of this study was to compare the electromyography (EMG) patterns of the thoracic and lumbar regions of the erector spinae (ES) muscle during the golf swing whilst using four different golf clubs. Fifteen right-handed male golfers performed a total of twenty swings in random order using the driver, 4-iron, 7-iron and pitching-wedge. Surface EMG was recorded from the lead and trail sides of the thoracic and lumbar regions of the ES muscle (T8, L1 and L5 lateral to the spinous-process). Three-dimensional high-speed video analysis was used to identify the backswing, forward swing, acceleration, early and late follow-through phases of the golf swing. No significant differences in muscle-activation levels from the lead and trail sides of the thoracic and lumbar regions of the ES muscle were displayed between the driver, 4-iron, 7-iron and pitching-wedge (P > 0.05). The highest mean thoracic and lumbar ES muscle-activation levels were displayed in the forward swing (67–99% MVC) and acceleration (83–106% MVC) phases of the swing for all clubs tested. The findings from this study show that there were no significant statistical differences between the driver, 4-iron, 7-iron and pitching-wedge when examining muscle activity from the thoracic and lumbar regions of the ES muscle.     

2011年大邱田径世界锦标赛世界田坛竞争格局及我国田径发展状况分析

运用文献资料法、逻辑分析法、数理统计法和专家访谈法,对第13届大邱世界田径锦标赛男女共47个项目的所有奖牌归属以及我国参赛运动员决赛成绩排名前八位的项目进行数理统计和归纳分析,对世界田坛实力格局的演变进行客观深入地描述,揭示当今世界田坛的实力格局发展变化的特点,探寻各参赛国的实力、优势项群的地域归属,从而较为准确地掌握世界田径运动的发展方向,同时对我国在本届世锦赛上的成绩表现进行系统的分析,探寻我国田径项目发展的特点和走向以及在发展中存在的问题,以期为我国田径运动优势项目的确立和今后的发展以及备战2012年伦敦奥运会提供参考依据。     

Effects of radiant heat exposure on pacing pattern during a 15-km cycling time trial

Abstract

The goal of this study was to investigate the effects of different durations of skin temperature manipulation on pacing patterns and performance during a 15-km cycling time trial. Nineteen well-trained men completed three 15-km cycling time trials in 18°C and 50% relative humidity with 4.5-km (short-heat), 9.0-km (long-heat) or without (control) radiant heat exposure applied by infrared heaters after 1.5 km in the time trial. During the time trials, power output, mean skin temperature, rectal temperature, heart rate and rating of perceived exertion were assessed. The radiant heat exposure resulted in higher mean skin temperature during the time trial for short-heat (35.0 ± 0.6°C) and long-heat (35.3 ± 0.5°C) than for control (32.5 ± 1.0°C; P < 0.001), whereas rectal temperature was similar (P = 0.55). The mean power output was less for short-heat (273 ± 8 W; P = 0.001) and long-heat (271 ± 9 W; P = 0.02) than for control (287 ± 7 W), but pacing patterns did not differ (P = 0.55). Heart rate was greatest in control (177 ± 9 beats · min^?1; P < 0.001), whereas the rating of perceived exertion remained similar. We concluded that a radiant heat exposure and associated higher skin temperature reduced overall performance, but did not modify pacing pattern during a 15-km cycling time trial, regardless of the duration of the exposure.     

紧身压迫对踏蹬至疲劳过程中股直肌表面肌电特征的影响

目的:利用表面肌电指标定量反映中度和高度紧身压迫在恒定负荷踏蹬至疲劳过程中对股直肌sEMG特征的影响,并探讨其内在机制,以期为紧身运动服装在运动实践中的应用提供科学理论依据.方法:以12名年龄在20～25岁之间的健康男性大学生为试验对象,在3种不同程度紧身压迫状态下,分别以中强度和大强度负荷在功率自行车上进行恒速踏蹬运动至疲劳,共计6次测试;在对受试者一侧下肢股直肌的iEMG和MPF肌电指标进行监测记录和信号处理后,采用双因素方差分析进行试验数据间差异的统计和比较.结果:(1)与无紧身压迫相比,外加中度紧身压迫在中等强度踏蹬运动中,对股直肌iEMG及MPF的整体变化特征无明显影响;(2)外加中度紧身压迫在大强度踏蹬运动后期,以及外加高度紧身压迫在中强度踏蹬运动后期,均使股直肌iEMG(％)值的总体增长幅度较无紧身压迫时有所减少,MPF(％)值的总体降低趋势较无紧身压迫时有所下降;(3)外加高度紧身压迫在大强度踏蹬运动后期,使股直肌iEMG(％)值的总体增长幅度较无紧身压迫时有所增加,MPF(％)值的总体降低趋势较无紧身压迫时有所上升.     

灰色关联分析法在田径技术分析中的适用性研究

灰色关联分析法是进行灰色系统分析的一种常用工具，在田径技术研究过程中被经常采用。很多研究在田径技术分析中使用灰色关联分析方法时，没有考虑到它的局限性，使用时对数据处理不当，致使部分研究结果与实际相悖。本研究的主要目的是为田径技术分析中如何合理运用灰色关联分析法提供理论依据。     

The impact of organizational capacity on voluntary engagement in sports clubs: A multi-level analysis

As volunteerism occurs in an organizational context, both individual factors and organizational characteristics affect (potential) volunteers in sports clubs. Whereas a number of researchers have studied individual-level determinants, knowledge on the role of organizational-level factors is limited. Based on the concept of organizational capacity, in the present study, the authors investigate whether and how human resources, financial, and structural capacities of sports clubs influence individual voluntary engagement. Using data from German football and track and field clubs (n = 296) and their members (n = 1222), the effects of organizational capacity on voluntary engagement within two subsamples, adult members and parents of underage members, are examined. The results of multi-level mixed effects regression analyses show that all capacity dimensions are significantly associated with voluntary engagement of both adult members and parents of underage members. A larger number of members and a greater share of volunteers reduce the amount of time a volunteer devotes to voluntary work; adult members are less likely to volunteer when their club has a balanced budget; and strategic planning increases the likelihood of individuals to volunteer informally. Overall, the results support the notion that the organizational context is more relevant to volunteering of adult members than individual characteristics and equally relevant to parents of underage members. Managerial implications to facilitate volunteering, such as shifting club goals towards youth development and sports for all provision, are discussed.     

Effect of environmental feedbacks on pacing strategy and affective load during a self-paced 30 min cycling time trial

The purpose of this study was to analyze the pacing strategy and its affective consequences during self-paced cycling time trials (TT) performed at different severity of hypoxia. Eight competitive cyclists performed five 30 min self-paced TTs at their best performance in the following conditions: 1) normobaric normoxia (NN_SL); 2) normobaric hypoxia under two simulated altitudes: 2000 m (NH₂₀₀₀) and 3500 m (NH₃₅₀₀) and 3) normobaric hypoxia but the cyclists were deceived and thought to be at sea level for 2000 m (DecNH₂₀₀₀) and 3500 m (DecNH₃₅₀₀). Power Output (PO), oxygen uptake (VO₂), and blood lactate concentration ([La]) were recorded to assess exercise intensity and physiological adaptations. The rate of perceived exertion (RPE) and pleasure were measured with a CR10 Borg scale to evaluate the affective load (AL). PO and VO₂ decreased with the severity of hypoxia but no significantly difference on performance was measured between deceived and real conditions, except for pacing strategy. The started intensity depends on the exercise expectations, but PO was rapidly adjusted with the physiological constraints and the rate of increase of RPE. Finally, AL did not reach maximal values so that the athletes sustained a physiological and emotional reserve to perform a final spurt.     

Effect of different velocity loss thresholds during a power-oriented resistance training program on the mechanical capacities of lower-body muscles

This study compared the effects of two velocity loss thresholds during a power-oriented resistance training program on the mechanical capacities of lower-body muscles. Twenty men were counterbalanced in two groups (VL10 and VL20) based on their maximum power capacity. Both groups used the same exercises, relative intensity and repetition volume, only differing in the velocity loss threshold of each set (VL10: 10% vs. VL20: 20%). Pre- and post-training assessments included an incremental loading test and a 15-m linear sprint to assess the force- and load-velocity relationships and athletic performance variables, respectively. No significant between-group differences (P > 0.05) were observed for the force-velocity relationship parameters (ES range = 0.15–0.42), the MPV attained against different external loads (ES range = 0.02–0.18) or the 15-m sprint time (ES = 0.09). A high between-participants variability was reported for the number of repetitions completed in each training set (CV = 30.3% for VL10 and 29.4% for VL20). These results suggest that both velocity loss thresholds induce similar changes on the lower-body function. The high and variable number of repetitions completed may compromise the velocity-based approach for prescribing and monitoring the repetition volume during a power-oriented resistance training program conducted with the countermovement jump exercise.     

The impact of uphill cycling and bicycle suspension on downhill performance during cross-country mountain biking

ABSTRACT

Non-propulsive work demand has been linked to reduced energetic economy of cross-country mountain biking. The purpose of this study was to determine mechanical, physiological and performance differences and observe economy while riding a downhill section of a cross-country course prior to and following the metabolic “load” of a climb at race pace under two conditions (hardtail and full suspension) expected to alter vibration damping mechanics. Participants completed 1 lap of the track incorporating the same downhill section twice, under two conditions (hardtail and full suspension). Performance was determined by time to complete overall lap and specific terrain sections. Power, cadence, heart rate and oxygen consumption were sampled and logged every second while triaxial accelerometers recorded accelerations (128 Hz) to quantify vibration. No differences between performance times (P = 0.65) or power outputs (P = 0.61) were observed while physiological demand of loaded downhill riding was significantly greater (P < 0.0001) than unloaded. Full suspension decreased total vibrations experienced (P < 0.01) but had no effect on performance (P = 0.97) or physiological (P > 0.05) measures. This study showed minimal advantage of a full suspension bike in our trial, with further investigations over a full race distance warranted.     

Effects of periodic carbohydrate ingestion on endurance and cognitive performances during a 40-km cycling time-trial under normobaric hypoxia in well-trained triathletes

The purpose of this study was to examine CHO ingestion on a cognitive task using a field-simulated time-trial (TT) under hypoxia in well-trained triathletes. Ten male triathletes (age: 22.1 ± 1.1 years; VO₂max: 59.4 ± 1.4 ml/kg/min) participated in this double-blind/crossover/counter-balanced design study. Participants completed 3 TT trials: 1) normoxic placebo (NPLA; FiO₂ = 20.9%), 2) hypoxic placebo (HPLA; FiO₂ = 16.3%), and 3) hypoxic CHO (HCHO; 6% CHO provided as 2 ml/kg/15 min; FiO₂ = 16.3%). During the TT, physiological responses (SpO₂, HR, RPE, and blood glucose/lactate), cognitive performance, and cerebral haemodynamics were measured. Hypoxia reduced TT performance by ~3.5–4% (p < 0.05), but CHO did not affect TT performance under hypoxia. For the cognitive task, CHO slightly preserved exercise-induced cognitive reaction speed but did not affect response accuracy during hypoxic exercise. However, CHO did not preserve the decreased Hb-Diff (cerebral blood flow, CBF) and increased HHb in the prefrontal lobe (p < 0.05) during hypoxic exercise, and CHO failed to preserve hypoxia-suppressed prefrontal CBF and tissue oxygen saturation. In conclusion, the present study demonstrates that CHO is effective in sustaining reaction speed for a cognitive task but not promoting TT performance during hypoxic exercise, which would be important for strategy-/decision-making when athletes compete at moderate high-altitude.     

Acute effects of small changes in crank length on gross efficiency and pedalling technique during submaximal cycling

ABSTRACT

The main purpose of this study was to assess the acute effects of small changes in crank length (assumable by competitive cyclists) on metabolic cost and pedalling technique during submaximal cycling. Twelve amateur road cyclists performed three sets of submaximal pedalling (150, 200 and 250 W) at a constant cadence (91.3 ± 0.8 rpm) in a randomised order with three commonly used crank lengths, preferred (172.5–175 mm), +5 mm and ?5 mm. Energy cost of pedalling, kinetic and kinematic variables were simultaneously registered. Changes in crank length had no significant effect on heart rate (144 ± 13, 145 ± 12 and 145 ± 13 bpm, respectively) and gross efficiency (GE) (20.4 ± 2.1, 20.1 ± 2.2 and 20.3 ± 2.4%, respectively). A longer crank induced a significant (P < 0.05) reduction of positive impulse proportion (PIP) (0.9–1.9%) due to a greater maximum (1.0–2.3 N · m) and minimum torque (1.0–2.2 N · m). At the same time, the maximum flexion and range of motion of the hip and knee joints were significantly increased (1.8–3.4° and P < 0.05), whereas the ankle joint was not affected. In conclusion, the biomechanical changes due to a longer crank did not alter the metabolic cost of pedalling, although they could have long-term adverse effects. Therefore, in case of doubt between two lengths, the shorter one might be recommended.