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1.
Cross-country mountain bike suspension reportedly enhances comfort and performance through reduced vibration and impact exposure. This study analysed the effectiveness of three different front fork systems at damping accelerations during the crossing of three isolated obstacles (stairs, drop, and root). One participant completed three trials on six separate occasions in a randomised order using rigid, air-sprung, and carbon leaf-sprung forks. Performance was determined by time to cross obstacles, while triaxial accelerometers quantified impact exposure and damping response. Results identified significant main effect of fork type for performance time (p < 0.05). The air-sprung and leaf-sprung forks were significantly slower than the rigid forks for the stairs (p < 0.05), while air-sprung suspension was slower than the rigid for the root protocol (p < 0.05). There were no differences for the drop protocol (p < 0.05). Rigid forks reduced overall exposure (p < 0.05), specifically at the handlebars for the stairs and drop trials. More detailed analysis presented smaller vertical accelerations at the handlebar for air-sprung and leaf-sprung forks on the stairs (p < 0.05), and drop (p < 0.05) but not the root. As such, it appears that the suspension systems tested were ineffective at reducing overall impact exposure at the handlebar during isolated aspects of cross-country terrain features which may be influenced to a larger extent by rider technique.  相似文献   

2.
Show‐Jumping     
This study examined the effects of the rider on the linear projectile kinematics of show‐jumping horses. SVHS video recordings (50 Hz) of eight horses jumping a vertical fence 1 m high were used for the study. Horses jumped the fence under two conditions: loose (no rider or tack) and ridden. Recordings were digitised using Peak Motus. After digitising the sequences, each rider's digitised data were removed from the ridden horse data so that three conditions were examined: loose, ridden (including the rider's data) and riderless (rider's data removed). Repeated measures ANOVA revealed significant differences between ridden and loose conditions for CG height at take‐off (p < 0.001), CG distance to the fence at take‐off (p = 0.001), maximum CG during the suspension phase (p < 0.001), CG position over the centre of the fence (p < 0.001), CG height at landing (p < 0.001), and vertical velocity at take‐off (p < 0.001). The results indicated that the rider's effect on jumping horses was primarily due to behavioural changes in the horse's motion (resulting from the rider's instruction), rather than inertial effects (due to the positioning of the rider on the horse). These findings have implications for the coaching of riders and horses.  相似文献   

3.
Vibration in cycling has been proved to have undesirable effects over health, comfort and performance of the rider. In this study, 15 participants performed eight 6-min sub-maximal pedalling exercises at a constant power output (150W) and pedalling cadence (80 RPM) being exposed to vibration at different frequencies (20, 30, 40, 50, 60, 70 Hz) or without vibration. Oxygen uptake (VO2), heart rate (HR), surface EMG activity of seven lower limb muscles (GMax, RF, BF, VM, GAS, SOL and TA) and 3-dimentional accelerations at ankle, knee and hip were measured during the exercises. To analyse the dynamic response, the influence of the pedalling movement was taken into account. The results show that there was not significant influence of vibrations on HR and VO2 during this pedalling exercise. However, muscular activity presents a significant increase with the presence of vibration that is influenced by the frequency, but this increase was very low (< 1%). Also, the dynamic response shows an influence of the frequency as well as an influence of the different parts of the pedalling cycle. Those results help to explain the effects of vibration on the human body and the influence of the rider/bike interaction in those effects.  相似文献   

4.
This study examined the effects of the rider on the linear projectile kinematics of show-jumping horses. SVHS video recordings (50 Hz) of eight horses jumping a vertical fence 1 m high were used for the study. Horses jumped the fence under two conditions: loose (no rider or tack) and ridden. Recordings were digitised using Peak Motus. After digitising the sequences, each rider's digitised data were removed from the ridden horse data so that three conditions were examined: loose, ridden (including the rider's data) and riderless (rider's data removed). Repeated measures ANOVA revealed significant differences between ridden and loose conditions for CG height at take-off (p < 0.001), CG distance to the fence at take-off (p = 0.001), maximum CG during the suspension phase (p < 0.001), CG position over the centre of the fence (p < 0.001), CG height at landing (p < 0.001), and vertical velocity at take-off (p < 0.001). The results indicated that the rider's effect on jumping horses was primarily due to behavioural changes in the horses motion (resulting from the rider's instruction), rather than inertial effects (due to the positioning of the rider on the horse). These findings have implications for the coaching of riders and horses.  相似文献   

5.
In this study, we examined the effect of string vibration damping devices on reducing racket frame vibration transfer to the forearm. Twenty participants volunteered to hold a tennis racket stationary in a forehand and backhand stroking position while tennis balls were fired at 20 m?·?s?1 towards two impact locations, the node of vibration and the dead spot. A three-way analysis of variance with repeated measures on damping condition, impact location and stroke condition was performed on the data. The resonant frequency of the hand-held racket was found to be ～120 Hz. No significant differences in amplitude of vibration at the resonant frequency were found for the wrist or the elbow when damped and non-damped impacts were compared. Impacts at the dead spot produced greater amplitudes of vibration (P <?0.01) but no interaction between impact location and string dampers was evident. The string dampers had no effect on the grip force used or the muscle electrical activity in the forearm after impact. In conclusion, we found that string dampers do not reduce the amount of racket frame vibration received at the forearm. We suggest that string dampers remain a popular accessory among tennis players because of their acoustic effects and psychological support rather than any mechanical advantage.  相似文献   

6.
In this study, we examined the effect of string vibration damping devices on reducing racket frame vibration transfer to the forearm. Twenty participants volunteered to hold a tennis racket stationary in a forehand and backhand stroking position while tennis balls were fired at 20 m x s(-1) towards two impact locations, the node of vibration and the dead spot. A three-way analysis of variance with repeated measures on damping condition, impact location and stroke condition was performed on the data. The resonant frequency of the hand-held racket was found to be approximately 120 Hz. No significant differences in amplitude of vibration at the resonant frequency were found for the wrist or the elbow when damped and non-damped impacts were compared. Impacts at the dead spot produced greater amplitudes of vibration (P < 0.01) but no interaction between impact location and string dampers was evident. The string dampers had no effect on the grip force used or the muscle electrical activity in the forearm after impact. In conclusion, we found that string dampers do not reduce the amount of racket frame vibration received at the forearm. We suggest that string dampers remain a popular accessory among tennis players because of their acoustic effects and psychological support rather than any mechanical advantage.  相似文献   

7.
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.  相似文献   

8.
A forward dynamics computer simulation for replicating tennis racket/ball impacts is described consisting of two rigid segments coupled with two degrees of rotational freedom for the racket frame, nine equally spaced point masses connected by 24 visco-elastic springs for the string-bed and a point mass visco-elastic ball model. The first and second modal responses both in and perpendicular to the racket string-bed plane have been reproduced for two contrasting racket frames, each strung at a high and a low tension. Ball/string-bed normal impact simulations of real impacts at nine locations on each string-bed and six different initial ball velocities resulted in <3% RMS error in rebound velocity (over the 16–27 m/s range observed). The RMS difference between simulated and measured oblique impact rebound angles across nine impact locations was 1°. Thus, careful measurement of ball and racket characteristics to configure the model parameters enables researchers to accurately introduce ball impact at different locations and subsequent modal response of the tennis racket to rigid body simulations of tennis strokes without punitive computational cost.  相似文献   

9.
Whole body vibration (WBV) is used as a training method but its physical risk is not yet clear. Hence, the aim of this study is to assess the exposure to WBV by a measure of acceleration at the lower limb under dynamic and static postural conditions. The hypothesis of this paper is that this assessment is influenced by the frequency, position, and movement of the body. Fifteen healthy males are exposed to vertical sinusoidal vibration at different frequencies (20–60 Hz), while adopting three different static postures (knee extension angle: 180°, 120° and 90°) or performing a dynamic half-squat exercise. Accelerations at input source and at three joints of the lower limb (ankle, knee, and hip) are measured using skin-mounted accelerometers. Acceleration values (g) in static conditions show a decrease in the vibrational dose when it is measured at a more proximal location in the lower extremity. The results of the performed statistical test show statistically significant differences (p < 0.05) in the transmissibility values caused by the frequency, the position, and to the presence of the movement and its direction at the different conditions. The results confirm the initial hypothesis and justify the importance of a vibration assessment in dynamic conditions.  相似文献   

10.
振动波方向、频率对振动训练的影响   总被引：2，自引：0，他引：2  
研究不同方向的振动波、振动频率在振动训练中对肌肉力量的影响。通过对人体在负重蹲练习时附加不同振动方向、振动频率的振动刺激,测量训练前后等速肌力矩峰值、功率等指标。经对测量数据对比分析发现,水平方向和多维方向振动波的训练效果要优于垂直方向;在15～45Hz振动频率范围内,振动训练的效果有明显增加的趋势。振动训练采用水平或多维方向的振动波,以及振动频率大于30Hz时,可收到较好训练效果。  相似文献   

11.
Abstract

The aim of the study was to determine whether vibration applied directly to a muscle-tendon could enhance neuromuscular output during and 1.5 and 10 min after a bout of ballistic resistance training. Fourteen participants were exposed to two training conditions in random order: exercise with vibration and exercise with sham vibration. The exercise comprised three sets of ballistic knee extensions with a load of 60–70% of one-repetition maximum. Vibration (1.2 mm amplitude, 65 Hz frequency) was applied with a portable vibrator strapped over the distal tendon of the quadriceps. Knee joint angular velocity, moment, and power, and rectus femoris and vastus lateralis electromyography root-mean-squared were measured during knee extension. During and after training, the vibration did not induce significant changes in peak angular velocity, time to peak angular velocity, peak moment, time to peak moment, peak power, time to peak power, or average EMG of the rectus femoris and vastus lateralis. We conclude that direct vibration, at the selected amplitude and frequency, does not enhance these neuromuscular variables in ballistic knee extensions during or immediately after training.  相似文献   

12.
采用PHYSIO PLATE振动训练台,对北京优秀垒球、女子游泳及女子跳水运动员进行同振幅下不同频率振动刺激力量训练,并采用MERAC等速肌力测试系统,对实验前后以及实验中运动员下肢肌力变化情况进行对比研究。研究发现,抗负荷力量训练附加振动刺激可以有效地提高力量训练的效果,能够以相对较小的负荷有效地提高肌肉的最大力量、爆发力以及肌肉耐力;同振幅下,次高频(35Hz～50Hz)振动刺激对肌肉最大力量、快速力量、爆发力以及肌肉耐力的训练效果显著高于中低频(25Hz～35Hz)振动刺激。  相似文献   

13.
Abstract Whole-body vibration training improves strength and can increase maximal oxygen consumption ([Vdot]O(2max)). No study has compared the metabolic demand of synchronous and side-alternating whole-body vibration. We measured [Vdot]O(2) and heart rate during a typical synchronous or side-alternating whole-body vibration session in 10 young female sedentary participants. The 20-min session consisted of three sets of six 45-s exercises, with 15?s recovery between exercises. Three conditions wererandomly tested on separate days: synchronous at 35?Hz and 4?mm amplitude, side-alternating at 26?Hz and 7.5?mm amplitude (peak acceleration matched at 20?g in both vibration conditions), and no vibrations. Mean [Vdot]O(2) (expressed as %[Vdot]O(2max)) did not differ between conditions: 29.7?±?4.2%, 32.4?±?6.5%, and 28.7?±?6.7% for synchronous, side-alternating, and no vibrations respectively (P?=?0.103). Mean heart rate (% maximal heart rate) was 65.6?±?7.3%, 69.8?±?7.9%, and 64.7?±?5.6% for synchronous, side-alternating, and no vibrations respectively, with the side-alternating vibrations being significantly higher (P?=?0.019). When analysing changes over exercise sessions, mean [Vdot]O(2) was higher for side-alternating (P?相似文献   

14.
Little is known about the transmission of vibration to the head when using whole-body vibration (WBV) training machines. This paper investigates the effect of frequency and posture on the transmission of vibration from a vibrating plate to the head of standing people. Nine male participants were exposed to vertical vibration at nine frequencies in the range of 17–46 Hz and vibration acceleration in the range of 7.85–18.64 m/s2 (peak). The participants adopted four standing postures described as standing with locked knee (LK), bent knee (BK), one leg (OL), and one foot to the front and the other to the back (FB). The transmissibility to the head differed among postures (t-test, p < 0.05) and was greatest with the FB posture and smallest with the BK posture. The transmissibility to the head decreased with increasing the frequency (t-test, p < 0.05) but the extent of the decrease depended on the adopted posture. This frequency-posture interaction effect on the transmissibility should be considered when designing a training program. The data will be useful for developing standards/protocols that govern the use of WBV machines as well as for building human body models that can predict potential risks arising from using WBV machines.  相似文献   

15.
The aim of the study was to determine whether vibration applied directly to a muscle-tendon could enhance neuromuscular output during and 1.5 and 10 min after a bout of ballistic resistance training. Fourteen participants were exposed to two training conditions in random order: exercise with vibration and exercise with sham vibration. The exercise comprised three sets of ballistic knee extensions with a load of 60-70% of one-repetition maximum. Vibration (1.2 mm amplitude, 65 Hz frequency) was applied with a portable vibrator strapped over the distal tendon of the quadriceps. Knee joint angular velocity, moment, and power, and rectus femoris and vastus lateralis electromyography root-mean-squared were measured during knee extension. During and after training, the vibration did not induce significant changes in peak angular velocity, time to peak angular velocity, peak moment, time to peak moment, peak power, time to peak power, or average EMG of the rectus femoris and vastus lateralis. We conclude that direct vibration, at the selected amplitude and frequency, does not enhance these neuromuscular variables in ballistic knee extensions during or immediately after training.  相似文献   

16.
Abstract

The aim of this study was to assess the effects of 8 weeks of whole-body vibrations on explosive and reactive leg strength. Thirty-three physically active students took part in the study and were randomly assigned to an individualized-vibration group, a fixed-vibration group or a control group. The frequency of vibration was set to 30 Hz for the fixed-vibration group, whereas the frequency for the individualized-vibration group was determined by monitoring the participants' EMGrms activity. The participants in the two vibration groups were exposed three times a week for 8 weeks to a series of 10 × 1-min whole-body vibrations with a 1-min pause between series of vibrations and a 4-min pause after the first five series of vibrations. Jump height in the squat jump increased significantly in all three groups (by 11% for the individualized-vibration group, p = 0.001; by 3% for the fixed-vibration group, p = 0.011; and by 2% for the control group, p = 0.006), but countermovement jump height was not affected. In continuous rebound jumps by the individualized-vibration group, jumping height increased by 22% (p = 0.006) and power increased by 18% (p = 0.002). The results of this study suggest that the use of an individualized vibration frequency produces a greater response from the neuromuscular system and is more beneficial than vibrations at a fixed pre-selected frequency.  相似文献   

17.
ABSTRACT

The sound resulting from the impact of a table tennis racket and ball can influence a player’s perception of equipment quality in addition to providing clues to personal performance. This study explores the vibrational modes of both racket and ball and how those modes contribute to the impact sound. Experimental modal analysis reveals that the racket exhibits a large number of structural vibration modes typical of elliptical plates. Acoustic analysis reveals that two of those structural modes dominate the sound produced by the ball-paddle impact. The rubber padding provides some damping and a significant mass loading to the racket vibrations. The hollow cellulose nitrate balls exhibit vibrational modes typical of a hollow spherical shell, starting with frequencies around 5920 Hz. Experimental frequencies confirm theoretical and computational models. However, the contact time between racket and ball is long enough that the lowest acoustic modes of the ball do not contribute to the radiated sound. Instead, acoustic analysis suggests that the ball appears to radiate sound at a much higher frequency sound (8.5–12 kHz) most likely due to snap-through after buckling common to spherical shells undergoing deformation while impacting a rigid surface at high speeds.  相似文献   

18.
BackgroundThe forefoot running footfall pattern has been suggested to reduce the risk of developing running related overuse injuries due to a reduction of impact related variables compared with the rearfoot running footfall pattern. However, only time-domain impact variables have been compared between footfall patterns. The frequency content of the impact shock and the degree to which it is attenuated may be of greater importance for injury risk and prevention than time-domain variables. Therefore, the purpose of this study was to determine the differences in head and tibial acceleration signal power and shock attenuation between rearfoot and forefoot running.MethodsNineteen habitual rearfoot runners and 19 habitual forefoot runners ran on a treadmill at 3.5 m/s using their preferred footfall patterns while tibial and head acceleration data were collected. The magnitude of the first and second head acceleration peaks, and peak positive tibial acceleration were calculated. The power spectral density of each signal was calculated to transform the head and tibial accelerations in the frequency domain. Shock attenuation was calculated by a transfer function of the head signal relative to the tibia.ResultsPeak positive tibial acceleration and signal power in the lower and higher ranges were significantly greater during rearfoot than forefoot running (p < 0.05). The first and second head acceleration peaks and head signal power were not statistically different between patterns (p > 0.05). Rearfoot running resulted in significantly greater shock attenuation for the lower and higher frequency ranges as a result of greater tibial acceleration (p < 0.05).ConclusionThe difference in impact shock frequency content between footfall patterns suggests that the primary mechanisms for attenuation may differ. The relationship between shock attenuation mechanisms and injury is not clear but given the differences in impact frequency content, neither footfall pattern may be more beneficial for injury, rather the type of injury sustained may vary with footfall pattern preference.  相似文献   

19.
目的:自主动作可以引起感知衰减已经得到前期研究证实,但该现象的时间进程尚不明确,机制也存在争议。研究通过2个实验对上述问题进行探索。方法:实验1共纳入被试12人,使用随机动点运动一致性判断任务,结合信号检测论,探索感知衰减现象的时间进程;实验2共纳入被试14人,采用主观报告法对预激活与抑制假说进行验证。结果:实验1中,将动作执行前后450 ms共900 ms以每150 ms划分为一段,动作执行前300 ms至执行后150 ms的3段时间内,被试的辨别力d’在自主动作效果与刺激对应关系一致条件下显著降低(P均<0.05);其余3段时间内,被试的辨别力d’在自主动作效果与刺激对应关系一致与不一致条件下差异不显著(P均>0.05)。实验2中,被试在刺激强度低的条件下,对与自主动作效果一致的刺激的主观强度报告显著高于不一致的刺激(P<0.05);在刺激强度为高的条件下,对自主动作效果对应一致或不一致的刺激评分无显著差异(P>0.05)。结论:自主动作引起的感知衰减在动作执行前就已经发生,动作执行前的150 ms与执行后的300 ms是重要的时间节点。自主动作可以在两个节点内引起感知衰减,在其他时间无法引起感知衰减。自主动作所引起的感知系统的预激活是感知衰减的成因。  相似文献   

20.
This study investigated the performance-related feasibility and physiological benefits of purposefully eliminating propulsive work while descending in mountain biking and compared values to those measured during road descending. Participants cycled uphill on a road at race pace before descending over three conditions (off-road pedalling; off-road coasting; road coasting). Relatively low power output during off-road pedalling was associated with a greater oxygen uptake (p?<?.01) when compared with off-road coasting despite no difference in vibration exposure (p?>?.05). Importantly, pedalling did not invoke a performance benefit (p?>?.05) on the descent used in this study. Significantly greater heart rate and oxygen uptake (both p?<?.01) were observed between road and off-road descending, likely caused by the increase in terrain-induced vibrations (p?<?.01) experienced between the bicycle and rider. Results indicate that reducing propulsive work during descending can improve recovery without being disadvantageous to performance. Similarly, the vibrations experienced during road descending are relatively low, and further reduce oxygen cost. In an effort to increase efficiency, it is recommended that mountain bike athletes focus on skills to increase descending speed without the addition of pedalling, and that equipment be used to decrease vibrations nearer to those seen on the road.  相似文献   

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