Dynamic Resistance Parameters of Arm Stroke during Swimming

Swimming, as a sport beneficial to body and mind, also has a place in international sports. For swimmers and coaches, it is always the most important to improve the propulsion and reduce the resistance during swimming. This paper briefly introduced the resistance of human body in swimming, described the dynamic resistance of human body in arm stroke, and then introduced the principle of micro disturbance method which was used for measuring the dynamic resistance in swimming. Finally, ten swimmers from school team and ten beginners were tested for the dynamic resistance in freestyle, backstroke and breaststroke when they swam with arm stroke only. After adding micro resistance, the swimming speed of the subjects decreased when they swam with all their strength; the speed of freestyle swimming was the largest, followed by backstroke and breaststroke before and after loading, and the swimming speed of school team members was larger than that of beginners; the dynamic resistance and dynamic resistance coefficient of breaststroke were the largest, backstroke was the second, freestyle was the smallest, and the dynamic resistance and dynamic resistance coefficient of school team members were always smaller than those of beginners no matter the swimmer took which swimming style.     

The aerobic demand of backstroke swimming, and its relation to body size, stroke technique, and performance

Few studies have examined the aerobic demand of backstroke swimming, and its relation to body morphology, technique, or performance. The aims of this study were thus to: i) describe the aerobic demand of backstroke swimming in proficient swimmers at high velocities; ii) assess the effects of body size and stroke technique on submaximal and maximal O2 costs, and; iii) test for a relationship between submaximal O2 costs and maximal performance. Sixteen male competitive swimmers were tested during backstroke swimming at velocities from 1.0 to 1.4 m.s-1. Results showed that VO2 increased linearly with velocity (m.s-1) following the equation VO2 = 6.28v - 3.81 (r = 0.77, SEE/Y = 14.9%). VO2 was also related to the subjects' body mass, height, and armspan. Longer distances per stroke were associated with lower O2 costs, and better maximal performances. A significant relation was found between VO2 at 1.1 m.s-1, adjusted for body mass, and 400 m performance (r = -0.78). Submaximal VO2 was also related to reported times for 100 m and 200 m races. Multiple correlation analyses indicated that VO2 at 1.1 m.s-1 and VO2max accounted for up to 78% of the variance in maximal performances. These results suggest that the assessment of submaximal and maximal VO2 during backstroke swimming may be of value in the training and testing programs of competitive swimmers.     

Energy cost of front-crawl swimming in women

The purpose of this study was to examine the relationship between the energy cost of swimming per unit distance (Cs) at different velocities (v) and performance level, body size and swimming technique in women. A total of 58 females swimmers were studied. Three performance levels (A, B, C) were determined, ranging from the slower (A) to the faster (B, C). At level C and at 1.1 m.s-1, Cs,1.1 was reduced by 7% when directly compared to level B. The Cs,1.1 was reduced by 10% when calculated per unit of height (h) and by 37% when calculated per unit of h and hydrostatic lift (HL). For the whole group of swimmers, the equation regression was Cs,1.1 = 0.27 h-2.38 HL - 7.5 (r = 0.53, P less than 0.01). To evaluate the specific influence of arm length two groups of long- and short-armed swimmers were selected among swimmers of similar h and performance. The Cs was significantly higher (P less than 0.05) by 12%, SD 2.2%, for short-armed than for long-armed swimmers. To evaluate the influence of different types of swimming technique, two other groups of similar performance and anthropometric characteristics were selected. The Cs was significantly higher (P less than 0.05) by 12%, SD 4.5% for swimmers using for preference their legs rather than their arms. The Cs of the sprinters was 15.7%, SD 2% higher than that of the long-distance swimmers. For all groups, Cs increased with v on average by 8% to 11% every 0.1 m.s-1. These findings showed that Cs variations of these women were close to those previously demonstrated for men. The Cs depends on performance level, body size, buoyancy, swimming technique and v.     

Relationships between legs bone mineral density, anthropometry and jumping height in prepubertal children

The aim of this study was to determine how the legs bone mineral density (BMD) is influenced by anthropometry and vertical jumping height in prepubertal children. In total, 64 8-11-year-old schoolchildren (27 boys and 37 girls) were studied. All children were at Tanner stage 1. The subjects' height and body mass were measured and BMI calculated. The following anthropometric parameters directly connected with leg were measured: skinfolds--front thigh and medial calf girths--gluteal, thigh, mid-thigh, calf and ankle; lengths--iliospinale height, trochanterion height, trochanteriontibiale laterale, tibiale-laterale height and tibiale mediale-spyrion tibiale; and breadths--biiliocristal, foot length and biepicondylar femur. Total body and legs fat mass and fat %, lean body mass (LBM) and both legs BMD were measured by DXA. Maximal jumping height was measured on the contact mat. Stepwise multiple regression analysis indicated that body height in boys (54.6%; R2 x 100) and body mass in girls (57.3%) were the most important basic anthropometric parameters that influenced BMD in legs. From the measured skinfolds, that of the front thigh characterized legs BMD by 24.9-35.6%. From the girths, the most important parameter to characterize legs BMD was that of calf (50.0-59.1%). Tibiale laterale height was the only length parameter which was highly related with legs BMD (51.1-54.5%). Biepicondylar femur was the most important breadth parameter which characterized legs BMD (51.0-54.8%). Femur breadth and tibiale-laterale height were selected (68.7%) in boys, and tibiale-laterale height and front thigh skinfold thickness (66.0%) in girls when all measured leg anthropometric parameters were analyzed together. From the body composition parameters, the most important parameter to characterize legs BMD was legs LBM (48.9-59.5%). Jumping height did not correlate with legs BMD in any studied groups. In summary, the present study demonstrated that legs LBM together with tibiale-laterale height are the main predictors of legs BMD in prepubertal children.     

No correlation of anthropometry and race performance in ultra-endurance swimmers at a 12-hours-swim

BACKGROUND: In swimmers, the effects of the anthropometric factors, upper extremity length, hand length and body height, on performance over 100 m have been shown, but no data exist about the influence of anthropometric factors on performance in ultra-endurance swimmers. SUBJECTS AND METHODS: Twelve male Caucasian ultra-swimmers participated in our study at the 9th edition in 2007 of the 12-hours-swim in Zurich, Switzerland. We determined body mass, length of arms and legs, body height, circumferences of extremities, skeletal muscle mass and fat mass in order to correlate with the covered distance and to find an effect on race performance. RESULTS: The 12 swimmers achieved an average distance of 29.4 +/- 5.1 km, varying from 22.8 km to 39.1 km during these 12 hours. There was no correlation between body mass, length of arms and legs, body height, circumferences of extremities, skeletal muscle mass and fat mass to race performance. CONCLUSION: In these 12 male ultra-endurance swimmers no effect of the anthropometric parameters body mass, body height, BMI, circumferences of extremities, length of arms and legs, skeletal muscle mass and fat mass, on performance in a 12-hours-swim has been found.     

The evaluation of the effect of stool height alteration on workload of squatting postures performed by Indonesians with different body mass index (BMI)

Indonesians commonly perform activities on the floor that require squatting postures. It has been identified that adopting squatting postures without any proper support would gradually cause postural stress. This study examines the influence of different squatting heights to the body kinematics and subjective discomfort rating. The subjects were divided into two different body types: overweight subjects with BMI > 24.9 and normal weight subjects with BMI 18-24.9. The subjects adopted a squatting posture at no-stool condition and at the stool height of 10, 15, and 20 cm. The task was to simulate the work close to the ground level with the hip joint deeply flexed. Body segmental angular flexion (SAF) and the visual analog scale (VAS) method were selected for parameter analyses. Significant differences were found in both parameters SAF (trunk, hip, knee, and ankle) and VAS. The interaction effect was found by squatting height and the body type for SAF of the trunk (p < 0.05). However, the increasing BMI index was also found significantly affected associated with the anthropometrical characteristics for buttock height and lower limbs depth. It is suggested that normal weight subjects sit comfortably at 15 cm stool height, whereas overweight subjects preferred 20 cm stool height as a better acceptability condition in terms of overall parameter analyses.     

Effect of wearing clothes on oxygen uptake and ratings of perceived exertion while swimming

For a comparative study between swimming in swimwear (control-sw) and swimming in clothes (clothes-sw), oxygen uptake (VO2) and ratings of perceived exertion (RPE) were measured. The subjects were six male members of a university swimming team. Three swimming strokes--the breaststroke, the front crawl stroke and the elementary backstroke--were applied. With regards to clothes-sw, swimmers wore T-shirts, sportswear (shirt and pants) over swimwear and running shoes. In both cases of control-sw and clothes-sw, the VO2 was increased exponentially with increased swimming speed. The VO2 of the subjects during the clothed tests did not exceed 1.4 times of that in the case of control-sw at swimming speeds below 0.3 m/s. As swimming speeds increased, VO2 difference in both cases increased. Consequently, VO2 in the clothed tests was equal to 1.5-1.6 times and 1.5-1.8 times of that in the swimwear tests at speeds of 0.5 and 0.7 m/s, respectively. At speeds below 0.6 m/s in clothes-sw, the breaststroke showed lower VO2 than the front crawl stroke, and the elementary backstroke showed higher VO2 than the other two swimming strokes. RPE increased linearly with %peak VO2. In addition, any RPE differences among the three swimming strokes were not shown in the control-sw tests. At an exercise intensity above 60 %peak VO2, clothed swimmers showed slightly higher RPE in the front crawl stroke compared to that in the two other swimming strokes.     

Active drag, useful mechanical power output and hydrodynamic force coefficient in different swimming strokes at maximal velocity.

By comparing the time of the same distance swum with and without an added resistance, under the assumption of an equal power output in both cases, the drag of 73 top swimmers was estimated. The active drag Fr(a.d.) at maximal swimming velocities varied considerably across strokes and individuals. In the females Fr(a.d.) ranged from 69.78 to 31.16 N in the front-crawl, from 83.04 to 37.78 N in dolphin, from 93.56 to 45.19 N in breaststroke, and from 65.51 to 37.79 N in back-stroke. In the males Fr(a.d.) ranged from 167.11 to 42.23 N in front-crawl, from 156.09 to 46.95 N in dolphin, from 176.87 to 55.61 N in breaststroke, and from 146.28 to 46.36 N in back-stroke. Also, the ratio of Fr(a.d.) to the passive drag Fr(a.d.) as determined for the analogical velocity in a tugging condition (in standard body position-front gliding) shows considerable individual variations. In the female swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 145.17 to 59.94% in front-crawl, from 192.39 to 85.57% in dolphin, from 298.03 to 124.50% in breaststroke, and from 162.87 to 85.61% in back-stroke. In the male swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 162.24 to 62.39% in front-crawl, from 191.70 to 70.38% in dolphin, from 295.57 to 102.83% in breaststroke, and from 198.82 to 74.48% in back-stroke. The main reason for such variations is found in the individual features of swimming technique and can be quantitatively estimated with the hydrodynamic force coefficient, which thus provides an adequate index of technique.     

Effects of moist heat on hamstring flexibility and muscle temperature

The purpose of this study was to determine whether the application of a moist heat pack (MHP) could increase hamstring flexibility. Both legs for each subject were used for this study. Each leg was randomly assigned to either an MHP leg or a control leg condition. Twenty-seven male subjects (height = 178.5 +/- 8.6 cm; weight = 84.4 +/- 18.7 kg; age = 21.9 +/- 6.3 years) volunteered for this study. For the MHP leg condition, baseline hamstring flexibility was measured using an active knee extension test. A 23-ga indwelling thermistor was inserted to a depth of 2.54 cm to measure hamstring temperature. After baseline temperature was recorded, 2 MHPs were placed on either side of the thermistor until temperature was increased by 0.4 degrees C. Hamstring flexibility postintervention measurements were performed at 0, 4, 8, and 16 minutes. The same protocol was used for the control leg, without the MHP application. A 2 x 5 repeated-measures analysis of variance revealed no significant interaction between the MHP and the control leg condition. These results support previous findings that MHP application does not significantly affect muscle flexibility. After application of an MHP, it takes 20-25 minutes to increase intramuscular temperatures by 0.4 degrees C. Both of these findings should be taken into consideration when using an MHP to increase muscle flexibility.     

Relationship between tethered forces and the four swimming techniques performance

The purpose of the current study was to identify the relationships between competitive performance and tether forces according to distance swam, in the four strokes, and to analyze if relative values of force production are better determinants of swimming performance than absolute values. The subjects (n = 32) performed a 30 s tethered swimming all-out effort. The competitive swimming velocities were obtained in the distances 50, 100 and 200 m using official chronometric values of competitions within 25 days after testing protocol. Mean force and velocity (50 m event) show significant correlations for front crawl (r = .92, p < .01), backstroke (r = .81, p < .05), breaststroke (r = .94, p < .01) and butterfly (r = .92, p < .01). The data suggests that absolute values of force production are more associated to competitive performance than relative values (normalized to body mass). Tethered swimming test seems to be a reliable protocol to evaluate the swimmer stroking force production and a helpful estimator of competitive performance in short distance competitive events.     

KINEMATIC VARIABLES AND BLOOD ACID-BASE STATUS IN THE ANALYSIS OF COLLEGIATE SWIMMERS’ ANAEROBIC CAPACITY

Short duration repeated maximal efforts are often used in swimming training to improve lactate tolerance, which gives swimmers the ability to maintain a high work rate for a longer period of time. The aim of the study was to examine the kinematics of swimming and its relation to the changes in blood acid-base status and potassium level. Seven collegiate swimmers, with at least 6 years of training experience, volunteered to participate in the study. The test consisted of 8 x 25 m front crawl performed with maximum effort. The rest period between repetitions was set to five seconds. Blood samples were taken from the fingertip at rest, after warm-up and in the 3rd minute after completion of the test. The swimming was recorded with a video recorder, for later analysis of time, velocity and technique (stroke index). Based on the swimming velocity results, the obtained curve can be divided into rapid decrease of velocity and relatively stable velocities. The breaking point of repetition in swimming velocity was assumed as the swimming velocity threshold and it was highly correlated with the decrease of the blood acid-base status (pH r=0.82, BE r=0.87, HCO₃ ^- r=0.76; p<0.05 in all cases). There was no correlation between stroke index or fatigue index and blood acid-base status. Analysis of the swimming speed in the 8 x 25 m test seems to be helpful in evaluation of lactate tolerance (anaerobic capacity) in collegiate swimmers.     

Rolling rhythms in front crawl swimming with six-beat kick

The purpose of this study was to establish the rhythm characteristics of skilled front crawl swimmers using a six-beat kick. These included the amplitudes of the first three Fourier harmonics (H1, H2, H3) and their percent contributions to power contained in the angular displacement signals of the shoulders, hips, knees, and ankles with respect to the longitudinal axis in line with the swimming direction. Three-dimensional video data of seven national/international level swimmers were collected during simulated 200 m front crawl races in which swimmers maintained six-beat kicking patterns. Swimmers differed in all variables but had small variability across the four 50 m laps. Modest changes occurred during the 200 m, with the exception of shoulder roll, which remained constant and was represented almost entirely by a single sinusoid (H1). Changes across laps reached significance for swimming speed, stroke rate, hip roll, and H3 wave velocity between the knee and ankle. A H3 body wave of moderate and increasing velocity travelled caudally from hip to ankle. In the light of existing knowledge of aquatic locomotion this was compatible with the goal of generating propulsion in an efficient manner.     

Study on the Effect of PNF Method on the Flexibility and Strength Quality of Stretching Muscles of Shoulder Joints of Swimmers

In the process of swimming, the shoulder joint will be damaged when the arm is stroking. To reduce the injury of shoulder joints and improve the speed of stroke, it is necessary to train the flexibility of shoulder joints. This paper briefly introduced the concept of shoulder joint and flexibility and then explained the traditional stretching training method and proprioceptive neuromuscular facilitation (PNF) stretching method. Then, taking 20 college team swimmers of Yunnan University as the subjects, the comparative experiment of the traditional and PNF stretching methods was carried out. The results showed that the shoulder rotation index of the athletes after the use of the PNF stretching method was significantly lower compared with the traditional stretching method; under the PNF stretching method, the average power and total work of shoulder joints significantly improved in the high-speed external rotation, and the performance in the 50 m freestyle also significantly improved.     

Inspiratory muscle fatigue after race-paced swimming is not restricted to the front crawl stroke

ABSTRACT: Lomax, M, Iggleden, C, Tourell, A, Castle, S, and Honey, J. Inspiratory muscle fatigue following race-paced swimming is not restricted to the front crawl stroke. J Strength Cond Res 26(10): 2729-2733, 2012-The occurrence of inspiratory muscle fatigue (IMF) has been documented after front crawl (FC) swimming of various distances. Whether IMF occurs after other competitive swimming strokes is not known. The aim of the present study was to assess the impact of all 4 competitive swimming strokes on the occurrence of IMF after race-paced swimming and to determine whether the magnitude of IMF was related to the breathing pattern adopted and hence breathing frequency (fb). Eleven, nationally ranked, youth swimmers completed four 200-m swims (one in each competitive stroke) on separate occasions. The order of the swims, which consisted of FC, backstroke (BK), breaststroke (BR), and butterfly (FLY), was randomized. Maximal inspiratory mouth pressure (MIP) was assessed before (after a swimming and inspiratory muscle warm-up) and after each swim with fb calculated post swim from recorded data. Inspiratory muscle fatigue was evident after each 200-m swim (p < 0.05) but did not differ between the 4 strokes (range 18-21%). No relationship (p > 0.05) was observed between fb and the change in MIP (FC: r = -0.456; BK: r = 0.218; BR: r = 0.218; and FLY: r = 0.312). These results demonstrate that IMF occurs in response to 200-m race-paced swimming in all strokes and that the magnitude of IMF is similar between strokes when breathing is ad libitum occurring no less than 1 breath (inhalation) every third stroke.     

A mechanical supination sprain simulator for studying ankle supination sprain kinematics

This study presents a free-fall mechanical supination sprain simulator for evaluating the ankle joint kinematics during a simulated ankle supination sprain injury. The device allows the foot to be in an anatomical position before the sudden motion, and also allows different degrees of supination, or a combination of inversion and plantarflexion. Five subjects performed simulated supination sprain trials in five different supination angles. Ankle motion was captured by a motion analysis system, and the ankle kinematics were reported in plantarflexion/dorsiflexion, inversion/eversion and internal/external rotation planes. Results showed that all sprain motions were not pure single-plane motions but were accompanied by motion in other two planes, therefore, different degrees of supination were achieved. The presented sprain simulator allows a more comprehensive study of the kinematics of ankle sprain when compared with some previous laboratory research designs.     

Effects of taper on swimming force and swimmer performance after an experimental ten-week training program

The purpose of this research was to examine how an 11-day taper after an 8.5-week experimental training cycle affected lactate levels during maximal exercise, mean force, and performance in training swimmers, independent of shaving, psychological changes, and postcompetition effects. Fourteen competition swimmers with shaved legs and torsos were recruited from the S?o Paulo Aquatic Federation. The training cycle consisted of a basic training period (endurance and quality phases) of 8.5 weeks, with 5,800 m.d(-1) mean training volume and 6 d.wk(-1) frequency; and a taper period (TP) of 1.5 weeks' duration that incorporated a 48% reduction in weekly volume without altering intensity. Attained swimming force (SF) and maximal performance over 200-m maximal swim (Pmax) before and after taper were measured. After taper, SF and Pmax improved 3.6 and 1.6%, respectively (p < 0.05). There were positive correlations (p < 0.05) between SF and Pmax before (r = 0.86) and after (r = 0.83) the taper phase. Peak lactate concentrations after SF were unaltered before (6.79 +/- 1.2 mM) and after (7.15 +/- 1.8 mM) TP. Results showed that TP improved mean swimming velocity, but not in the same proportion as force after taper, suggesting that there are other factors influencing performance in faster swimming.     

Kinematics of the ankle joint complex in snowboarding

Because snowboarders are known to injure their ankles more often than Alpine skiers, it has been postulated that stiffer snowboard boots would provide better protection to the ankle than current soft boots do. Snowboarders are also known to injure their front ankle more often than their back ankle, presumably because of the asymmetrical rotations of the ankles due to asymmetrical binding adjustement. To test these hypotheses, we measured the kinematics of the feet and legs of 5 snowboarders wearing soft boots and stiffer step-in boots during snowboarding maneuvers using an electromagnetic motion tracking system. The results were expressed in anatomically relevant rotations of the ankle joint complex, namely dorsi-/plantar flexion, eversion/inversion, and internal/external rotation. The measured ankle rotations show differences in the movement patterns of the front and back legs. Step-in boots were shown to allow less dorsiflexion, eversion, and external rotation than softer boots, possibly explaining why they are associated with a lower rate of fractures of the talus than soft boots.     

A three-pressure-sensor (3PS) system for monitoring ankle supination torque during sport motions

This study presented a three-pressure-sensor (3PS) system for monitoring ankle supination torque during sport motions. Five male subjects wore a pair of cloth sport shoes and performed 10 trials of walking, running, cutting, vertical jump-landing and stepping-down motions in a random sequence. A pair of pressure insoles (Novel Pedar model W, Germany) was inserted in the shoes for the measurement of plantar pressure at 100Hz. The ankle joint torque was calculated by a standard lower extremity inverse dynamic calculation procedure with the data obtained by a motion capture system (VICON, UK) and a force plate (AMTI, USA), and was presented in a supination/pronation plane with an oblique axis of rotation at the ankle joint. Stepwise linear regression analysis suggested that pressure data at three locations beneath the foot were essential for reconstructing the ankle supination torque. Another group of five male subjects participated in a validation test with the same procedure, but with the pressure insoles replaced by the 3PS system. Estimated ankle supination torque was calculated from the equation developed by the regression analysis. Results suggested that the correlation between the standard and estimated data was high (R=0.938). The overall root mean square error was 6.91Nm, which was about 6% of the peak values recorded in the five sport motions (113Nm). With the good estimation accuracy, tiny size and inexpensive cost, the 3PS system is readily available to be implanted in sport shoe for the estimation and monitoring of ankle supination torque during dynamic sport motions.     

Lower extremity control during turns initiated with and without hip external rotation

The pirouette turn is often initiated in neutral and externally rotated hip positions by dancers. This provides an opportunity to investigate how dancers satisfy the same mechanical objectives at the whole-body level when using different leg kinematics. The purpose of this study was to compare lower extremity control strategies during the turn initiation phase of pirouettes performed with and without hip external rotation. Skilled dancers (n=5) performed pirouette turns with and without hip external rotation. Joint kinetics during turn initiation were determined for both legs using ground reaction forces (GRFs) and segment kinematics. Hip muscle activations were monitored using electromyography. Using probability-based statistical methods, variables were compared across turn conditions as a group and within-dancer. Despite differences in GRFs and impulse generation between turn conditions, at least 90% of each GRF was aligned with the respective leg plane. A majority of the net joint moments at the ankle, knee, and hip acted about an axis perpendicular to the leg plane. However, differences in shank alignment relative to the leg plane affected the distribution of the knee net joint moment when represented with respect to the shank versus the thigh. During the initiation of both turns, most participants used ankle plantar flexor moments, knee extensor moments, flexor and abductor moments at the push leg׳s hip, and extensor and abductor moments at the turn leg׳s hip. Representation of joint kinetics using multiple reference systems assisted in understanding control priorities.     

Dynamic changes of orexin A and leptin in obese children during body weight reduction

In this study, we describe changes of plasma levels of the hypothalamic neuropeptide orexin A in obese children during the reduction of body weight and its relationship to other biochemical and anthropometrical parameters. We measured orexin A fasting plasma levels by the RIA method in 58 obese children--33 girls and 25 boys; mean age 13.1+/-0.38 years (range 7-18.5) before and after 5 weeks of weight-reduction therapy. Leptin, IGF-1, and IGFBP-3 levels were measured in all the subjects and were compared to orexin A levels and anthropometrical data. Average weight in subjects before weight-reduction was 74.2+/-2.79 kg and after weight-loss 67.4+/-2.60 kg (p<0.0001). Orexin A levels before the therapy were 33.3+/-1.97 pg/ml and after the therapy 51.7+/-3.07 pg/ml (p<0.0001). Levels of orexin A were not significantly different between girls and boys (p=0.7842). We found negative correlation between orexin A and age (r = -0.5395; p<0.0001), body height (r = -0.4751; p=0.0002), body weight (r = -0.4030; p=0.0017) and BMI (r = -0.2607; p=0.0481). No correlation was found between orexin A and IGF-1, IGFBP-3 or leptin. Orexin A plasma levels increased during body weight loss, whereas the reverse was true for leptin levels. These findings support the hypothesis that orexin A may be involved in regulation of nutritional status in children.