The effect of a resistance training programme on the grab, track and swing starts in swimming

Transcription

1 Journal of Sports Sciences, 2003, 21, The effect of a resistance training programme on the grab, track and swing starts in swimming RAY V.P. BREED* and WARREN B. YOUNG Department of Human Movement and Sport Sciences, University of Ballarat, PO Box 663, Ballarat, Victoria 3350, Australia Accepted 20 December 2002 The aim of this study was to establish the effectiveness of a resistance training programme, designed to improve vertical jumping ability, on the grab, swing and rear-weighted track starts in swimming. Twenty-three female non-competitive swimmers participated (age years; mean+s). The diving techniques were practised weekly for 8 weeks. The participants were randomly assigned to a control group (n = 11) or a resistance-training group (n = 12), which trained three times a week for 9 weeks. The tests before and after the training programme involved performing each dive technique and six dry-land tests: two countermovement jumps (with and without arms), two isokinetic squats (bar speeds of 0.44 and 0.70 rad s 71 ) and two overhead throws (with and without back extension). A repeated-measures multivariate analysis of variance was used to show that resistance training improved performance in the dry-land tests (P ). No significant improvements due to training were found for any temporal, kinematic or kinetic variables within the grab or swing starts. Significant improvements (P 50.05) were found for the track start for take-off velocity, take-off angle and horizontal impulse. The results suggest that the improved skill of vertical jumping was not transferred directly to the start, particularly in the grab technique. Non-significant trends towards improvement were observed within all starts for vertical force components, suggesting the need to practise the dives to retrain the changed neuromuscular properties. Keywords: diving, force, power, speed, vertical jump. Introduction An effective start is an essential part of competitive swimming, particularly in the shorter sprint races. To produce a fast entry, the take-off velocity must be high and then a streamlined position underwater should be maintained to minimize the loss of horizontal velocity (Guimaraes and Hay, 1985). Maglischo (1993) stated that the three requirements for a good start are a fast reaction time, great jumping power and a low resistance during underwater gliding. Although little can be done to improve reaction time, the other two factors can be improved by training. Some researchers have shown a significant positive correlation between vertical jumping ability and starting performance (Zatsiorsky et al., 1979; Pearson et al., 1998). Thus, greater muscular leg power and improved jumping ability may be important in reducing the starting time and, consequently, overall race time (Lyttle and Ostrowski, 1994). * Author to whom all correspondence should be addressed. r.breed@ballarat.edu.au Adams (1986) maintained that lower body power is essential for fast starts and turns in swimming. However, research has been limited on lower limb leg strength and power in relation to swimming start performance. Miyashita et al. (1992) found a statistically significant correlation (P 50.05) between leg extensor power and flight distance (r = 0.76) and performance to 5 m (r = 70.68). Some researchers have reported a significant correlation between standing vertical jump and starting performance over a criterion distance (Zatsiorsky et al., 1979; Counsilman, 1986; Pearson et al., 1998). Counsilman (1986) also suggested that vertical jump performance is an indicator of the power that could be produced by the rest of the body, including the arms, which provide most of the propulsion in the freestyle stroke. Although relationships have been observed in descriptive research, no experimental research has determined if training to increase vertical jumping improves starting performance. The contributions of the arms and of the trunk in the vertical jump can help to increase the amount of preload in the leg extensor muscles. Therefore, as a Journal of Sports Sciences ISSN print/issn X online # 2003 Taylor & Francis Ltd DOI: /

2 214 Breed and Young result of pre-stretching during the preparatory phase, the leg extensor muscles can better utilize the higher force attained at the end of the stretch (Walshe et al., 1998). Shierman (1979) found that the shape of the force curve for the gathering phase of the dive start was similar to the shape of other vertical force curves elicited when performing dynamic movements such as the vertical jump. Research has found that the arms contribute 10 15% of the height obtained in the vertical jump (Khalid et al., 1989; Harman et al., 1990; Lees and Barton, 1996). Through the use of modified vertical jumps, Luhtanen and Komi (1978) examined the segmental contributions to vertical jump performance and found that knee extension, plantar flexion, trunk extension, arm swing and head swing contributed 56, 22, 10, 10 and 2%, respectively. However, Robertson and Stewart (1998) found that the contribution of the trunk segment was much higher (36.5% of the total work) during the grab start in swimming than during a vertical jump because of greater hip flexion. Robertson and Stewart (1998) also found similarities in the movement pattern of the vertical jump and the grab start, in that both techniques involved the muscle groups contributing simultaneously rather than sequentially to the total work done. This observation suggests that training to improve vertical jumping ability might enhance grab start performance. There is a need for more research to establish the relative usefulness of land-based leg power training to starting performance, to establish the value of including leg power exercises in swimmers training programmes. The grab and track starts are common techniques in swimming races, whereas the swing start is widely used during relay changeovers (Breed and McElroy, 2000). All three starts have different starting mechanisms; thus resistance training might have a different effect on each. For example, since the swing start involves a pronounced arm swing, it is conceivable that this technique might benefit more than the other techniques from training that targets the muscles producing the arm swing. The aim of the current study was to determine if a resistance training programme designed to increase vertical jumping ability could enhance various performance parameters in the grab, swing and track starts. Methods Participants Twenty-three female students, studying physical education/human movement courses, from the University of Ballarat volunteered to participate in the study. The mean age of the students was 18.9 years (s = 1.5); their mean height and mass were 1.66 m (s = 0.07) and 64.9 kg (s = 5.2), respectively. The participants were all athletes from a range of sporting disciplines other than competitive swimming. This was considered important, as it was necessary for all participants to acquire equal standards of the techniques in each of the starts to minimize performance bias. Procedures and equipment Dive technique training The participants were taught the techniques of three dives: the grab, swing and rear-weighted track starts (see Breed and McElroy, 2000). After an initial learning phase, the participants practised by performing ten dives of each technique for one supervised session a week over 8 weeks. The participants were videotaped during weeks 2 and 5 of training to assist with learning and feedback. Test protocols The test sessions before and after the training programme consisted of two parts: (1) six dry-land tests of strength, power and jumping ability and (2) the performance of three dive start techniques. The test protocols were identical before and after the training programme. Dry-land testing was performed 5 days after the resistance training programme with the dive start tests 2 days later. After the pre-test, the participants were allocated at random to a control group (n = 11) or a resistance training group (n = 12). The two groups continued with their normal daily activities; the resistance training group also participated in a 9-week training programme designed to enhance jumping ability. Dry-land testing Six tests of muscle function were included in this study, two vertical jumping tests, two overhead throws and two one-repetition maximum (1-RM) squat exercises. The tests and the main qualities assessed are listed in Table 1 to help justify the inclusion of the tests. The six tests were:. Countermovement jumps with and without arm swing. For the countermovement jump with arm swing, a Yardstick device (Swift Equipment, Lismore, NSW) was used to measure the height of the jump to the nearest centimetre. A standing double foot take-off with a countermovement and arm swing was adopted. For the countermovement jump without arm swing, a cm contact mat (Young et al., 1995) linked to a computer was used so that jump height could be recorded and calculated from the flight time. Hands were placed

3 Effect of resistance training on swim starts 215 Table 1. Dry-land tests and the quality assessed Test Countermovement jump with arm swing Countermovement jump without arm swing Overhead throw without back extension Overhead throw with back extension Squat jump at 0.70 rad s 71 Squat jump at 0.44 rad s 71 Quality assessed Standing vertical jumping ability Leg extensor power, specific to standing vertical jump Shoulder power Back extensor and shoulder power Leg extensor power, no jumping skill required Leg extensor strength on hips and the participants were instructed to maintain the same body position when landing as during the take-off (i.e. hip, knees and ankles in an extended position).. Overhead throws with and without back extension. A 2.73 kg metal shot, covered in magnesium chalk powder, was thrown onto gymnastic tumbling mats. The participants sat with their back facing the direction of the throw, heels placed against the front legs of the chair and holding the shot with both hands. In the overhead throw without back extension, the back was pressed against the chair upright with the arms extended and forearms resting on the thighs. In the overhead throw with back extension, the hands rested on the ground between the feet. The participants were instructed to throw the shot over their head for maximum distance while keeping their arms straight. Using a tape measure, the distance was calculated to the lowest whole centimetre by measuring from the back chair legs to the nearest landing point. The trial was repeated if there was any initial countermovement.. Squat jumps at 0.44 and 0.70 rad s 71. An Ariel 5000 Computerized Exercise System (CES) was used to measure peak isokinetic strength and peak power during a squat at bar angular velocities of 0.44 and 0.70 rad s 71, respectively (Ashley and Weiss, 1994). The participants lowered the bar slowly until 908 knee flexion had been reached, then held this position for s before reacting to a verbal go signal by extending the legs as fast as possible and finishing on the toes. A time delay was imposed to remove most of the stretch shorten cycle effect (Wilson et al., 1991) and make the test one of predominantly concentric muscle function. A standardized warm-up consisting of running and stretching was performed, followed by the randomly ordered tests. The participants practised before each of the six tests until they were confident and produced good, consistent techniques. A rest of 3 min was allowed between tests. Three trials were performed for each test with 30 s rest between each, with the best performance of the three trials being used for analysis. Dive testing After a warm-up, which consisted of 5 min of light swimming in the pool and three practice trials of each technique, the participants were videotaped performing two trials of each diving technique in random order. A video recorder (Panasonic MS-5) was positioned sagittal to the plane of the dive. Eleven anatomical points were marked so that centre of mass calculations could be made through digitizing. Dives were performed on a modified starting block mounted with a m waterproof Kistler force plate. Left and right load cells were attached to a hand bar mounted at the front of the block to allow hand forces to be measured separately from the feet during the grab and track starts (see Breed and McElroy, 2000). Nine dive performance variables were selected for statistical analysis between the grab, track and swing starts. An average of the two trials for each variable was used for analysis. These variables included the block time, flight time, total time to entry, flight distance, resultant take-off velocity, take-off angle, entry angle, net vertical impulse and total horizontal impulse. Hand forces were also measured and compared between the grab and track starts. Flight distance was used as an indicator of dive performance for correlation with the dry-land tests. No underwater measure was performed, as we believed that novice swimmers could have too much variation between trials. Resistance training All participants had some experience and knowledge of resistance training, but none had previously used strength training programmes specific to their chosen sport. Three training sessions per week were performed for 9 weeks; participants were excluded from analysis if more than four sessions were missed. The main aim of the programme was to enhance vertical jumping performance. The programme was periodized initially

4 216 Breed and Young to improve strength and power, with more specific exercises for vertical jumping being included in the latter part of the programme while maintaining general lower and upper body strength and power (see Table 2). The main muscle groups used in vertical jumping were trained, which included the knee extensors, lower trunk and shoulders (Luhtanen and Komi, 1978; Khalid et al., 1989). Statistical analysis Pearson s correlation coefficients were calculated for the pre-test variables to identify any relationship between jumping ability and dive performance. A 262 (group by time) repeated-measures (dry-land tests) multivariate analysis of variance (MANOVA) was conducted to establish if there was a training effect. Nine separate 262 (group by time) repeated-measures (dive technique) MANOVA tests were conducted across each diving technique for all dependent dive start variables at a 95% level of confidence. Results We addressed three questions. First, is vertical jumping ability related to the three dive techniques? Second, would resistance training improve vertical jumping ability and other tests of muscle function? Third, would aspects of diving performance of the three starting techniques improve after training? Correlation coefficients between the countermovement jump with arm swing, countermovement jump without arm swing and flight distance for all three diving techniques before training are presented in Fig. 1. The flight distances of all three dives were significantly correlated with both jumping tests (P 50.01), but not with either of the isokinetic squat tests (P 40.05). The results indicated that resistance training improved performance in the dry-land tests (F = 10.3, P ). Univariate analyses showed a significant group by time effect for the countermovement jump with arm swing, countermovement jump without arm swing and squat jump test at 0.70 rad s 71. The results and percentage changes for both groups in each dryland test are presented in Table 3. The significant dive start variables are presented in Table 4. No significant group by time differences were found for any variable within the grab or swing starts (P 40.05). There were no significant group by time differences in any temporal variable for each of the three techniques (P 40.05). A significant group by time effect was found within the track start for total horizontal impulse (P 50.05), an increase that was most probably due to the significant improvement of hand impulse (P 50.01). Table 2. Nine-week resistance training programme Sessions 1 and 3 Sets6reps (load) Session 2 Sets6reps (load) Weeks 1 3 Clean pull 465 (8-RM)* Barbell jump squat 565 (10 15 kg) Barbell press (behind neck) 368 (10-RM) Back extension Parallel squat (Smith mach) 368 (10-RM) Prone hold s Back extension Prone hold s Weeks 4 6 Barbell jump squat 464 (15 20 kg) Weighted belt jump 565 (9 kg) Dumbbell overhead press 466 (6-RM) Back extension 268 (5 10 kg) Barbell half squat 466 (6-RM) Twisting crunch 26max Back extension 268 (5 10 kg) Twisting crunch 26max Weeks 7 9 Drop jump 565 (45 60 cm) Barbell half squat 465 (5-RM) Cable arm drive 565 (8-RM) Barbell jump squat 465 (17 25 kg) Weighted belt jump 565 ( kg) Dumbbell arm drive 565 (5-RM) Side hold 36max * RM = the maximum load attainable for the repetitions stated.

5 Effect of resistance training on swim starts CMJ with Discussion 0.74** 0.69** 0.84** FD grab FD track FD swing 0.71** 0.60* 0.63* 0.65* CMJ without Fig. 1. Relationship between countermovement jumps and flight distance. CMJ with = countermovement jump with arm swing, CMJ without = countermovement jump without arm swing, FD = flight distance. *P 50.01, **P Table 3. Descriptive data for the dry-land tests before and after the training programme (mean+s) Test Control group Resistance-trained group CMJ with arm swing (cm) Before After % change ** CMJ without arm swing (cm) Before After % change ** Squat jump at 0.70 rad s 71 (kg) Before After % change * Squat jump at 0.44 rad s 71 (kg) Before After % change Abbreviation: CMJ = countermovement jump. *P 50.05, **P Relationship between dry-land tests and dive performance During a vertical jump, the muscle groups are recruited simultaneously rather than sequentially (Hudson, 1986; Lees and Barton, 1996). Robertson and Stewart (1998) reported a similar contribution of joint moments and coordination patterns for the grab start in swimming. Both the vertical jump and swim starts include complex 217 actions involving the ankle, knee, hip, elbow and shoulder joints. In the present study, both countermovement jumps were significantly correlated with the flight distance of all three techniques (P 50.05). These results suggest the possibility of a commonality between vertical jumping and diving (Lyttle and Ostrowski, 1994; Pearson et al., 1998; Robertson and Stewart, 1998). The isokinetic squat tests of power (0.70 rad s 71 ) and strength (0.44 rad s 71 ) were not significantly correlated with flight distance for any start technique (P ). This could be because isokinetic testing is non-specific to the accelerative nature of the dive start, and that the squat tests measured only concentric muscle function. This is in contrast to the pre-loading or stretch shorten cycle of the muscles that occurs during the jumping tests and dive starting. Also, diving involves more skill than the squat tests, as it requires greater muscle coordination and finding an optimal take-off angle combined with forward rotation of the body. Dry-land tests There was a significant group by time interaction of resistance training (P ), resulting in improved performance in the dry-land tests. Performance improved due to the training in three of the six tests (countermovement jump with and without arm swing, squat jump at 0.70 rad s 71 ) (see Table 3). The 5.3 cm (12.3%) increase in height of the countermovement jump with arm swing for the training group was similar to the increases reported by Bauer et al. (1990), Holcomb et al. (1996) and Lyttle et al. (1996), all of whom trained male participants for 8 10 weeks. The two overhead throw tests were not improved by training. As these tests involved a high amount of skill and a relatively unfamiliar movement pattern for the participants, they might not have been sensitive to training improvements of the upper body. It is also possible that variations in the angle of release influenced the results. In contrast, the two countermovement jump tests were quite specific to many movement patterns involved in the training exercises (i.e. jump squats, weighted jumps). Dive start performance Flight distance is a very important performance variable in dive starting, particularly as the body can travel considerably faster through the air than in water (Miller et al., 1984; Robertson and Stewart, 1998). Resistance training did not improve the flight distance of any starting technique (P 40.05). This finding was unexpected, as vertical jumping ability, which improved

6 218 Breed and Young Table 4. Dive start variables before and after the training programme (mean+s) Start Control group Resistance-trained group Velocity (m s 71 ) Grab start Before After % change Track start Before After % change * Swing start Before After % change Take-off angle (8) Grab start Before After % change Track start Before After % change ** Swing start Before After % change Total horizontal impulse (N s) Grab start Before After % change Track start Before After % change * Swing start Before After % change Horizontal impulse of hands (N s) Grab start Before After % change Track start Before After % change ** *P 50.05, **P after training, was significantly correlated (P 50.01) with flight distance in all three techniques. This would suggest that improvements in jumping ability were not transferred directly to the skill of diving. Even though similarities exist in the timing and muscle segmental contributions of the vertical jump and grab start (Shierman, 1979; Robertson and Stewart, 1998), improvements in jumping ability might not be observed in dive performance due to the extra skill involved in starting. For example, dive starting requires changes in body position during flight and the need to find an optimal take-off angle for maximum performance. The small number of participants in each group (control, n = 11; experimental, n=12) might have reduced the possibility of reaching significance. As the partial etasquared value of 0.13 indicated a moderate to large effect size (Cohen, 1988), non-significant trends will also be discussed. When comparing the control and experimental groups, a trend towards non-significant improvements in flight distance was found for the track and swing starts, with no change for the grab start. Similar values were found for both resultant take-off velocity and flight distance, confirming that take-off velocity is the main determinant of a projectile s range. The resultant takeoff velocity of the track start increased significantly (P 50.05) after training. No temporal variable changed after training (P 40.05). Kinetic analyses showed that improvements (P 50.05) due to training were transferred only to the track start in the horizontal direction of force production. Horizontal impulse was broken down into foot and hand impulse for the grab and track starts and analysed separately. No improvements in foot horizontal impulse were found for either start. However, the hand horizontal impulse of the track start increased by about 30% (P 50.01) after training, which would explain the significant improvements in total horizontal impulse and resultant take-off velocity. This further shows that the arms have a large role in providing horizontal momentum of the body in the rear-weighted track start, particularly during the early part of the movement. As vertical velocity of the centre of gravity at take-off determines the height of a vertical jump (Oddson, 1989), it is logical that an improvement in vertical jump performance could lead to an increase in resultant takeoff velocity in a dive start. However, much smaller increases in resultant take-off velocity were seen after training compared with jump height. When the force data for the dives were analysed, a non-significant trend showed that training might have improved the vertical impulse in all three starts. This finding would help to account for the increased take-off angles of the starts, particularly in the track technique. When the hands were analysed separately, an improvement in hand vertical

7 Effect of resistance training on swim starts 219 impulse was noted in the track and grab starts after training. This might further support the concept that the role of the arms in the vertical direction is to pre-tense the leg extensors and increase the loading of the leg muscles (Cavanagh et al., 1975; Guimaraes and Hay, 1985). The improvements in vertical force components for all starts suggest that the improved skill of jumping was not transferred directly to the start, particularly in the grab technique, which showed no improvements in flight distance or resultant take-off velocity. No significant results or trends were observed for the entry angle of any start due to training. Although a similar trend was found for all starts, in that take-off angle increased after resistance training, only the track start increased significantly (P 50.01). This would also help to account for the increase in flight distance. The higher take-off angle could have been due to an increase in vertical velocity during the start, also responsible for improved vertical jump performance. An increase in vertical velocity, and hence take-off angle, might indicate a need for practising the dives to retrain the changed neuromuscular properties due to the resistance training. Bobbert and Van Soest (1994) used a model to simulate vertical jump squats. When the input data were increased (representing greater strength) and timing remained the same, jump height decreased. This is a possible explanation for the very small improvements in diving performance when compared to the increases in vertical jump height. Therefore, it is possible that larger improvements would have been observed in aspects of dive performance if the participants had practised the dives throughout the resistance training period, so as to adapt the timing of the neuromuscular system to account for the increased muscle force capability. A possible reason for the minimal skill transfer from resistance training to diving could be the slower speed of muscular contraction, particularly during the eccentric phase of the dive (Harman et al., 1990). This slower contraction speed is needed to allow for forward rotation of the body to move into its line of push. Training effects for the track start might be greater than those for either the grab or swing start, as the track start uses a different mechanism for starting, with the body being pulled directly forwards rather than dipping or lowering the body s centre of mass (Breed and McElroy, 2000). The improvement of the track start is probably due to the large increase in total horizontal impulse of the arm pull, rather than improved jumping ability. Conclusions Jumping ability was significantly correlated to the flight distance of all three starting techniques (P 50.01). The resistance training programme significantly improved leg power and jumping ability. The results indicated that improved jumping ability increased the vertical force components of all three starting techniques. However, no significant improvements in flight distance were found for any start, suggesting that there was no direct transfer of skill to the swim starts. This finding further supports the need to adapt the control mechanisms of the diving techniques by practising them during resistance training (Bobbert and Van Soest, 1994). It is recommended that swimmers experiment with different start types to find their preferred technique. The swimmer s preferred dive technique should be practised throughout resistance training to re-optimize the skill and control mechanisms of the neuromuscular system. Testing should also be performed throughout training so that it can be monitored when a plateau is reached in both dry-land and diving skills. References Adams, T. (1986). Jumping into strength training. Swimming Technique, January, pp Ashley, C.D. and Weiss, L.W. (1994). Vertical jump performance and selected physiological characteristics of women. Journal of Strength and Conditioning Research, 8, Bauer, T., Thayer, R.E. and Baras, G. (1990). Comparison of training modalities for power development in the lower extremity. Journal of Applied Sport Science Research, 4, Bobbert, M.F. and Van Soest, A.J. (1994). Effects of muscle strengthening on vertical jump height: a simulation study. Medicine and Science in Sports and Exercise, 26, Breed, R.V.P. and McElroy, G.K. (2000). A biomechanical comparison of the grab, swing and track starts in swimming. Journal of Human Movement Studies, 39, Cavanagh, P., Palmgren, J. and Kerr, B. (1975). A device to measure forces at the hands during the grab start. In Swimming II, International Series on Sport Science (edited by L. Lewillie and J.P. Clarys), pp Baltimore, MD: University Park Press. Cohen, J. (1988). Statistical Power Analysis for the Behavioural Sciences. Hillsdale, NJ: Erlbaum. Counsilman, J.E. (1986). The importance of power. Swimming Times, February, pp Guimaraes, A.C.S. and Hay, J.G. (1985). A mechanical analysis of the grab starting technique in swimming. International Journal of Sport Biomechanics, 1, Harman, E.A., Rosenstein, M.T., Frykman, P.N. and Rosenstein, R.M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22, Holcomb, W.R., Lander, J.E., Rutland, R.M. and Wilson, G.D. (1996). The effectiveness of a modified plyometric program on power and the vertical jump. Journal of Strength and Conditioning Research, 10,

8 220 Breed and Young Hudson, J.L. (1986). Coordination of segments in the vertical jump. Medicine and Science in Sports and Exercise, 18, Khalid, W., Amin, M. and Bober, T. (1989). The influence of the upper extremities movement on take-off in vertical jump. In Biomechanics in Sports V (edited by L. Tsarouchas, J. Terauds, B.A. Gowitzke and L.E. Holt), pp Athens: Hellenic Sports Research Institute. Lees, A. and Barton, G. (1996). The interpretation of relative momentum data to assess the contribution of the free limbs to the generation of vertical velocity in sports activities. Journal of Sports Sciences, 14, Luhtanen, P. and Komi, P.V. (1978). Segmental contribution to forces in vertical jump. European Journal of Applied Physiology, 38, Lyttle, A. and Ostrowski, K. (1994). The principles of power development for freestyle sprints. Strength and Conditioning Coach, 2(4), Lyttle, A.D., Wilson, G.D. and Ostrowski, K.J. (1996). Enhancing performance: maximal power versus combined weights and plyometrics training. Journal of Strength and Conditioning Research, 10, Maglischo, E.W. (1993). Swimming Even Faster. Mountain View, CA: Mayfield Publishing. Miller, J.A., Hay, J.G. and Wilson, B.D. (1984). Starting techniques of elite swimmers. Journal of Sports Sciences, 2, Miyashita, M., Takahashi, S., Troup, J.P. and Wakayoshi, K. (1992). Leg extension power of elite swimmers. In Biomechanics and Medicine in Swimming: Swimming Science VI (edited by D. MacLaren, T. Reilly and A. Lees), pp London: E & FN Spon. Oddson, L. (1989). What factors determine vertical jumping height? In Biomechanics in Sports V (edited by L Tsarouchas, J. Terauds, B.A. Gowitzke and L.E. Holt), pp Athens: Hellenic Sports Research Institute. Pearson, C.T., McElroy, G.K., Blitvich, J.D., Subic, A. and Blanksby, B.A. (1998). A comparison of the swimming start using traditional and modified starting blocks. Journal of Human Movement Studies, 34, Robertson, D.G.E. and Stewart, V.L. (1998). Power production during swim starting. Communication to the Sixteenth Congress of Biomechanics and Medicine in Swimming, Jyväskylä, Finland, 28 June 2 July. Shierman, G. (1979). The grab and conventional swimming starts: a force analysis. Journal of Sports Medicine and Physical Fitness, 19, Walshe, A.D., Wilson, G.J. and Ettema, G.J. (1998). Stretch shorten cycle compared with isometric preload: contributions to enhanced muscular performance. Journal of Applied Physiology, 84, Wilson, G.J., Elliot, B.C. and Wood, G.A. (1991). The effect on performance of imposing a delay during a stretch shorten cycle movement. Medicine and Science in Sports and Exercise, 23, Young, W.B., Pryor, J.F. and Wilson, G.J. (1995). Effect of instructions on characteristics of countermovement and drop jump performance. Journal of Strength and Conditioning Association, 9, Zatsiorsky, V.M., Bulgakova, N.Z. and Chaplinsky, N.M. (1979). Biomechanical analysis of starting techniques in swimming. In Swimming III: Proceedings of the Third International Symposium of Biomechanics in Swimming, pp Edmonton, Alberta: University of Alberta.

9