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Eight cyclists were photographed with a digital camera for three trials while positioned on their own bicycle wearing their helmet. The positions were different from each other and described as hands on the brake hoods, hands below the curve of the brake hoods on the handlebars, and using aerobars. Twenty-four trials were digitized by two different individuals three times to estimate the inter- and intra-rater reliability of the method. The intraclass correlation coefficient (p less than 0.05) value for the intra-rater (test-retest) reliability was 0.993, and for inter-rater consistency, it was 0.976. There were significant differences (p less than 0.05) between digitizers and between trials, apparently due to a learning effect that disappeared by the third trial. Due to small differences between digitizers and trials, caution is recommended when considering the use of this method. (Contains 4 figures.)

The reliability of a laser system was compared with the reliability of a video-based kinematic analysis in measuring displacement and velocity during running. Validity and reliability of the laser on static measures was also assessed at distances between 10 m and 70 m by evaluating the coefficient of variation and intraclass correlation coefficient for each distance. Ten participants completed 3 running trials at self-determined fast, medium, and slow speeds. Running velocity was measured simultaneously by a laser and 2 video cameras (1 at 50 Hz, 1 at 100 Hz) within a 3-m measurement zone (v[subscript zone]). The Root Mean Square errors for static distance measurement using the laser varied with distance, ranging from 4.5 mm at 10 m to 17.8 mm at 70 m. The test-retest reliability of running velocity measurements in the 3-m zone for the 50 Hz and 100 Hz cameras via intraclass correlation were estimated at 0.984 and 0.981, respectively. For the laser, test-retest reliability was estimated at ICC = 0.986. The results of this study indicated that the laser distance measurement device produced valid and reliable estimates of distance. When used within its limitations, the laser system will provide valid and reliable results, which can be made immediately available to the coach, performer, or user without the need to carry out time-consuming digitizing procedures. (Contains 4 figures and 5 tables.)

The purpose of this study was to determine whether there is a linear relationship between the squat and a variety of hamstring resistance training exercises, and whether this relationship differs on the basis of sex. This study also sought to create prediction equations for the determination of hamstring exercise load based on the squat load. Repetition maximums of the squat, as well as 4 common hamstring resistance training exercises including the seated leg curl, stiff leg dead lift, single leg dead lift, and good morning exercise, were determined for each subject. Subjects included 21 men and 13 women collegiate athletes. Data were evaluated using linear regression analysis to predict hamstring exercise loads from 6 repetition maximum squat data. Results of the analysis of all subjects indicated that squat load was a significant predictor of loads for each of the hamstring exercises. However, separate analysis of women revealed that squat load was not a significant predictor of loads for any of the hamstring exercises. Analysis of the men revealed that squat was a significant predictor of load for the seated leg curl ([R.sup.2] = 0.58, p < 0.001), stiff leg dead lift ([R.sup.2] = 0.82, p < 0.001), single leg stiff leg dead lift ([R.sup.2] = 0.80, p < 0.001), and good morning ([R.sup.2] = 0.79, p < 0.001) exercises. On the basis of the analysis of the men, the following prediction equations were devised for each exercise: (1) seated leg curl load = squat load (0.186) + 10.935 kg, (2) stiff leg deadlift load = squat load (1.133) - 86.331 kg, (3) single leg stiff leg deadlift load = squat load (0.443) - 3.425 kg, and (4) good morning load = squat load (0.961) - 105.505 kg. Thus, results from testing core exercises such as the squat can provide useful data for the assignment of loads for assistance exercises. KEY WORDS strength, injury prevention, program design

This study assessed bilateral facilitation and laterality during counter-movement jumps. 23 NCAA Division-I athletes (13 men, 10 women) who participated in track and field volunteered to serve as participants and performed bilateral, right, and left leg countermovement jumps on a force plate. Dependent variables included jump height, reactive strength index, and time to stabilization. A one way analysis of variance showed significant sex differences in single-leg and bilateral jump height and left leg and bilateral reactive strength index. No sex differences were found for time to stabilization. A repeated-measures analysis of variance indicated significant main effects for jump height and reactive strength index but not for time to stabilization. Bonferroni adjusted pairwise comparisons showed that bilateral jump height and reactive strength index values were different from the unilateral conditions. No differences were found between the right and left legs for jump height, reactive strength index, or time to stabilization. Results indicated no evidence of laterality as assessed by jump height, reactive strength index, and time to stabilization. Bilateral facilitation was found as assessed by jump height and reactive strength index. Time to stabilization demonstrated a bilateral deficit phenomenon.

The study assessed the effect of current activation potentiation by evaluating jaw clenching and its effect on the rate of force development (RFD), time to peak force (TTPF). and peak force (PF) during the countermovement jump. Fourteen subjects performed the countermovement jump on a force platform while maximally clenching their jaw on a dental vinyl mouthguard (JAW) as well as without clenching their jaw by jumping with an open mouth (NON-JAW). Results reveal that the RFD was 19.5% greater in the JAW compared with the NON-JAW condition (p < 0.05). The TTPF was 20.15% less in the JAW compared with the NON-JAW condition (p < 0.05). There were no significant differences (p = 0.60) in PF between the JAW and NON-JAW conditions. These findings indicate that concurrent activation potentiation is manifested through jaw clenching during the countermovement jump. As a result, athletes may employ this strategy of maximally clenching their jaws to gain an ergogenic advantage during the countermovement jump. KEY WORDS Jendrassik maneuver, remote voluntary contractions, motor control, plyometrics

The reliability of the reactive strength index (RSI) and time to stabilization (TTS) during maximal-effort plyometric depth jumps was examined. Twenty-two subjects performed three depth jumps from a height of 30 cm. Measures such as height of jump (JH), ground-contact time (CT), RSI, and TTS were obtained and analyzed for reliability using Cronbach alpha reliability coefficient and intraclass correlations. The JH, CT, and RSI were shown to be highly reliable from trial to trial (evidenced by high Cronbach reliability coefficients ([alpha] > 0.95) and high single- and average-measures intraclass correlations (>0.9). Time to stabilization was not reliable from trial to trial, as evidenced by a low Cronbach reliability coefficient ([alpha] < 0.7) and poor single( KEY WORDS plyometrics, balance, stretch shortening cycle

The purpose of this study was to investigate the motor unit activation of the quadriceps (Q), hamstring (H), and gastrocnemius (G) muscle groups during a variety of plyometric exercises to further understand the nature of these exercises. Twenty-four athletes volunteered to perform randomly ordered plyometric exercises, thought to cover a continuum of intensity levels, including two-foot ankle hops; 15-cm cone hops; tuck, pike, and box jumps; one- and two-leg vertical jump and reach; squat jumps with approximately 30% of their 1RM squat load; and 30- and 61-cm depth jumps. Integrated electromyographic data were analyzed for each exercise using a one-way repeated-measures ANOVA. Results revealed significant main effects for the Q when all subjects are analyzed, as well as for separate analysis of men, women, subjects with vertical jumps greater than 50 cm, and those with vertical jumps less than or equal to 50 cm (p [less than or equal to] 0.05). Significant main effects were also found for the G muscle group in the analysis of all subjects, as well as for men and subjects with vertical jumps greater than 50cm (p [less than or equal to] 0.05). No significant main effects were found for the H muscle group. Pairwise comparisons revealed a variety of differences among plyometric exercises. In some cases, plyometrics previously reported to be of high intensity, such as the depth jump, yielded relatively little motor unit recruitment compared with exercises typically thought to be of low intensity. Results can assist the practitioner in creating plyometric programs based on the nature of the motor unit recruitment. KEY WORDS jumping, motor unit recruitment, program design

Complex training research has indicated that 3-4 minutes may be an optimum intracomplex rest interval. The purpose of this study was to determine if a heavy resistive exercise causes performance enhancement of a slow stretch--shortening cycle exercise and if there is an optimal rest interval. Eighteen subjects performed countermovement jumps (CMJs) before and after a 5 repetition maximum back squat lifting protocol. This procedure was repeated 4 times over 2 days using rest intervals of 30 seconds and 2, 4, and 6 minutes. Flight time and peak ground reaction force (GRF) were the dependent variables. All jumps were performed on a specially constructed sledge and force platform apparatus. Repeated measures analysis of variance found a significant reduction in flight time at the 30-second and 6-minute interval (p < 0.05). No significant difference was found between men and women. Only the men showed an enhancement in jump performance after the 4-minute interval. The improvement window was different for each subject, and an analysis of the greatest increase and decrease in flight time and peak GRF was conducted, showing a significant decrease for men and women and a significant increase in flight time for men and peak ground reaction force for women. The results suggest that complex training can benefit or inhibit CMJ performance depending on the rest interval. The individual determination of the intracomplex rest interval may be necessary in the practical setting. Key Words. countermovement jump, stretch--shortening cycle, sledge, resistance exercise, plyometrics

To determine whether creatine monohydrate supplementation would improve performance during a submaximal treadmill run interspersed with high-intensity intervals, 15 college soccer players (8 women, 7 men) received either creatine or a maltodextrin placebo at 0.3 g * kg body mass per day for 6 days. The speed of the treadmill was constant at 160.8 m * min, and every 2 minutes the grade was elevated to 15%. Each hill segment was 1 minute long. At the end of the 20-minute protocol, the treadmill was again elevated to 15% and held there until volitional exhaustion occurred. There was a significant treatment effect of creatine supplementation on body mass (p < 0.05) in the men; however, no significant differences were observed in the women (p > 0.05). There were no treatment effects (p > 0.05) on time to exhaustion, ratings of perceived exertion, or blood lactate concentration. There was a tendency for blood lactate levels to be lower after short-term creatine supplementation in the women, but this was not statistically significant. Based on these results, it appears that creatine supplementation does not improve performance in submaximal running interspersed with high-intensity intervals. Key Words: creatine phosphate, adenosine triphosphate, ergogenic aids, supplementation

Complex training has been recommended as a method of incorporating plyometrics with strength training. Some research suggests that plyometric performance is enhanced when performed 3-4 minutes after the strength training set, whereas other studies have failed to find any complex training advantage when plyometrics are performed immediately after the strength training portion of the complex. The purpose of this study was to determine if there is an ergogenic advantage associated with complex training and if there is an optimal time for performing plyometrics after the strength training set. Subjects were 21 NCAA Division I athletes who performed a countermovement vertical jump, a set of 5 repetitions maximum (5RM) squats, and 5 trials of countermovement vertical jump at intervals of 10 seconds and 1, 2, 3, and 4 minutes after the squat. Jump height and peak ground reaction forces were acquired via a force platform. The pre-squat jump performance was compared with the post-squat jumps. Repeated measures ANOVA determined a difference (p [less than or equal to] 0.05) between genders and that jump performance immediately following the squat exercise was hindered (0.66 m), but no effect (p > 0.05) was found comparing subsequent jumps (0.72-0.76 m) to the pre-squat condition (0.74 m). When comparing high to low strength individuals, there was no effect on jump performance following the squat (p > 0.05). In conclusion, complex training does not appear to enhance jumping performance significantly and actually decreases it when the jump is performed immediately following the strength training set; however, a nonsignificant trend toward improvement seemed to be present. Therefore to optimize jump performance it appears that athletes should not perform jumps immediately following resistance training. It may be possible that beyond 4 minutes of recovery performance could be enhanced; however, that was not within the scope of the current study. Key Words: contrast training, power, plyometrics

This study examined mean integrated electromyography (I-EMG) for the quadriceps and hamstring muscle groups, as well as mean and peak vertical ground reaction forces (GRFs), for 3 conditions of the back squat. Conditions included (a) squat with barbell and weight plates, (b) squat with barbell and weight plates plus chains hung on each end of the barbell to replace approximately 10% of the squat load, and (c) squat with barbell and weight plates plus elastic bands offering resistance equivalent to approximately 10% of the squat load. Weight plates equal to the load added by either the chains or elastic bands were removed for the latter 2 squat conditions. Vertical GRFs were obtained during a single testing session for all 3 squat conditions. The tests were performed on a 2-cm thick aluminum platform (0.76 x 1.0 m) bolted directly to a force plate (OR6-5-2000, AMTI, Watertown, MA). Surface electrode I-EMG data from the quadriceps and hamstrings were recorded at 500 Hz. The exercise order was randomly determined for 11 NCAA Division I athletes who had experience using these types of squats. A repeated measures analysis of covariance revealed no differences in I-EMG and GRF during the eccentric or concentric phase for any of the 3 squat conditions. Analyses showed that mean GRF and I-EMG was significantly different between eccentric and concentric phases for all groups. The results question the usefulness of performing squats combining barbell and weight plates with chain and elastic resistance. Key Words: compensatory resistance, strength, back squat

Rock climbers believe chalk dries the hands of sweat and improves the static coefficient of friction between the hands and the surface of the rock. The purpose of this study was to assess whether chalk affects geometric entropy or muscular activity during rock climbing. Nineteen experienced recreational rock climbers (13 males, 6 females; 173.5 ± 7.0 cm; 67.5 ± 3.4 kg) completed 2 climbing trails with and without chalk. The body position of the climber and muscular activity of the finger flexors was recorded throughout the trial. Following the movement sequence participants hung from a standard climbing hold until they slipped from the climbing structure, while the coefficient of friction and the ratio of the vertical forces on the hands and feet were determined. Although there were no differences in the coefficient of friction (P = .748), geometric entropy (P - .359), the ratio of the vertical forces between the hands and feet (P = .570), or muscular activity (P = .968), participants were able to hang longer after the use of chalk 62.9 ± 36.7 s and 49.3 ± 25.2 s (P = .046). This is advantageous because it may allow for prolonged rests, and more time to plan the next series of climbing moves. [ABSTRACT FROM AUTHOR]

Lower geometric entropy (GE) could represent more economical movement in rock climbing. Repetition of a climbing route decreases energy expenditure (EE), however, association with changes in GE has not been studied. The purpose of this study was to observe changes in GE with repetition of a climbing route relative to changes in EE. Nine climbers completed nine ascents each, one week apart, on an indoor climbing structure. Digital video was recorded at 30 Hz and a marker point was digitised as an estimate of a climber's centre of mass position (CME). The displacement of CME was expressed as the length of the line of motion (LM). GE was calculated as ln((2 x LM)/CH)) where CH is the value of the convex hull about the LM. Indirect energy expenditure (EECLM) was calculated from expired air by the Weir method. Data were analysed for ascents 1 (A1), 3 (A3), 6 (A6) and 9 (A9) and compared via repeated measures ANOVA. GE was significantly different for A1 vs A6 and A9 (p < 0.05) and not different for other comparisons. GE was correlated with EECLM; r = 0.67 (p < 0.01). Climbers reduce geometric entropy with route familiarity and the lower entropy may be associated with lower energy expenditure. [ABSTRACT FROM AUTHOR]

Various publications discuss the discrepancies of running in triathlons and stand-alone runs. However, those methods, such as analysing step-characteristics or ground-contact time, lack the ability to quantitatively discriminate between subtle running differences. The attractor method can be applied to overcome those shortcomings. The purpose was to detect differences in athletes' running patterns (δM) and movement precision (δD) by comparing a 5,000 m run after a prior cycling session (TRun) with an isolated run over the same distance (IRun). Participants completed the conditions on a track and a stationary trainer, allowing the use of their personal bike to simulate an Olympic triathlon. During each run, three-dimensional acceleration data, using sensors attached to the ankles, were collected. Results showed that both conditions lead to elevated attractor parameters (δM and δD) over the initial five minutes before the athletes found their rhythm. This generates a new perspective because independent of running after a bike session or without preload, an athlete needs certain time to adjust to the running movement. Coaches must consider this factor as another tool to fine-tune pacing and performance. Moreover, the attractor method is a novel approach to gain deeper insight into human cyclic motions in athletic contexts. [ABSTRACT FROM AUTHOR]