What the experts say
Nigel Hetherington reviews the latest research material relating to coaching, exercise physiology and athletic development.
The mastery approach to coaching is a cognitive-behavioural intervention designed to promote a mastery-involving motivational climate shown to be related to lower anxiety in athletes. Researchers tested the effects of this intervention on motivational climate and on changes in male and female athletes' cognitive and somatic performance anxiety over the course of a basketball season. Results revealed that the athletes in the intervention condition perceived their coaches as being more mastery-involving on the Motivational Climate Scale for Youth Sports when compared to athletes in an untreated control condition. Relative to athletes who played for untrained coaches, those who played for the trained coaches exhibited decreases in sport anxiety and on total anxiety scores from preseason to late season. Control group athletes reported increases in anxiety over the season. The intervention had equally positive effects on boys and girls teams.
A study addressed the question, what should baseball players focus their attention on while batting? Less-skilled and highly skilled baseball players participated in four dual-task conditions in a baseball batting simulation: two that directed attention to skill execution - movement of the hands and movement of the bat and two that directed attention to the environment - auditory tones and the ball leaving the bat. Batting performance for highly skilled players was best in the ball leaving the bat condition and worst in the skill execution condition. Performance of less-skilled batters was significantly better in the two skill conditions than in either of the two environmental conditions. This finding supports the importance of a skill becoming subconscious for best execution with a skilled player and conscious for a less-skilled player.
Previous findings of time-of-day differences in athletic performance could be affected by daily fluctuations in environmental and behavioural 'masking' factors (e.g., sleep, ambient temperature, and energy intake). A study examined whether there is a circadian rhythm in swim performance independent of these masking factors. 25 experienced swimmers were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3 hour "ultra-short" sleep-wake cycle, involving 1 hour of sleep in darkness and 2 hour of wakefulness in dim light repeated throughout the observation. The protocol distributes the 'masking' factors equally across the 24 hour period. Each swimmer performed six maximal-effort 200-metre swim trials distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 hours. Intra-aural temperature was used to find the lowest body temperature (Tmin). Swim performances were compared across the eight times of day and across twelve 2-hour intervals relative to Tmin. A significant pattern was found in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 hours before Tmin ( 2300) and was worst from 1 hour before to 1 hour after Tmin ( 0500). Mean swim performance was 169.5 seconds; circadian variation from peak to worst performance was 5.8 seconds. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioural masking effects.
A review aimed to determine the prevalence and predictors of preseason conditioning among 451 high school athletes participating in girls and boys track and boys soccer teams. The main outcome measure was meeting criteria for adequate preseason conditioning through a combination a minimum of 300 min/week of aerobic conditioning and stretching and strengthening exercises (at least three times a week for any duration). The majority of athletes met the criteria for each of the components (59% for aerobic conditioning, 62% for stretching, 63% for strengthening). 33% met the criteria for all three components of which the majority reported at least 1 month of conditioning to prepare for the season. Athletes who reported help with conditioning from a coach were twice as likely to have adequate preseason conditioning compared with those who did not receive help from a coach (45 vs. 23%). These findings highlight the need for school- or coach-sponsored involvement to ensure that all athletes engage in comprehensive preseason conditioning programs.
Researchers investigated muscle deoxygenation and neural drive-related changes during repeated cycling sprints in a fatiguing contex. Nine healthy male subjects performed a repeated-sprint test (consisting of 10 x 6-s maximal sprints with 30s of recovery). Oxygen uptake was measured breath-by-breath; muscle deoxygenation of the vastus lateralis was assessed continuously. Results showed a significant power decrement during repeated-sprint exercise. There was also a progressive muscle deoxygenation, but the ability of the subjects to use available oxygen throughout the entire repeated-sprint test was well preserved. A significant decrease in muscle activity and motor drive was also measured during the acceleration phase of each sprint across the repeated-sprint exercise. The findings suggest that the ability to repeat short-duration (6s) sprints with 30s recoveries was associated with the occurrence of both peripheral and central fatigue.
The influence of various loads on power output in the jump squat (JS), squat (S), and power clean (PC) was examined to determine the load that maximizes power output in each lift. Twelve male athletes participated in four testing sessions. The first session involved performing one-repetition maximums (1RM) in the S and PC, followed by three randomized testing sessions involving the JS, S, or PC. Peak force, velocity, and power were calculated across loads of 0, 12, 27, 42, 56, 71, and 85% of each subject's 1RM in the JS and S and at 10% intervals from 30 to 90% of each subject's 1RM in the PC.
The optimal load for the JS was 0% of 1RM; absolute peak power and peak power were significantly lower from the optimal load across the loading spectrum. Peak power in the S was maximized at 56% of 1RM; however, power was not significantly different across the loading spectrum. The optimal load in the PC occurred at 80% of 1RM. Relative peak power at 80% of 1RM was significantly different from the 30 and 40% of 1RM.
This investigation indicates that the optimal load for maximal power output occurs at various percentages of 1RM in the JS, S, and PC. Coaches can now set the loading of the activity to maximize power output.
Hydration performance factors Researchers determined the effect of a 48-h period of either fluid restriction (FR), energy restriction (ER), or fluid and energy restriction (FR+ER) on 30-min treadmill time trial (TT) performance in temperate conditions. Thirteen males participated in four randomized 48-hour trials. Control (CON) participants received their estimated energy requirements (2903 Calories/day) plus water (3912mL/day).
FR received their energy requirements plus 193mL/day water to drink; ER received their water requirements and 290 Calories/day. F+ER was a combination of FR and ER. After 48 hour, participants performed a 30-minute treadmill TT and results revealed that body mass loss averaged 0.6% with CON and ranged from 3.2-3.6% for FR, ER and FR + ER. Compared with CON (average 6295m), less distance was completed by ER (10.3%) and F + ER (15.0%) and FR (2.8%), though the latter is not statistically different from CON.
These results show a detrimental effect of a 48-hour period of energy restriction but no significant effect of fluid restriction on 30-minute treadmill TT performance in temperate conditions. These results do not support the popular belief that modest hypo-hydration (2-3% BML) significantly impairs endurance performance in temperate conditions.
A further paper acknowledges that dehydration may impair endurance performance, but asks the question 'can a reduced body mass though reduced hydration benefit uphill cycling by increasing the power-to-mass ratio?' The study examined the effects of a reduction in body mass attributable to sweat losses on simulated cycling hill-climbing performance in the heat. Eight well-trained male cyclists completed a maximal graded cycling test on a stationary ergometer to determine maximal aerobic power (MAP). Cyclists then performed a 2-hour ride at 53% MAP on a stationary ergometer, immediately followed by a cycling hill-climb time-to-exhaustion trial (88% MAP) on their own bicycle on an inclined treadmill (8%) at approximately 30 degrees C. During the 2-hour ride, they consumed either 2.4 L of a 7% carbohydrate (CHO) drink (HIGH) or 0.4 L of water (LOW) with sport gels to match for CHO content.
After the 2-hour ride and before the hill climb, drinking strategies influenced body mass (LOW average -2.5% vs. HIGH average +0.3%). Despite being approximately 1.9 kg lighter, time to exhaustion was significantly reduced by 28.6%. Exercise-induced dehydration in a warm environment is detrimental to laboratory cycling hill-climbing performance despite reducing the power output required for a given speed.
In sports involving pivoting and landing, female athletes suffer knee injury at a greater rate than male athletes. A study based on 277 collegiate athletes (140 female, 137 male) tested for core proprioception by active and passive proprioceptive repositioning examined the hypothesis that proprioceptive deficits in control of the body's core may affect dynamic stability of the knee and that female, but not male, athletes who suffered a knee injury during a 3-year follow-up period would demonstrate decreased core proprioception at baseline testing as compared with uninjured athletes. 25 of the athletes had sustained knee injuries (11 women, 14 men). Deficits in active proprioceptive repositioning were observed in women with knee injuries (2.2°) and ligament/meniscal injuries (2.4°) compared with uninjured women (1.5°). There were no differences in average active proprioceptive repositioning error between injured men and uninjured men. Uninjured women demonstrated significantly less average error in active proprioceptive repositioning than uninjured men (1.5° vs 1.7°). For each degree increase in average active proprioceptive repositioning error, a 2.9-fold increase in the odds ratio of knee injury was observed, and a 3.3-fold increase in odds ratio of ligament/meniscal injury was observed. Active proprioceptive repositioning predicted knee injury status with 90% sensitivity and 56% specificity in female athletes. The key finding from this study was that impaired core proprioception, measured by active proprioceptive repositioning of the trunk, predicted knee injury risk in female, but not male, athletes. Development of core proprioception may help to reduce nee injury risks in females.
The mechanisms of anterior cruciate ligament injury in basketball are not well defined. A study set out to describe the mechanisms of such injury in basketball based on videos of injury situations. Six international experts performed visual inspection analyses of 39 videos (17 male and 22 female players) of anterior cruciate ligament injury situations from high school, college, and professional basketball games. Two predefined time points were analyzed: initial ground contact and 50 milliseconds later. The analysts were asked to assess the playing situation, player behaviour, and joint kinematics.
There was contact at the assumed time of injury in 11 of the 39 cases (5 male and 6 female players). Four of these cases were direct blows to the knee, all in men. Eleven of the 22 female cases were collisions, or an opponent pushed the player before the time of injury. The estimated time of injury (group median) ranged from 17 to 50 milliseconds after initial ground contact. The mean knee flexion angle was higher in female than in male players, both at initial contact (15° vs. 9°) and at 50 milliseconds later (27° vs. 19°). Valgus knee collapse occurred more frequently in female players than in male players.
Researchers found that female players landed with significantly more knee and hip flexion and had a 5.3 times higher relative risk of sustaining a valgus collapse than did male players. Opponents most frequently perturbed movement patterns. Preventive programs to enhance knee control should focus on avoiding valgus motion and include distractions resembling those seen in match situations. Although ankle sprains are common in soccer, the role of various risk factors in amateur soccer players is unclear. To identify the incidence of ankle sprain injuries associated time loss of participation, and risk factors during two consecutive seasons in amateur players was studied. Of 336 athletes enrolled in the study, 312 male amateur soccer players were observed during a 2-year period. Ankle sprain injury incidents, participation time loss, injury mechanisms, ankle region injured, and other risk factors were recorded in games and practice sessions using questionnaires.
During the study 208 ankle injuries were recorded, of which 139 were ankle sprains. These led to 975 sessions lost (on average, 7 lost sessions per injury). Most incidents (80.6%) were contact injuries, occurring mostly in defenders. Injury rates were equal between games and practice, while 61.1% of injuries were observed toward the end of each half of the game. The injury incidence rate was higher during the first 2 months of the season as opposed to the last month. Statistical analysis showed that previous ankle sprain is a significant predictor of ankle sprain injury.
Ankle sprain injuries in amateur soccer players are primarily contact injuries, occurring mainly in defenders and during both games and practice. It appears that more injuries occur in players with previous ankle injury. Injury rates are higher toward the end of a game and chiefly occur during the first 2 months of the season.
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About the Author
Nigel Hetherington is the Head Track & Field Coach at the internationally acclaimed Singapore Sports School. He is a former National Performance Development Manager for Scottish Athletics and National Sprints Coach for Wales. Qualified and highly active as a UK Athletics (UKA) level 4 performance coach in all events he has coached athletes to National and International honours in sprints, hurdles as well as a World Record holder in the Paralympic shot. He has 10 years experience as senior coach educator and assessor trainer on behalf of UKA. Nigel is also an experienced athlete in sprint (World Masters Championship level) and endurance (3-hour marathon runner plus completed the 24 hour 'Bob Graham Round' ultra-endurance event up and down 42 mountain peaks in the English Lake District). He is a chartered chemist with 26 years' experience in scientific research and publishing.
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