Isokinetic Leg Flexion and Extension Strength of Elite Adolescent Female Track and Field Athletes

Abstract

Sixty-two elite adolescent (age: 16.39 ± 1.62 yrs) female track and field athletes volunteered to be measured isokinetically for peak torque of the leg flexors and extensors. The sample included 16 throwers, 11 jumpers, 12 middle-distance runners (> 400 m), and 23 sprinters. A Cybex II isokinetic dynamometer was used to measure dominant leg strength at 180°/sec. One-way ANOVA revealed significant between group differences for absolute flexion and extension (Nm), extension/body weight (Nm/Kg), and extension/lean body weight (Nm/Kg). Scheffe post-hoc comparisons showed that, for absolute leg extension strength, throwers were stronger than middle-distance runners (by 54.4%), sprinters (35.6%), and jumpers (23.6%). For absolute leg flexion movements, throwers were stronger than middle distance runners (37.4%) and sprinters (32.1%). Jumpers had greater extension peak torque values than middle-distance runners relative to body weight (14.0%), and throwers were stronger than middle-distance runners for extension/lean body weight (14.9%)). No other comparisons were significant. However, when strength was expressed relative to body weight or lean body weight, there were few differences between events for flexion or extension. Given that absolute strength scores were correlated with body weight and lean body weight, peak torque/body weight or peak torque/lean body weight may be more sensitive than absolute values as indicators of underlying factors (such as training status or fiber type composition) responsible for the differences in muscular strength between groups.     

Acute kinematic and kinetic adaptations to wearable resistance during vertical jumping

One variation of vertical jump (VJ) training is resisted or weighted jump training, where wearable resistance (WR) enables jumping to be overloaded in a movement specific manner. A two-way analysis of variance with Bonferroni post hoc contrasts was used to determine the acute changes in VJ performance with differing load magnitudes and load placements. Kinematic and kinetic data were quantified using a force plate and contact mat. Twenty sport active subjects (age: 27.8?±?3.8 years; body mass (BM): 70.2?±?12.2?kg; height: 1.74?±?0.78?m) volunteered to participate in the study. Subjects performed the counter movement jump (CMJ), drop jump (DJ) and pogo jump (PJ) wearing no resistance, 3% or 6% BM affixed to the upper or lower body. The main finding in terms of the landing phase was that the effect of WR was non-significant (P?>?.05) on peak ground reaction force. With regard to the propulsive phase the main findings were that for both the CMJ and DJ, WR resulted in a significant (P?<?.05) decrease in jump height (CMJ: ?12% to ?17%, DJ: ?10% to ?14%); relative peak power (CMJ: ?8% to ?17%, DJ: ?7% to ?10%); and peak velocity (CMJ: ?4% to ?7%, DJ: ?3% to ?8%); while PJ reactive strength index was significantly reduced (?15% to ?21%) with all WR conditions. Consideration should be given to the inclusion of WR in sports where VJ’s are important components as it may provide a novel movement specific training stimulus.

Highlights

• WR of 3 or 6 % BM provided a means to overload the subjects in this study resulting in decreased propulsive power and velocity that lead to a reduced jump height and landing force.

• Specific strength exercises that closely mimic sporting performance are more likely to optimise transference, therefore WR with light loads of 3–6% body mass (BM)appear a suitable tool for movement specific overload training and maximising transference to sporting performance.

• Practitioners can safely load their athletes with upper or lower body WR of 3–6% BM without fear of overloading the athletesover and above the landing forces they are typically accustomed too.

• As a training stimulus it would seem the WR loading provides adequate overload and athletes should focus on velocity of movement to improve power output and jump height i.e. take-off velocity.

     

Accelerated hydrothermal degradation of fibres of Phormium tenax (New Zealand flax)

Solid-phase microextraction (SPME)–gas chromatography (GC)–mass spectrometry (MS) has been applied to the analysis of acetic acid and furfural that are emitted from the fibres of Phormium tenax (Xanthorrhoeaceae) [New Zealand flax] during degradation. Accelerated hydrothermal ageing of fibres of the Ruawai cultivar of P. tenax for 55 days at 70 °C resulted in the production of acetic acid at a level greater or equal to 1.65 mg g^–1 fibre. This corresponds to only 8.5% of the acetyl groups present in the fibres. These groups are an important source of acetic acid, which is capable of damaging the fibres. The rate of production of acetic acid suggests that a heritage object made from the fibres of P. tenax, that was stored in damp ambient conditions, would undergo significant deterioration after a relatively short period. Other volatile products released during ageing included furfural, a series of short to medium chain aliphatic aldehydes that were derived from the oxidation of long chain unsaturated fatty acids on the fibres and a small group of products that were derived from carotenoids. The levels of furfural were determined to be approximately 0.75% of the potential production but at these levels, furfural could contribute to unpleasant odours from unventilated items. Fibres from six cultivars of P. tenax were found to release acetic acid and furfural all at the same rate. The levels of acetic acid that can be generated from these fibres are sufficiently high that low moisture levels and continuous change of air is required to minimize degradation of cultural objects that are made from these fibres and displayed in museum halls.     

Untangling the Links among Athletic Involvement, Gender, Race, and Adolescent Academic Outcomes

Although previous research has established that high school sports participation may be associated with positive academic outcomes, the parameters of the relationship remain unclear. Using a longitudinal sample of nearly 600 Western New York adolescents, this study examined gender- and race-specific differences in the impact of two dimensions of adolescent athletic involvement ("jock" identity and athlete status) on changes in school grades and school misconduct over a two-year interval. Female and black adolescents who identified themselves as "jocks" reported lower grades than those who did not, whereas female athletes reported higher grades than female nonathletes. Jocks also reported significantly more misconduct (including skipping school, cutting classes, having someone from home called to the school for disciplinary purposes, and being sent to the principal's office) than nonjocks. Gender moderated the relationship between athlete status and school misconduct; athletic participation had a less salutary effect on misconduct for girls than for boys.