Acute effects of prior conditioning activity on change of direction performance. A systematic review and meta-analysis.

We performed a systematic review and meta-analysis on the acute effects of prior conditioning activity (CA) on change of direction (COD) performance. Eligible studies, involving healthy participants undergoing acute CA with at least one measure of COD performance, were analysed across diverse databases. A total of 34 studies were included for systematic review with 19 studies included for the meta-analysis. The intervention condition resulted in significantly faster (Z = 4.39; standard mean difference [SMD] = 0.49; p < 0.05) COD performance compared with the control condition. Both unloaded and light loaded CA resulted in significantly greater (SMD = 0.58-0.59) COD performance compared to the control condition. Moreover, heavy loaded CA demonstrated a significant but small (SMD = 0.24) improvement in COD performance compared to the control condition. Age and study design had no effect on the overall meta-analysis outcomes. Both males and females exhibited similar moderate effects with CA but only males demonstrated significantly greater COD performance compared to control conditions. Our findings indicate that a range of CA protocols can acutely improve COD performance with unloaded and light-loaded CA resulting in the greatest performance enhancements. These findings will assist practitioners with the design and implementation of appropriate acute CA to improve COD performance.

The validity of using inertial measurement units to monitor the torso and pelvis sagittal plane motion of elite rowers.

In elite sport, inertial measurement units (IMUs) are being used increasingly to measure movement in-field. IMU data commonly sought are body segment angles as this gives insights into how technique can be altered to improve performance and reduce injury risk. The purpose of this was to assess the validity of IMU use in rowing and identify if IMUs are capable of detecting differences in sagittal torso and pelvis angles that result from changes in stroke rates. Eight elite female rowers participated. Four IMUs were positioned along the torso and over the pelvis of each athlete. Reflective markers surrounded each IMU which were used to compute gold-standard data. Maxima, minima, angle range and waveforms for ten strokes at rates of 20, 24, 28 and 32 strokes per minute were analysed. Root mean square errors as a percentage of angle range fell between 1.44% and 8.43%. In most cases when significant differences (p < 0.05) in the angles were detected between stroke rates, this was observed in both IMU and gold-standard angle data. These findings suggest that IMUs are valid for measuring torso and pelvis angles when rowing and are capable of detecting differences that result from changes in stroke rate.

Effect of Footwear on the Biomechanics of Loaded Back Squats to Volitional Exhaustion in Skilled Lifters.

ABSTRACT: Brice, SM, Doma, K, and Spratford, W. Effect of footwear on the biomechanics of loaded back squats to volitional exhaustion in skilled lifters. J Strength Cond Res 36(10): 2676-2684, 2022-This study examined whether footwear influences the movement dynamics of barbell back squats to volitional exhaustion in experienced lifters. Eleven men (1 repetition maximum [1RM] = 138 ± 19 kg; 1RM % body mass = 168 ± 18%) performed 3 sets (5-12 ± 4 repetitions per set) of loaded barbell back squats to volitional exhaustion using raised-heel and flat-heel footwear. Barbell motion as well as moments, angles, angular velocity, and power in the sagittal plane at the ankle, knee, hip, and lumbopelvis were examined during the second repetition of the first set (T second ) and the final repetition of the third set (T final ). There were significant reductions ( p < 0.05) in lower-limb concentric angular velocity and power output for both footwear conditions. For the raised-heel condition at T final , hip and knee concentric angular velocities were significantly slower ( p < 0.05), and knee concentric power output was significantly less ( p < 0.05) compared with the flat-heel condition. A reduction in barbell velocity was not observed for the raised-heel condition despite there being reduction in hip and knee angular velocities. Furthermore, no differences were identified in lower-limb joint moments or any of the biomechanical characteristics of the lumbopelvis between the footwear conditions. The findings of this study suggest that neither type of footwear reduced joint loading or improved joint range-of-motion.

Overuse injuries in runners of different abilities-a one-year prospective study.

The aim of this prospective study was to investigate differences in participant characteristics, previous injury, running dynamics during a long-distance run, and training between injured and uninjured runners in runners of different abilities. Center-of-mass acceleration data were collected during a long-distance overground run. Runners were then divided into four groups (elite, advanced, intermediate and slow) based on their finishing time. Participants completed training diaries and were monitored for 1 year. Seventy-six runners completed the prospective study with 39 (51.3%) sustaining a running injury (44% elite, 42% advanced, 54% intermediate, 59% slow). Differences between injured and uninjured runners within each group related to injury included: (1) elite injured runners ran with longer contact times and (2) more slow injured runners reported an injury in previous year, were heavier, had higher body mass and body mass index, ran with lower step frequencies, and ran a greater weekly distance. Advanced injured runners exhibited fatigue changes in step regularity and peak braking during the run that may be related to injury. These findings suggest that runners of different abilities may have different factors related to injury however due to the small sample sizes in the groups this needs to be explored further.

Impact of performing heavy-loaded barbell back squats to volitional failure on lower limb and lumbo-pelvis mechanics in skilled lifters.

A common practice in resistance training is to perform sets of exercises at, or close to failure, which can alter movement dynamics. This study examined ankle, knee, hip, and lumbo-pelvis dynamics during the barbell back squat under a moderate-heavy load (80% of 1 repetition maximum (1RM)) when performed to failure. Eleven resistance trained males performed three sets to volitional failure. Sagittal plane movement dynamics at the ankle, knee, hip, and lumbo-pelvis were examined; specifically, joint moments, joint angles, joint angular velocity, and joint power. The second repetition of the first set and the final repetition of the third set were compared. Results showed that while the joint movements slowed (p < 0.05), the joint ranges of motion were not altered There were significant changes in most mean joint moments (p < 0.05), indicating altered joint loading. The knee moment decreased while the hip and lumbo-pelvis moments underwent compensatory increases. At the knee and hip, there were significant decreases (p < 0.05) in concentric power output (p < 0.05). Whilst performing multiple sets to failure altered some joint kinetics, the comparable findings in joint range ofmotion suggest that technique was not altered. Therefore, skilled individuals appear to maintain technique when performing to failure.

An analysis of the relationship between the linear hammer speed and the thrower applied forces during the hammer throw for male and female throwers.

The purpose of this study was to investigate the relationship between the cable force and linear hammer speed in the hammer throw and to identify how the magnitude and direction of the cable force affects the fluctuations in linear hammer speed. Five male (height: 1.88 +/- 0.06 m; body mass: 106.23 +/- 4.83 kg) and five female (height: 1.69 +/- 0.05 m; body mass: 101.60 +/- 20.92 kg) throwers participated and were required to perform 10 throws each. The hammer's linear velocity and the cable force and its tangential component were calculated via hammer head positional data. As expected, a strong correlation was observed between decreases in the linear hammer speed and decreases in the cable force (normalised for hammer weight). A strong correlation was also found to exist between the angle by which the cable force lags the radius of rotation at its maximum (when tangential force is at its most negative) and the size of the decreases in hammer speed. These findings indicate that the most effective way to minimise the effect of the negative tangential force is to reduce the size of the lag angle.

A Multifactorial Approach to Overuse Running Injuries: A 1-Year Prospective Study.

BACKGROUND: Because of the complex and multifaceted nature of running injuries, a multifactorial approach when investigating running injuries is required. HYPOTHESIS: Compared with uninjured runners, injured runners would exhibit different running biomechanics, display more fatigue changes, and would run a greater weekly running volume; more injured runners would also report having a previous injury. STUDY DESIGN: Prospective cohort study. LEVEL OF EVIDENCE: Level 4. METHODS: At commencement of the study, data were collected on demographics, anthropometrics, training history, previous injury history, and center-of-mass accelerations during a long-distance overground run. Participants completed weekly training diaries and were monitored for 1 year for an injury. RESULTS: A total of 76 runners completed the study, with 39 (22 male; 17 female) reporting an injury. Compared with male uninjured runners, male injured runners were heavier and ran a greater weekly distance. Male runners (injured and uninjured) exhibited increases in mediolateral center-of-mass accelerations during the run. Compared with female uninjured runners, female injured runners were heavier, ran with longer flight times and lower step frequencies, and more of them had reported an injury in the previous year and had increased speed training in the weeks prior to injury. Over 60% of male injured runners and over 50% of female injured runners had increased their weekly running distance by >30% between consecutive weeks at least once in the 4 weeks prior to injury. CONCLUSION: Factors that may be related to injury for male runners include being heavier, running a greater weekly distance, and exhibiting fatigue changes in mediolateral center-of-mass accelerations. Factors that may be related to injury for female runners include being heavier, having an injury in the previous year, running with longer flight times and lower step frequencies, and increasing speed training prior to injury. Increases in weekly running distance in 1 consecutive week (particularly >30%) needs to be monitored in training, and this along with the other factors found may have contributed to injury development. CLINICAL RELEVANCE: This study found that multiple factors are related to running injuries and that some factors are sex specific. The findings can aid in injury prevention and management.

Comparing inertial measurement units and marker-based biomechanical models during dynamic rotation of the torso.

Inertial measurement units (IMUs) enable human movements to be captured in the field and are being used increasingly in high performance sport. One key metric that can be derived from IMUs are relative angles of body segments which are important for monitoring form in many sports. The purpose of this study was to (a) examine the validity of relative angles derived from IMUs placed on the torso and pelvis; and (b) determine optimal positioning for torso mounted sensors such that the IMU relative angles match closely with gold standard torso-pelvis and thorax-pelvis relative angle data derived from an optoelectronic camera system. Seventeen adult participants undertook a variety of motion tasks. Four IMUs were positioned on the torso and one was positioned on the pelvis between the posterior superior iliac spines. Reflective markers were positioned around each IMU and over torso and pelvis landmarks. Results showed that the IMUs are valid with the root mean square errors expressed as a percentage of the angle range (RMSE%) ranging between 1% and 7%. Comparison between the IMU relative angles and the torso-pelvis and thorax-pelvis relative angles showed there were moderate to large differences with RMSE% values ranging between 4% and 57%. IMUs are highly accurate at measuring orientation data; however, further work is needed to optimise positioning and modelling approaches so IMU relative angles align more closely with relative angles derived using traditional motion capture methods.

Development and validation of a method to directly measure the cable force during the hammer throw.

The development of cable force during hammer-throw turns is crucial to the throw distance. In this paper, we present a method that is capable of measuring cable force in real time and, as it does not interfere with technique, it is capable of providing immediate feedback to coaches and athletes during training. A strain gauge was mounted on the wires of three hammers to measure the tension in the wire and an elite male hammer thrower executed three throws with each hammer. The output from the gauges was recorded by a data logger positioned on the lower back of the thrower. The throws were captured by three high-speed video cameras and the three-dimensional position of the hammer's head was determined by digitizing the images manually. The five best throws were analysed. The force acting on the hammer's head was calculated from Newton's second law of motion and this was compared with the force measured via the strain gauge. Qualitatively the time dependence of the two forces was essentially the same, although the measured force showed more detail in the troughs of the force-time curves. Quantitatively the average difference between the measured and calculated forces over the five throws was 76 N, which corresponds to a difference of 3.8% for a cable force of 2000 N.