Trunk-pelvis coordination during load carriage running

Determination of dynamic air gap thickness and analysis of its relationship with firefighters' joint movement

Objectives. The purpose of this study was to calculate the dynamic air gap thickness between the human body and the turnout gear. Relationships between the air gap thickness and joint range of motion (ROM) were also explored. Methods. The air gap thickness and joint ROM of 12 male firefighters walking in a control condition with no self-contained breathing apparatus (SCBA) and three varying-strapped SCBAs were measured using three-dimensional (3D) body scanning and 3D inertial motion capture. The interpolation technique was employed to predict the air gap thickness curve during walking. The dynamic air gap thickness was compared with the joint ROM to see how they relate to the location and percentage of movement restriction. Results. During the walking, the air gap fluctuated as a sine curve. Carrying SCBA reduced the air gap thickness at the trunk most (F = 11.17, p < 0.001, η2 = 0.63), and adjusting the shoulder strap length altered the air gap distribution at the trunk. The reduced air gap at the pelvis caused an incremental restriction on pelvis rotation. Conclusions. A compatibility design of the shoulder strap and hip belt in SCBA with the turnout jacket is suggested.

The test-retest reliability of physiological and perceptual responses during treadmill load carriage

PURPOSE

Understanding the test-retest reliability of physiological responses to load carriage influences the interpretation of those results. The aim of this study was to determine the test-retest reliability of physiological measures during loaded treadmill walking at 5.5 km h-1 using the MetaMax 3B.

METHODS

Fifteen Australian Army soldiers (9 male, 6 female) repeated two 12-min bouts of treadmill walking at 5.5 km h-1 in both a 7.2 kg Control condition (MetaMax 3B, replica rifle) and a 23.2 kg Patrol condition (Control condition plus vest) across three sessions, separated by one week. Expired respiratory gases and heart rate were continuously collected, with the final 3 min of data analysed. Ratings of Perceived Exertion and Omnibus-Resistance Exercise Scale were taken following each trial. Reliability was quantified by coefficient of variation (CV), intra-class correlation coefficients (ICC), smallest worthwhile change (SWC), and standard error of the measurement.

RESULTS

Metabolic and cardiovascular variables were highly reliable (≤ 5% CV; excellent-moderate ICC), while the respiratory variables demonstrated moderate reliability (< 8% CV; good-moderate ICC) across both conditions. Perceptual ratings had poorer reliability during the Control condition (12-45% CV; poor ICC) than the Patrol condition (7-16% CV; good ICC).

CONCLUSIONS

The test-retest reliability of metabolic and cardiovascular variables was high and relatively consistent during load carriage. Respiratory responses demonstrated moderate test-retest reliability; however, as the SWC differed with load carriage tasks, such data should be interpreted independently across loads. Perceptual measures demonstrated poor to moderate reliability during load carriage, and it is recommended that they only be employed as secondary measures.

Kinematical effects of rifle carriage on roller skiing in well-trained female and male biathletes

PURPOSE

This study aimed to investigate how rifle carriage and skiing speed during biathlon roller skiing affect range of motion (ROM) in joint angles and equipment (skis and poles), the vertical distance between shoulders and treadmill (vert_dist ), as well as possible sex differences associated with rifle carriage.

METHODS

Fourteen biathletes (6 women, 8 men) roller-skied on a treadmill at submaximal and simulated race speeds, with (WR) and without (NR) a rifle, using gears 3 and 2. Kinematical data for the whole body, poles, roller-skis, rifle, and treadmill were monitored using a 3D motion capture system. Movements determined as flexion/extension (x), abduction/adduction (y), and/or internal/external rotation (z) were analyzed for the hip, shoulder, thorax, knee, ankle, elbow, poles, and roller skis. ROM (the difference between maximal and minimal angles) in joints and equipment, and vert_dist were analyzed over six skiing cycles during each condition (WR and NR) and speed.

RESULTS

The maximal vert_dist was lower for WR compared with NR (gear 3: 1.53 ± 0.06 vs 1.54 ± 0.06 m; gear 2: 1.49 ± 0.06 vs 1.51 ± 0.06 m; both p < 0.001). ROM in the upper body was altered when roller skiing WR (movements decreased in thorax and shoulder (x) and increased in elbow (only gear 3) (x), thorax (only gear 2), and shoulder (y) and (z); all p < 0.05) and increased with speed, without differences between sexes (p > 0.05).

CONCLUSION

Since rifle carriage and speed appear to affect the kinematics of roller skiing, coaches, and biathletes are advised to perform skiing technique training under competition-like conditions (i.e., at race speeds while carrying the rifle).

The effect of external loads and biological sex on coupling variability during load carriage

BACKGROUND

Load carriage is a fundamental requirement for military personnel that commonly results in lower-limb injuries. Coupling variability represents a potential injury mechanism for such repetitive tasks and its unknown whether external loads and biological sex affect coupling variability during load carriage.

RESEARCH QUESTION

Is there a sex-by-load interaction during load carriage at self-selected walking speeds?

METHODS

Twenty-six participants (13 males, 13 females) completed three 10-minute treadmill-based trials wearing body-borne external load (0 %BM, 20 %BM, and 40 %BM) at load-specific self-selected walking speeds. A Vicon motion capture system tracked markers with a lower-body direct-kinematic model calculating sagittal-plane segment kinematics of the thigh, shank, and foot across 19 strides. Continuous relative phase standard deviation (CRPv) provided a measure of coupling variability for each coupling angle (Thigh-Shank and Shank-Foot). The CRPv for each load and sex was compared using statistical parametric mapping repeated measures ANOVA and paired t tests.

RESULTS

Significant sex-by-load interactions were reported for the Thigh-Shank coupling. Males demonstrated no significant load differences in CRPv, however, females displayed significantly higher CRPv in the 40 %BM than the 0 %BM condition. A significant main effect of load was observed in the Shank-Foot coupling, with the 40 %BM having significantly greater CRPv than the other load conditions.

SIGNIFICANCE

Both biological sex and external loads significantly affected CRPv during load carriage at self-selected walking speeds. Females demonstrated greater CRPv at the heavier loads, suggesting that the perturbation from the heavier mass increases coupling variability, which may also be amplified by a greater total passive load due to their relatively higher adipose tissue compared to males. The consistent CRPv in males suggests that higher relative loads may be required to change coupling variability. Collectively, these results suggest that external load affects the coupling variability of males and females differently, providing potential for injury screening and monitoring programs.

Effects of Occupational Load on the Acceleration, Change of Direction Speed, and Anaerobic Power of Police Officers

ABSTRACT

Kukić, F, Janković, R, Dawes, JJ, Orr, R, and Koropanovski, N. Effects of occupational load on the acceleration, change of direction speed, and anaerobic power of police officers. J Strength Cond Res XX(X): 000-000, 2022-Police officers engage in movements such as foot pursuits, sudden directional changes, or prolonged sprinting while wearing occupational loads (including body armor, baton, radio, handcuffs, and sidearm). This study investigated the effects of incrementally heavier loads carried by police students on their physical performance. Police students (n = 63; male n = 39 male and 24 female students) performed an acceleration over a 10-m distance (Acc10m), Illinois agility test (IAT), and 300-yard shuttle run test (ShR300y) without load, with a 5-kg load (handgun, spare empty magazine, baton, and handcuffs), and with a 10-kg load (loaded vest). The effects of different load conditions were investigated for both sexes using a repeated-measure analysis of variance and Cohen's effect size. Female students carried relatively heavier loads and were slower than male students in Acc10m, IAT, and ShR300y. Load significantly (p < 0.001) impaired the performance in Acc10m, IAT, and ShR300y in both sexes, but the effects were greater (p < 0.001) among female police students. A load as little as 5 kg was sufficient to reduce Acc10m, IAT, and ShR300y among police students. Increasing the load to 10 kg (i.e., wearing the body armor) did not significantly affect Acc10m and IAT among male students, but it did affect Acc10m and IAT among female students. Sprint endurance (i.e., ShR300y) was strongly affected by both loads regardless of sex. Strength and conditioning programs should focus on strength, power, and anaerobic endurance to improve performance while carrying occupational loads. Occasional training with loads similar to those at work may further ensure that officers are fit for purpose.

Effects of different hydration supports on stride kinematics, comfort, and impact accelerations during running

BACKGROUND

Different supports for hydration can influence total body mass and affect running biomechanics.

RESEARCH QUESTION

Do different hydration supports affect the perceived exertion and comfort, stride kinematics, and impact accelerations during running?

METHODS

This was a crossover study design. Thirteen trail runners completed a treadmill running test divided into four different durations and randomized hydration supports conditions, lasting 8 min each at moderate intensity: A) waist bag (0.84 kg); B) medium load backpack (0.84 kg); C) full load backpack (3.40 kg); and D) a control condition without water support. Impact accelerations were measured for 30 s in 4, 6, and 8 min. The rate of perceived exertion and heart rate were registered on minutes 4 and 8. At the last minute of each condition, comfort perception was registered RESULTS AND SIGNIFICANCE: No condition affected the stride kinematics. Full load backpack condition reduced head acceleration peak (-0.21 g; p = 0.04; ES=0.4) and head acceleration magnitude (-0.23 g; p = 0.03; ES=0.4), and increased shock attenuation (3.08 g; p = 0.04; ES=0.3). It also elicited higher perceived exertion (p < 0.05; ES>0.8) being considered heavier (p < 0.01; ES > 1.1). The waist bag condition was more comfortable in terms of noise (p = 0.006; ES=1.3) and humidity/heat (p = 0.001; ES=0.8). The waist bag was the most comfortable support. On the other hand, the full backpack elicited lower comfort and was the only generating compensatory adjustments. These results may help to improve design of full load backpack aiming at comfort for runners.