Head-torso coordination in police officers wearing loaded tactical vests during running

BACKGROUND

The influence of load carriage in operational police officers is not well understood despite a relatively high injury rate. Assessing load related changes in head and torso coordination may provide valuable insight into plausible injury mechanisms.

RESEARCH QUESTION

Do typical police tactical vest loads alter head and torso coordination during running?

METHODS

Thirty-eight UK police officers ran at a self-selected pace (>2 ms-1) on a non-motorised treadmill in four vest load conditions (unloaded, and low, high and evenly distributed loads). Peak head and torso tilt, and peak vest displacement were compared between all four conditions. Timings between vest and torso change of direction were compared between the three loaded conditions. The coupling angle between the head and torso calculated using modified vector coding were compared between unloaded and each loaded conditions using Statistical Parametric Mapping.

RESULTS

No significant differences were found between conditions for peak head or torso tilt alone (p > 0.05). Loading equipment low on the vest led to significantly greater mediolateral vest displacements (38 mm) away from the torso than a high (34 mm) or evenly distributed (30 mm) conditions. The vest was found to change direction vertically before the torso in the anterior-posterior direction, and then influence torso motion. The loaded conditions changed the head-torso coupling from in-phase (with head-dominancy) to anti-phase (with torso dominancy) between 55% and 77% stance. Anti-phase with a relatively stationary head and the torso rotating forward likely places a greater concentric demand on the posterior neck muscles relative to unloaded running.

SIGNIFICANCE

Current tactical vest designs allow significant extra displacement of load away from the body during running, altering coordination at the head and torso.

Do non-rearfoot runners experience greater second metatarsal stresses than rearfoot runners?

Stress fracture of the second metatarsal is a common and problematic injury for runners. The choice of foot strike pattern is known to affect external kinetics and kinematics but its effect on internal loading of the metatarsals is not well understood. Models of various complexities can be used to investigate the effects of running characteristics on metatarsal stresses. This study aimed to compare second metatarsal stress between habitual rearfoot and non-rearfoot strikers during barefoot running, using a novel participant-specific finite element model, including accurate metatarsal and soft tissue geometry. Synchronised force and kinematic data were collected during barefoot overground running from 20 participants (12 rearfoot strikers). Stresses were calculated using a previously evaluated and published 3D finite element model. Non-rearfoot strikers demonstrated greater external loading and joint contact forces than rearfoot runners, but there were no differences in stresses between groups. Additionally, the study allowed for a qualitative assessment of bone geometries and stresses. No correlation was found between bone volume and stresses, however, there was found to be a large variation in metatarsal shapes, possibly accounting for the lack of difference in stresses. This emphasises the importance of bone geometry when estimating bone stress and supports the suggestion that external forces should not be assumed to be representative of internal loading.

Delayed healing of rhytidectomy flap resurfaced with CO2 laser

Combining facial rhytidectomy with laser resurfacing, theoretically, provides the best opportunity for achieving an optimal facial rejuvenation result. Previous studies have demonstrated the pernicious effect of a deep peel on a skin flap, but the safety of treating the rhytidectomy flap with laser has not been investigated. This study was conducted to investigate the safety of using these techniques concomitantly. Sixty sites were selected on three Yucatan minipigs, a species of swine chosen because of its hairless nature and opportunity to raise a true skin flap (without the panniculus carnosus). The healing time of 20 laser-treated sites without flap elevation was compared with that of 20 areas treated with laser following flap elevation, shortening (to emulate a more realistic rhytidectomy process), and repair. Twenty flaps were elevated and shortened without laser treatment to serve as a control. The CO2 laser parameters were set at 500 mJ, 50 watts, and a density of 5. Two passes were made to penetrate the upper dermis. The mean healing time for areas treated with laser alone was 12.05 days, ranging from 11 to 14 days. In comparison, the healing time for the laser-treated areas subsequent to flap elevation averaged 17.95 days, with a range of 14 to 24 days (p < 0.05). Two flaps treated with laser (10 percent) failed to heal completely in 24 days. At the time that all 20 of the areas treated solely with laser had re-epithelialized completely, only one of the flaps treated with laser had re-epithelialized completely (p < 0.001). A delay in healing, as well as return of pigment, was demonstrated in the distal portions of all flaps receiving laser treatment. The control flaps all healed normally except for a 5-percent superficial loss on a single flap. It was concluded from this study, and from clinical observation of delayed healing on six of seven patients who underwent concomitant rhytidectomy and laser resurfacing at a conservative laser setting, that laser resurfacing of the rhytidectomy flap is unsafe and results in delayed re-epithelialization. This combination should be avoided altogether or performed with extreme prudence on patients undergoing a deeper plane facial rhytidectomy or by using very low laser settings.