Neck muscle activity in skydivers during parachute opening shock.

This observational study investigated skydiver neck muscle activity during parachute opening shock (POS), as epidemiological data recently suggested neck pain in skydivers to be related to POS. Twenty experienced skydivers performed two terminal velocity skydives each. Surface electromyography quantified muscle activity bilaterally from the anterior neck, the upper and lower posterior neck, and the upper shoulders; and two triaxial accelerometers sampled deceleration. Muscle activity was normalized as the percentage of reference maximum voluntary electrical activity (% MVE); and temporal muscle activity onset was related to POS onset. Our results showed that neck muscle activity during POS reached mean magnitudes of 53-104% MVE, often exceeding reference activity in the lower posterior neck and upper shoulders. All investigated muscle areas' mean temporal onsets occurred <50 ms after POS onset (9-34 ms latencies), which is consistent with anticipatory motor control. The high muscle activity observed supports that the neck is under substantial strain during POS, while temporal muscle activation suggests anticipatory motor control to be a strategy used by skydivers to protect the cervical spine from POS. This study's findings contribute to understanding the high rates of POS-related neck pain, and further support the need for evaluation of neck pain preventative strategies.

Effects of eccentric training on hand strength in subjects with lateral epicondylalgia: a randomized-controlled trial.

The main aim of this study was to evaluate the short-term effects of daily eccentric exercises on functional pain-free hand strength in subjects with long-term lateral epicondylalgia. Forty-two subjects with lateral epicondylalgia were randomly assigned either to a 6-week home exercise regimen receiving eccentric training for their wrist extensors and a forearm band or to a control group receiving a forearm band only. The main outcomes were pain-free hand-grip and wrist-extensor strength at mid- and end-intervention follow-ups, 3 and 6 weeks after inclusion, respectively. Secondary outcomes were a change in the proportion of cases with epicondylalgia and ratings of perceived pain (VAS) at follow-up. Thirty-seven (88%) subjects completed both the mid- and the end-intervention follow-up. Exercise members had significantly higher pain-free hand-grip (P=0.025) and wrist-extensor strength (P<0.001) at the end of follow-up, although there was no such effect at mid-intervention. Regression analysis showed a reduction in the proportion of cases in the exercise group at the end of follow-up (P=0.035). However, no between-groups effect emerged for perceived pain. These data suggest that the daily home eccentric exercise regimen is effective in increasing functional pain-free grip strength and reducing cases suffering from lateral epicondylalgia. However, no effect emerged for global perceived pain during the last week.

Ankle-joint mobility and standing squat posture in elite junior cross-country skiers. A pilot study.

AIM: Skating technique in cross-country skiing is a complex multi-joint movement with kinematics comparable to those of the standing squat exercise where any restricted joint mobility in the lower extremity-chain may change the movement pattern. The aim of this pilot study was to investigate the effect of ankle mobility on trunk posture during squat exercise in cross-country skiers. METHODS: Seven elite junior cross-country skiers (age range 17-19 years) performed two different standing squats, one with hands on hips and one with arms extended above the head. The squats were recorded on video and analyzed in selected positions: 90 degrees and maximal knee flexion. Segment angles for shank and trunk were calculated from anatomical references relative to vertical/horizontal orientation in space. Recordings from passive ankle dorsiflexion were correlated with 1) trunk flexion, and 2) angle index (trunk flexion relative to shank angle). RESULTS: Reduced ankle dorsiflexion was moderately associated with increased trunk flexion with hands on hips (r=-0.51 to -0.57), and arms above head (r=-0.61 to -0.64). Further, reduced dorsiflexion was also moderately associated with decreased angle index with hands on hip (r=0.60 to 0.67) but highly associated with decreased angle index with arms above head (r=0.75 to 0.76). CONCLUSION: The results imply that reduced ankle dorsal mobility is related to decreased angle index as well as increased trunk flexion during squat exercise, thus indicating the relevance of good ankle joint mobility for appropriate upper-body posture during squat exercise.

Predictive factors for 12-month outcome after anterior cruciate ligament reconstruction.

There is a lack of knowledge regarding predictive factors for a successful clinical outcome after an anterior cruciate ligament (ACL) reconstruction. The aim was to investigate pre-operative factors that may predict good outcomes as measured with the subscales Function in sports and recreation and Quality of life in Knee injury Osteoarthrithis Outcome Score (QOL-KOOS), one-leg hop test and Tegner Activity Scale 12 months after ACL reconstruction. Sixty-four patients, operated with either patellar or hamstring tendon graft, were included. Demographics, range of motion, anterior knee laxity, pivot shift, muscle-torques, anterior knee pain (AKP) and knee function were registered pre-operatively and used in a multiple regression model. Results show less degree of AKP and low influence on knee function to be the most important predictors for good outcome in Sport/Rec-KOOS (explained 31% of variances). Less AKP was in addition the most important predictor for QOL-KOOS (14%). Patellar-tendon graft, in favor of hamstring tendon graft, explained 8% of the improvement in the Tegner Activity Scale. In conclusion, a low degree of AKP was found to be the most important predictor for good clinical outcome 12 months after ACL reconstruction. Future studies, including psychological parameters, should use analyses that have the potential to control for independency between variables.