Shoulder and Lower Back Joint Reaction Forces in Seated Double Poling.

Overuse injuries in the shoulders and lower back are hypothesized to be common in cross-country sit-skiing. Athletes with reduced trunk muscle control mainly sit with the knees higher than the hips (KH). To reduce spinal flexion, a position with the knees below the hips (KL) was enabled for these athletes using a frontal trunk support. The aim of the study was to compare the shoulder joint (glenohumeral joint) and L4-L5 joint reactions of the KL and KH sitting positions. Five able-bodied female athletes performed submaximal and maximal exercise tests in the sitting positions KL and KH on a ski ergometer. Measured pole forces and 3-dimensional kinematics served as input for inverse-dynamics simulations to compute the muscle forces and joint reactions in the shoulder and L4-L5 joint. This was the first musculoskeletal simulation study of seated double poling. The results showed that the KH position was favorable for higher performance and decreased values of the shoulder joint reactions for female able-bodied athletes with full trunk control. The KL position was favorable for lower L4-L5 joint reactions and might therefore reduce the risk of lower back injuries. These results indicate that it is hard to optimize both performance and safety in the same sit-ski.

Estimation of muscular metabolic power in two different cross-country sit-skiing sledges using inverse-dynamics simulation.

The aim of this study was to estimate and compare the muscular metabolic power produced in the human body using musculoskeletal inverse-dynamics during cross-country sit-skiing. Two sitting positions were adapted for athletes with reduced trunk and hip muscle control, knee low with frontal trunk support (KL-fix), and knee high (KH). Five female national class able-bodied cross-country skiers performed submaximal and maximal exercise in both sitting positions, while recording 3-D kinematics, pole forces, electromyography and respiratory variables. Simulations were performed from these experimental results and muscular metabolic power was computed. The main part of the muscle metabolic power was produced in the upper limbs for both sitting positions, but KH produced more muscle metabolic power in lower limbs and trunk during maximal intensity. KH was also more efficient, utilizing less muscular metabolic power during submaximal intensities, relatively less power in the upper limbs and more power in the trunk, hip and lower limb muscles. This implies that sitting position KH is preferable for high power output when using able-bodied simulation models. This study showed the potential of using musculoskeletal simulations to improve the understanding of how different equipment design and muscles contribute to performance.

Development of a novel eccentric arm cycle ergometer for training the upper body.

UNLABELLED: Several investigators have demonstrated that chronic eccentric leg cycling is an effective method for improving lower body neuromuscular function (e.g., quadriceps muscle size, strength, and mobility) in a variety of patient and athletic populations. To date, there are no reports of using eccentric arm cycling (EC(arm)) as an exercise modality, probably in large part because of the lack of commercially available EC(arm) ergometers. PURPOSE: Our purposes for conducting this study were to 1) describe the design and construction of an EC(arm) ergometer and 2) compare EC(arm) to traditional concentric arm cycling (CC(arm)). METHODS: All of the parts of a Monark 891E cycle ergometer (Monark Exercise AB, Vansbro, Sweden) were removed, leaving the frame and flywheel. An electric motor (2.2 kW) was connected to the flywheel via a pulley and a belt. Motor speed and pedaling rate were controlled by a variable frequency drive. A power meter quantified power and pedaling rate, and provided feedback to the individual. Eight individuals performed 3-min EC(arm) and CC(arm) trials at 40, 80, and 120 W (60 rpm) while VO(2) was measured. RESULTS: The EC(arm) ergometer was simple to use, was adjustable, provided feedback on power output to the user, and allowed for a range of eccentric powers. VO(2) during EC(arm) was substantially lower compared with CC(arm) (P < 0.001). At similar VO(2) (0.97 ± 0.18 vs 0.91 ± 0.09 L·min(-1), for EC(arm) and CC(arm), respectively, P = 0.26), power absorbed during EC(arm) was approximately threefold greater than that produced during CC(arm) (118 ± 1 vs 40 ± 1 W, P < 0.001). CONCLUSION: This novel EC(arm) ergometer can be used to perform repetitive, high-force, multijoint, eccentric actions with the upper body at a low level of metabolic demand and may allow researchers and clinicians to use EC(arm) as a training and rehabilitation modality.