Decelerations and muscle responses during parachute opening shock

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1 Decelerations and muscle responses during parachute opening shock MD, PhD 1, 2, 3, Kristofer Gladh PT, Bsc 1, Riccardo Lo Martire PT, Bsc 1, Jenny Nilsson PT, Msc 1, Peter Lindholm MD, PhD 2, Björn Äng PT, PhD 1 1. Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy, Karolinska Institutet, Stockholm, Sweden. 2. Department of Physiology and Pharmacology, Section of Anaesthesiology and Intensive Care, Karolinska Institutet, Stockholm, Sweden. 3. Department of Anaesthesiology and Intensive Care, Karolinska University Hospital Huddinge, Stockholm, Sweden.

2 F = ma Newton's second law: The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object.

3 John Paul Stapp

5 Neck pain in skydivers Questionnaire to Swedish skydivers: 658 responses (70% response rate). Self-reported one year prevalence of neck pain: 45%. General population (Fejer et al., 2006) estimate: 37%. Self-reported one year prevalence of skydiver neck pain related to parachute opening shock (POS): 25%. Fejer R, Kyvik KO, Hartvigsen J. The prevalence of neck pain in the world population: a systematic critical review of the literature. Eur Spine J 2006; 15: Nilsson J, Fridén C, Burén V, Westman A, Lindholm P, Äng B. Musculoskeletal pain and related risks in skydivers: a population-based survey. Aviat Space Environ Med 2013; 84:

literature. Eur Spine J 2006; 15: 834-48.

6 Neck pain in skydivers Fejer R, Kyvik KO, Hartvigsen J. The prevalence of neck pain in the world population: a systematic critical review of the literature. Eur Spine J 2006; 15: Nilsson J, Fridén C, Burén V, Westman A, Lindholm P, Äng B. Musculoskeletal pain and related risks in skydivers: a population-based survey. Aviat Space Environ Med 2013; 84:

7 Neck pain in skydivers Independent risk factors found: >90 jumps in the last 12 months Main parachute wing-loading >1.4 lb/ft 2 Active skydivers using small parachutes may be at risk. So, we studied their muscles during their parachute openings. This is how we did it Nilsson J, Fridén C, Burén V, Westman A, Lindholm P, Äng B. Musculoskeletal pain and related risks in skydivers: a population-based survey. Aviat Space Environ Med 2013; 84:

8 (This is me) Methods Surface electromyography beneath the jumpsuit.

9 (This is me) Methods One accelerometer on the equipment (acc-rig). One accelerometer on the human at T1-T3 (acc-neck).

10 Methods

11 Methods Methods 20 experienced skydivers were recruited and scheduled for two consecutive belly-down terminal velocity skydives each. Two triaxial accelerometers (neck and rig). Acceleration was expressed as multiples of Earth s gravitational acceleration g using the dimensionless ratio G. Muscle activity was sampled with surface electromyography and expressed as the percentage of reference contractions. Muscle activity was defined as anticipatory if initiated 100 ms before to 50 ms after parachute opening shock onset. Two high speed cameras. No test subject adverse events. A detailed description of methods is published in: Gladh, K., Äng, B. O., Lindholm, P., Nilsson, J., & Westman, A. Decelerations and Muscle Responses During Parachute Opening Shock. Aviat Space Environ Med 2013; 84(11):

13 Results Results: There seems to be two temporal accelerometric phases. Early Max deceleration Late Max deceleration

14 Results Results: There seems to be two temporal accelerometric phases.

15 Results Results: There seems to be two temporal accelerometric phases.

16 Results Results: High onset rate in the early phase. Avg onset rate (early phase only)

17 Results Results: Supramaximal activation in some muscles. Maximum neck muscle activity magnitudes

18 Results Results: Anticipatory muscle activation. Neck muscle activity temporal onset

19 Methods Conclusions Conclusions There seems to be two temporal accelerometric phases: An early phase with an initial jerk in negative x: pulled backwards, suddenly. (Note: Long moment arm.) A late phase with the bulk of the opening shock in positive z: pulled upwards, hard. Decelerations in acc-neck vs. acc-rig differ in the early phase. The neck muscle activity during parachute opening shock was high, even supramaximal for some muscle groups. Temporal muscle activations suggest anticipatory motor control to be a strategy among experienced skydivers in order to protect the neck during parachute opening shock.

20 Methods Conclusions Future implications Accelerometer placement on the human body should be considered by researchers studying the effects of acceleration on the musculoskeletal system. Can sport parachute (and their reefing) systems be designed to have less dramatic early phase onset rates? Would it be a good idea to keep the head neutrally between the shoulders during parachute opening, to avoid flexion or extension moments? Would it be a good idea to manipulate the body orientation in the air at parachute deployment (for instance, be in a head-high position) to lower the neck flexion moment during the early phase, and facilitating entering the late phase of opening shock with the head in a neutral position? Would it be a good idea to slow down the fall rate to some specified degree before deploying the parachute?

21 Conclusions Methods The proper study of Mankind is Man. - Alexander Pope, 1734: An Essay on Man The most reliable instrument for measuring the varied effects of dynamic force on man is man. -John Paul Stapp

22 Thank You. Questions?

Neck Muscle EMG-Force Relationship and Its Reliability During Isometric Contractions

Lo Martire et al. Sports Medicine - Open (217) 3: DOI 1.116/s79-17-3-2 ORIGINAL RESEARCH ARTICLE Neck Muscle EMG-Force Relationship and Its Reliability During Isometric Contractions Riccardo Lo Martire