Deficits in muscle cross-sectional area and maximal isometric force following a shark bite injury are not reflected in jumping performance

Introduction: Environmental changes and growing surfing populations have led to increases in the number of shark sightings and unprovoked shark attacks on surfers. We present a case study of a 26-year-old male (height 178.4cm, mass 67.3kg) who was bitten by a shark on his left lateral thigh whilst surfing. The surfer lost most of the muscle and skin of the distal 2/3 of his anterolateral thigh, including all of vastus lateralis and most of vastus intermedius and rectus femoris muscles. After 3 years of intensive physiotherapy and rehabilitation, the surfer returned to a high-level of competitive surfing and has remarkable physical function. We investigated the anatomical structure and function of his affected (A) and unaffected (UA) thigh muscles relative to his dynamic functional strength to understand the potential physical function that can be achieved despite substantial muscle loss. Methods: Muscle group cross-sectional area (CSA) for the quadriceps and hamstrings were measured using magnetic resonance imaging, with axial slices taken from ~50% of the distance between the lesser trochanter and the medial femoral condyle. A handheld dynamometer was used to assess the maximal isometric strength of the quadriceps muscles through resisted knee extension while the surfer was seated and the hamstring muscles through resisted knee flexion in a prone position. Dynamic strength and jumping performance were assessed by the surfer performing countermovement jumps (CMJ) on two force platforms. Data are reported as means ± standard deviations. Results: The surfer’s quadriceps CSA was substantially larger in the UA (8304.8mm2) compared to the A (2857.2mm2) limb, although there was little between-limb difference in hamstring CSA (UA: 3499.1mm2, A: 3273.6mm2). The surfer produced more maximal isometric quadriceps strength in the UA compared to the A limb (406.1±45.0N vs 205.9±12.6N). The surfer’s peak CMJ height was 34±1.0cm, with relative peak forces of 1.28±0.10N/BW and 0.82±0.03N/BW generated for the UA and A, respectively. Discussion: Differences in quadriceps muscle function between the limbs were consistent with the differences in anatomical structure, whereby lower quadriceps CSA resulted in lower maximal isometric quadriceps strength. This quadriceps strength deficit, however, was not reflected in the functional dynamic strength achieved in the CMJ because the surfer’s peak jump height was comparable to that of international-level competitive surfers. Differences in the between-limb peak forces were much less than differences in maximal isometric strength, suggesting that neuromuscular adaptations developed during rehabilitation might have contributed to the high-level of physical function the surfer achieved. Conflict of interest statement: The authors have no conflicts of interest to declare.