Browsing by Author "Aagaard, Per"

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    Lower Limb Asymmetry in Mechanical Muscle Function: A Comparison Between Ski Racers With and Without ACL Reconstruction
    (Scandinavian Journal of Medicine and Science in Sports, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, Per
    Due to a high incidence of anterior cruciate ligament (ACL) re-injury in alpine ski racers, the aim was to assess functional asymmetry in the countermovement jump (CMJ), squat jump (SJ) and leg muscle mass in elite ski racers with and without anterior cruciate ligament reconstruction (ACL-R). Elite alpine skiers with ACL-R (n=9; 26.2±11.8 months post-op) and uninjured skiers (n=9) participated in neuromuscular screening. Vertical ground reaction force during the CMJ and SJ was assessed using dual force plate methodology to obtain phase-specific bilateral asymmetry indices (AI) for kinetic impulse (CMJ and SJ phase-specific kinetic impulse AI). Dual X-Ray absorptiometry (DXA) scanning was used to assess asymmetry in lower body muscle mass. Compared to controls, ACL-R skiers had increased AI in muscle mass (P<0.001), kinetic impulse AI in the CMJ concentric phase (P<0.05) and the final phase of the SJ (P<0.05). Positive associations were observed between muscle mass and AI in the CMJ concentric phase (r=0.57, P<0.01) as well as in the late SJ phase (r=0.66, P<0.01). Future research is required to assess the role of the CMJ and SJ phase-specific kinetic impulse asymmetry index as a part of a multi-faceted approach for improving outcome following ACL-R in elite ski racers.
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    Neuromuscular Function and Performance in Alpine Ski Racers with Anterior Cruciate Ligament Reconstruction: A Return to Sport Framework
    (2017) Jordan, Matthew J; Herzog, Walter; Aagaard, Per; Heard, Mark; Doyle-Baker, Patricia; Kolb, Jon; Holmberg, Hans-Christer; Edwards, Brent
    The primary aim of this study was to evaluate the effects of ACL injury on neuromuscular function in elite alpine ski racers, and to monitor skiers throughout the return to sport transition. In Chapter 2 a narrative review of the literature was performed on ACL injury, ACL re-injury, and return to sport after ACL injury in ski racing. In Chapter 3, a new test of inter-limb functional asymmetry was used to evaluate alpine ski racers with/without ACL reconstruction (ACLR). Despite a full return to competition, ACLR ski racers demonstrated elevated inter-limb functional asymmetries that were correlated with lower limb muscle mass asymmetry. In Chapter 4, hamstring/quadriceps strength ratios were measured in ski racers with/without ACLR. ACLR ski racers displayed significant hamstring/quadriceps strength deficits in the ACLR limb compared to the contralateral limb and the limb average of non-injured skiers. In Chapter 5, the functional lower-limb asymmetry test introduced in Chapter 3 was used to evaluate the acute effects of a fatiguing jump protocol on asymmetry and hamstring/quadriceps muscle activity in ski racers with/without ACLR. The ACLR skiers displayed systematic inter-limb functional asymmetries. ACLR skiers displayed reduced quadriceps muscle activity at takeoff in the surgical limb. Both the ACLR group and non-injured controls became quadriceps dominant with fatigue. Quadriceps muscle activity increased while hamstring muscle activity decreased. Notably, this was found in the pre-landing phase. In Chapter 6, primary ACLR operative reports from 28 skiers were analyzed to evaluate the associated pathology including multi-ligament injury, meniscal tears and chondral lesions. Operative reports from future surgeries were analyzed to evaluate the injury progression. At the time of primary ACLR, there was a higher proportion of chondral lesions in the lateral compartment compared to the medial compartment, and complex meniscal tears compared to one-dimensional tears. At the time point of future surgery, a significant proportion of skiers showed a worsening of chondral lesions, including half of the skiers presenting with Grade 3 or Grade 4 lesions. Functional asymmetry was also evaluated at various time points following primary ACLR. Nearly two years were required for functional asymmetry indices to reach values comparable to those of non-injured ski racers.
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    Rapid Hamstring/Quadriceps Strength in ACL Reconstructed Elite Alpine Ski Racers
    (Medicine and science in sports and exercise, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, Per
    Due to the importance of hamstrings (HAM) and quadriceps (QUAD) strength for anterior cruciate ligament (ACL) injury prevention, and the high incidence of ACL injury in ski racing, HAM and QUAD maximal and explosive strength was assessed in ski racers with and without ACL reconstruction (ACL-R).
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    A Return to Skiing Envelope of Function for Anterior Cruciate Ligament Reconstructed Elite Alpine Ski Racers
    (Science and Skiing VI, 2016) Herzog, Walter; Jordan, Matthew; Aagaard, Per
    Elite alpine ski racing comprises bidirectional turning with forceful concentric but predominantly eccentric contractions that create large quadriceps muscle loading and hamstrings/quadriceps muscle co-contraction (4, 10). Ski racing also occurs in an unpredictable environment where skiers are at an increased risk for lower body injury, especially to the knee joint and the anterior cruciate ligament (ACL) (2, 3, 8, 15). Unlike field sports, there are no sex-differences in ACL injury rates due to the preclusion of sex-related risk factors resulting from the large forces and unique mechanisms of ACL injury (8, 15).