ABSTRACT
BACKGROUND: An increased risk of ACL injury has been shown in female athletes who land from jumping maneuvers with knee angles close to extension and in those who demonstrate a hamstring-to-quadriceps muscle recruitment imbalance. HYPOTHESIS/PURPOSE: The purpose of this study was to determine if added heel lift height would alter electromyography (EMG) magnitude and timing of the quadriceps (vastus medialis, vastus lateralis), hamstrings (semitendinosus, biceps femoris) and gastroc (medial gastroc, lateral gastroc) musculature during forward jump and drop-rebound jump landing tasks in females. The authors hypothesized increased heel lift height would promote recruitment of the hamstring and gastrocnemius muscles and increase the time to peak muscle activity in the quadriceps muscles. STUDY DESIGN: Prospective randomized trial. METHODS: 60 recreationally active females participated. Participants performed five repetitions of forward jump and drop-rebound jump landing tasks while wearing different heel lifts heights (0, 12, 18, 24 mm) placed on the under-side of an athletic shoe. Task order and heel lift height were randomized. Dependent measures were average magnitude of muscle recruitment (AMR), peak magnitude of muscle recruitment (PMR), and time to reach PMR for six lower extremity muscle groups as measured by surface EMG. RESULTS: Repeated measures ANOVAs were used to determine the influence of heel lift height on the dependent measures. There were no signficant differences in the AMR, PMR, or time to reach PMR with the four different heel heights during the landing maneuvers, with one exception. A significant difference was found in the time to achieve PMR in the semitendinosis muscle during a forward jump landing (p = .024). Post hoc analysis found significant differences with both the 18mm and 24mm heel lift height compared to 0mm. CONCLUSIONS: Utilization of larger heel lifts (18mm and 24mm) to influence landing biomechanics may be of potential benefit; however, only when performing forward jump landing tasks. Further investigation into the protective effects of a quicker onset of semitendinosis peak magnitude is warranted. LEVEL OF EVIDENCE: 2.
ABSTRACT
Wheat straw can serve as a low-cost substrate for energy production without competing with food or feed production. This study investigated the effect of steam explosion pretreatment on the biological methane potential and the degradation kinetics of wheat straw during anaerobic digestion. It was observed that the biological methane potential of the non steam exploded, ground wheat straw (276 l(N) kg VS(-1)) did not significantly differ from the best steam explosion treated sample (286 l(N) kg VS(-1)) which was achieved at a pretreatment temperature of 140°C and a retention time of 60 min. Nevertheless degradation speed was improved by the pretreatment. Furthermore it was observed that compounds resulting from chemical reactions during the pretreatment and classified as pseudo-lignin were also degraded during the anaerobic batch experiments. Based on the rumen simulation technique, a model was developed to characterise the degradation process.