title: A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings.
abstract: Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface. Although previous researchers have noted some differences between these tasks across separate studies, little research has compared these tasks in the same study. Thus, we examined whether a subsequent movement after initial landing alters muscle activity and kinetics between drop landings and jumps. Fifteen women performed 10 drop landings and drop jumps each from 45 cm. Muscle onsets and integrated muscle activation amplitudes 150 milliseconds before (preactivity) and after landing (postactivity) in the medial and lateral quadriceps, hamstrings, and lateral gastrocnemius and peak and time-to-peak vertical ground reaction forces were examined across tasks (p ≤ 0.05). When performing drop jumps, subjects demonstrated later (p = 0.02) gastrocnemius and lesser lateral gastrocnemius (p = 0.002) and medial quadriceps (p = 0.02) preactivity followed by increased postactivity in all muscles (p = 0.006), with higher peak vertical ground reaction forces (p = 0.04) but no differences in times to these peaks (p = 0.60) than drop landings. The later gastrocnemius activation, higher gastrocnemius and quadriceps postlanding amplitudes, and higher ground reaction forces in drop jumps may allow subjects to propel the body vertically after the initial landing vs. simply absorbing impact in drop landings. Our results indicate that in addition to landing surface and height, anticipation of a subsequent task changes landing neuromechanics. Generalizations of results from landing-only studies should not be made with landing followed-by-subsequent-activity studies. Landing exercises should be incorporated based on sport-specific demands.
authors.affiliation: Sports Medicine Assessment Research and Testing Laboratory, George Mason University, Manassas, Virginia, USA. jambegao@gmu.edu
authors.forename: Jatin P
authors.initials: JP
authors.lastname: Ambegaonkar
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
authors.forename: David H
authors.initials: DH
authors.lastname: Perrin
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D013177:Sports / Q000502:physiology*; D055815:Young Adult