INTRODUCTION: Mechanical efficiency(ME) may be a contributing factor in running performance. ME is the ratio between the amount of mechanical work performed and the amount of energy expended during exercise. PURPOSE: The purpose of this investigation was to determine the possible differences in ME and percent changes in ME with repetitive hopping between competitive and recreational long distance runners. METHODS: Nine male runners (age 20±1.05yrs; height 69.69±3.3in; weight 70±14.9kg) who ran at least 3 days a week were recruited. Participants reported to the lab on 2 days, separated by 1 week. On the first day, height, weight, and VO2max were measured. On the second day, participants completed 10 minutes of hopping on a force plate to determine ME. Subjects were classified as ‘recreational’ (Rec) or ‘competitive’ (Comp) based on their self reported 1600m time and their VO2 max (rec: VO2max<60.0 ml/kg/m, 1600 time≥5:00; com: VO2max≥60.0 ml/kg/m, 1600m time<5:00). RESULTS: The recreational group had a mean VO2max of 51.9±1.57 ml/kg/m, ME of 38.7±7.00%, and % change in ME of 29.9±16.6%. The competitive group had a mean VO2max of 64.1±3.8, ME of 43.29±9.45%, % change in ME of 14.6±5.17%. Percent change in ME between groups trends toward significance (p=0.14). A correlation was observed between VO2max and % change in ME that trended toward significance (r=-0.58, p=0.10). PRACTICAL APPLICATION: It appears that individuals categorized as competitive may maintain ME better than recreational runners (i.e. lower % change in ME). The ability to maintain ME during long duration stretch-shortening cycle exercise may be a factor pertaining to running performance.
INTRODUCTION
Acute ACL injury can be devastating, and often results in clinical sequelae including long-term disability and osteoarthritis. To study loading factors independently and in combination, such a model must be capable of consistent independent control of each parameter. We hypothesized that an unconstrained test configuration capable of independent application of loads about all anatomical axes of loading would allow us to evaluate each mode of loading separately an in combination, while generating realistic injuries patterns.
METHODS
19 cadaveric legs (45±7 years) were tested under multiple combinations of anterior shear, abduction and internal rotation moments utilizing a novel drop stand. Landing was simulated by releasing either half or full body weight from 30 or 60 cm above the foot. Specimens were tested at 25o of flexion under simulated muscle loads. Joint kinematics and ACL strain were collected.
RESULTS and DISCUSSION
Our test setup was able to deliver a consistent impact load-time history. Experiments produced ACL failure in the majority of specimens. A clinically relevant distribution of failure patterns was observed. Detailed attention to impact parameters including mass, drop height and interface helped to generate an in vitro load-time history similar to in vivo data. This setup was designed to replicate the ranges of loading determined from in vivo studies of ACL injury mechanisms undertaken by our group. This evolution of experimental design facilitates the use of this experimental model to independently evaluate the effects of single and multi-axis loads on ACL injury, while recreating injury patterns observed in vivo.
The purpose of this study was to quantify the external moments and digit-tip forces acting on a freely moveable object while old (OA; 60-85 years) and young (YA; 18-50 years) adults performed functionally-relevant tasks. Able-bodied participants performed a grasp and lift task, and a precision-orientation (key-slot) task akin to inserting a key in the hole using a precision (thumb-index finger) grip. During the grasp-lift task the OA group misaligned their thumb and finger contacts, and produced greater grip force, greater external moments on the object around its roll axis, and oriented force vectors differently compared to the YA group. During the key-slot task, the OA group was more variable in digit-tip force directions and performed the key-slot task more slowly. With practice the OA group aligned their digits, reduced their grip force, and minimized external moments on the object, clearly demonstrating that the nervous system monitored and actively manipulated one or more variables related to object tilt. This was true even for the grip-lift task; a task for which no instructions regarding object orientation were given and which could tolerate modest amounts of object tilt without interfering with task goals. Although the OA group performed the key-slot task faster with experience, they remained slower than the YA group. We conclude that with old age comes a reduced ability to appropriately position their digits on an object, and then control the forces and moments applied to objects during precision grasp and manipulation. This may contribute to the ubiquitous slowing and deteriorating manual dexterity in healthy aging.