Ken Anderson

MAINTENANCE OF EMG ACTIVITY AND LOSS OF FORCE OUTPUT WITH INSTABILITY

&NA; Anderson, K.G., and D.G. Behm. Maintenance of EMG activity and loss of force output with instability. J. Strength Cond. Res. 18(3):637–640. 2004.—Swiss Balls used as a platform for training provide an unstable environment for force production. The objective of this study was to measure differences in force output and electromyographic (EMG) activity of the pectoralis major, anterior deltoid, triceps, latissimus dorsi, and rectus abdominus for isometric and dynamic contractions under stable and unstable conditions. Ten healthy male subjects performed a chest press while supported on a bench or a ball. Unstable isometric maximum force output was 59.6% less than under stable conditions. However, there were no significant differences in overall EMG activity between the stable and unstable protocols. Greater EMG activity was detected with concentric vs. eccentric or isometric contractions. The decreased balance associated with resistance training on an unstable surface may force limb musculature to play a greater role in joint stability. The diminished force output suggests that the overload stresses required for strength training necessitate the inclusion of resistance training on stable surfaces.

The Impact of Instability Resistance Training on Balance and Stability

AbstractThe most predominant literature regarding balance has emphasised the physiological mechanisms controlling stability. Topics range from extrinsic factors (environment) to intrinsic factors (i.e. muscle coordination, vestibular response). Balance is achieved through an interaction of central anticipatory and reflexive actions as well as the active and passive restraints imposed by the muscular system. However, less research has attempted to document the effects of balance on performance measures (i.e. force, power). Furthermore, short- and long-term adaptations to unstable environments need more substantial research. While force and other performance measures can be adversely affected by a lack of balance, the transferability of instability training to activities of daily living and sport is not precisely known. The applicability of instability and resistance training using unstable platforms or implements may have strong relevance in a rehabilitative or athletic setting. Therefore, a comprehensive review of the literature in this area may possibly be of benefit to practitioners who deal with the general population, athletes or persons debilitated by balance and/or stability disabilities.

The Role Of Instability With Resistance Training

There are many instances in daily life and sport in which force must be exerted when an individual performing the task is in an unstable condition. Instability can decrease the externally-measured force output of a muscle while maintaining high muscle activation. The high muscle activation of limbs and trunk when unstable can be attributed to the increased stabilization functions. The increased stress associated with instability has been postulated to promote greater neuromuscular adaptations, such as decreased co-contractions, improved coordination, and confidence in performing a skill. In addition, high muscle activation with less stress on joints and muscles could also be beneficial for general musculoskeletal health and rehabilitation. However, the lower force output may be detrimental to absolute strength gains when resistance training. Furthermore, other studies have reported increased co-contractions with unstable training. The positive effects of instability resistance training on sports performance have yet to be quantified. The examination of the literature suggests that when implementing a resistance training program for musculoskeletal health or rehabilitation, both stable and unstable exercises should be included to ensure an emphasis on both higher force (stable) and balance (unstable) stressors to the neuromuscular system.

Relationship between hockey skating speed and selected performance measures.

The objective of this study was to determine the relationship between specific performance measures and hockey skating speed. Thirty competitive secondary school and junior hockey players were timed for skating speed. Off-ice measures included a 40-yd (36.9-m) sprint, concentric squat jump, drop jump, 1 repetition maximum leg press, flexibility, and balance ratio (wobble board test). Pearson product moment correlations were used to quantify the relationships between the variables. Electromyographic (EMG) activity of the dominant vastus lateralis and biceps femoris was monitored in 12 of the players while skating, stopping, turning, and performing a change-of-direction drill. Significant correlations (p < 0.005) were found between skating performance and the sprint and balance tests. Further analysis demonstrated significant correlations between balance and players under the age of 19 years (r = −0.65) but not those over 19 years old (r = −0.28). The significant correlations with balance suggested that stability may be associated with skating speed in younger players. The low correlations with drop jumps suggested that short contact time stretch-shortening activities (i.e., low amplitude plyometrics) may not be an important factor. Electromyographic activities illustrated the very high activation levels associated with maximum skating speed.

Identifying visual–vestibular contributions during target-directed locomotion

The purpose of this experiment was to examine the potential interaction between visual and vestibular inputs as participants walked towards 1 of 3 targets located on a barrier 5m away. Visual and vestibular inputs were perturbed with displacing prisms and galvanic vestibular stimulation (GVS), respectively. For each target there were three vision conditions (no prisms, prisms left, and prisms right), and three GVS conditions (no GVS, anode left, and anode right). Participants were instructed to start with eyes closed, and to open the eyes at heel contact of the first step. GVS and target illumination were triggered by the first heel contact. This ensured that the upcoming visual condition and target were unknown and that both sensory perturbations occurred simultaneously. Lateral displacement was determined every 40 cm. Irrespective of target or direction, GVS or prism perturbation alone resulted in similar lateral deviations. When combined, the GVS and prism perturbations that had similar singular effects led to significantly larger deviations in the direction of the perturbations. The deviations were approximately equal to the sum of the single deviations indicating that the combined effects were additive. Conflicting GVS and prism perturbations led to significantly smaller deviations that were close to zero, indicating that opposite perturbations cancelled each other. These results show that when both visual and vestibular information remain important during task performance, the nervous system integrates the inputs equally.

Holographic data storage: science fiction or science fact?

To compete in the archive and backup industries, holographic data storage must be highly competitive in four critical areas: total cost of ownership (TCO), cost/TB, capacity/footprint, and transfer rate. New holographic technology advancements by Akonia Holographics have enabled the potential for ultra-high capacity holographic storage devices that are capable of world record bit densities of over 2-4Tbit/in2, up to 200MB/s transfer rates, and media costs less than

Progress in second-generation holographic data storage

10/TB in the next few years. Additional advantages include more than a 3x lower TCO than LTO, a 3.5x decrease in volumetric footprint, 30ms random access times, and 50 year archive life. At these bit densities, 4.5 Petabytes of uncompressed user data could be stored in a 19” rack system. A demonstration platform based on these new advances has been designed and built by Akonia to progressively demonstrate bit densities of 2Tb/in2, 4Tb/in2, and 8Tb/in2 over the next year. Keywords: holographic

Holographic data storage: rebirthing a commercialization effort

Holographic data storage (HDS) remains an attractive technology for big data. We report on recent results achieved with a demonstrator platform incorporating several new second-generation techniques for increasing HDS recording density and speed. This demonstrator has been designed to achieve densities that support the multi-terabyte storage capacities required for a competitive product. It leverages technology from an existing state-of-the-art pre-production prototype, while incorporating a new optical head designed to demonstrate several new technical advances. The demonstrator employs the new technique of dynamic aperture multiplexing in a monocular architecture. In a previous report, a monocular system employing angle-polytopic multiplexing achieved a recording density over 700 Gbit/in2, exceeding that of contemporaneously shipping hard drives [1]. Dynamic aperture multiplexing represents an evolutionary improvement with the potential to increase this figure by over 200%, while still using proven anglepolytopic multiplexing in a monocular architecture. Additionally, the demonstrator is capable of two revolutionary advances in HDS technology. The first, quadrature homodyne detection, enables the use of phase shift keying (PSK) for signal encoding, which dramatically improves recording intensity homogeneity and increases SNR. The second, phase quadrature holographic multiplexing, further doubles density by recording pairs of holograms in quadrature (QPSK encoding). We report on the design and construction of the demonstrator, and on the results of current recording experiments.

Holographic data storage at 2+ Tbit/in2

The realization of a commercial holographic data storage device has remained elusive for many decades. The most recent efforts were by InPhase Technologies between 2001 and 2009 resulting in 52 functioning prototypes capable of 300GB/disk and 20MB/s transfer rates. Despite being the world’s first fully functional holographic drives, the primary competitor to holographic archive storage at that time, LTO, had already achieved 800GB and 120MB/in 2008; and by 2010, LTO had achieved 1.5TB and 140MB/s. This left InPhase at a competitive disadvantage to LTO archive solutions despite other strengths such as robustness, random access, and longer-term archive lifetime. Looking into the future, holographic data storage must be highly competitive with tape in three critical areas: cost/TB, capacity/footprint, and transfer rate. If this can be achieved, holographic data storage would become a superior solution given the low latencies and overall robustness to propel it into being the archive storage front-runner. New technology advancements by Akonia Holographics have enabled the potential for ultra-high capacity holographic storage devices that are capable of world record bit densities of over 2Tbit/in2, 200-300MB/s transfer rates, and a media cost less than

Multi-terabit/in2 holographic data storage demonstration

10/TB in the next 5 years. A demonstration platform based on these new advances has been designed and is currently being built by Akonia to progressively demonstrate bit densities of 2Tb/in2, 4Tb/in2, and 8Tb/in2 over the next year.