Ground reaction force patterns in plyometric push-ups.

Compared with lower extremity plyometrics, data concerning the loads and intensity associated with upper extremity plyometrics are limited. The purpose of this study was to compare vertical ground reaction force (vGRF) characteristics between the clap push-up and box drop push-ups from 3.8 cm (BD1), 7.6 cm (BD2), and 11.4 cm (BD3) heights and limbs (dominant, nondominant). Twenty-two healthy active male subjects (age 25.9 ± 1.3 years, height 1.8 ± 0.08 m, mass 87.6 ± 12 kg) performed 4 repetitions of each push-up variation in a random order. Four dependent variables, peak vGRF, time-to-peak vGRF, loading rate (LR), and propulsion rate (PR) were calculated for each extremity. Statistical analysis consisted of separate limb by variation repeated measures analysis of variance. In addition, ground contact time (GCT) was statistically compared between variations. The GCT for the clap push-up (p = 0.033) was significantly less than that for BD1 and BD2. No significant differences were revealed for time-to-peak vGRF (p = 0.717). Peak vGRF was significant between dominant and nondominant limbs (p = 0.045). Post hoc analysis of a significant limb by variation interaction in LR (p < 0.001) revealed the dominant limb to be significantly greater than the nondominant one in all 4 push-up variations. Furthermore, for both limbs, the clap LR was significantly greater than BD1, BD2, and BD3. The clap PR was significantly greater than BD1, BD2, and BD3. These data add rationale for determining upper extremity plyometric progression. The peak vGRFs are similar, and altering the box height did not affect peak vGRF. In contrast, the clap demonstrated the highest LR and PR suggesting that it may be a more powerful exercise than BD1, BD2, and BD3. The higher LR (Clap and BD3) for the dominant extremity illustrates bilateral disparity in the rate of eccentric loading.

Illicit stimulant use in humans is associated with a long-term increase in tremor.

Use of illicit stimulants such as methamphetamine, cocaine, and ecstasy is a significant health problem. The United Nations Office on Drugs and Crime estimates that 14-57 million people use stimulants each year. Chronic use of illicit stimulants can cause neurotoxicity in animals and humans but the long-term functional consequences are not well understood. Stimulant users self-report problems with tremor whilst abstinent. Thus, the aim of the current study was to investigate the long-term effect of stimulant use on human tremor during rest and movement. We hypothesized that individuals with a history of stimulant use would exhibit abnormally large tremor during rest and movement. Tremor was assessed in abstinent ecstasy users (n = 9; 22 ± 3 yrs) and abstinent users of amphetamine-like drugs (n = 7; 33 ± 9 yrs) and in two control groups: non-drug users (n = 23; 27 ± 8 yrs) and cannabis users (n = 12; 24 ± 7 yrs). Tremor was measured with an accelerometer attached to the index finger at rest (30 s) and during flexion and extension of the index finger (30 s). Acceleration traces were analyzed with fast-Fourier transform. During movement, tremor amplitude was significantly greater in ecstasy users than in non-drug users (frequency range 3.9-13.3 Hz; P<0.05), but was unaffected in cannabis users or users of amphetamine-like drugs. The peak frequency of tremor did not significantly differ between groups nor did resting tremor. In conclusion, abstinent ecstasy users exhibit an abnormally large tremor during movement. Further work is required to determine if the abnormality translates to increased risk of movement disorders in this population.