title: Nitrate supplementation enhances the contractile properties of human skeletal muscle.
abstract: OBJECTIVE
  Dietary nitrate supplementation positively affects cardiovascular function at rest and energy metabolism during exercise in humans and has recently also been reported to markedly enhance the in vitro contractile properties of mouse fast-twitch muscle. The aim of this study was to investigate the effects of short-term nitrate supplementation on the in vivo contractile properties of the skeletal muscle and voluntary muscle function of humans.
  
  
  METHODS
  In a double-blind, randomized, crossover design, 19 healthy untrained men (21 ± 3 yr) ingested a nitrate-rich concentrated beetroot juice (NIT; nitrate dosage, approximately 9.7 mmol·d) and a placebo (PLA) for seven consecutive days. After the last supplementation dose, force was recorded while participants completed a series of voluntary and involuntary (electrically evoked) unilateral isometric contractions of the knee extensors.
  
  
  RESULTS
  NIT enhanced the peak force response to low-frequency electrical stimulation, as follows: maximal twitch (NIT, 149 ± 41 N, vs PLA, 138 ± 37 N; P = 0.008; effect size, r (ES) = 0.56) and submaximal 1- to 20-Hz contractions (5%-10%, ES = 0.53-0.63). Whereas explosive (rising phase) force production during the first 50 ms of evoked maximal twitch and octet contractions (eight electrical impulses at 300 Hz) was also 3%-15% greater after NIT compared with that after PLA (P = 0.023-0.048, ES = 0.52-0.59), explosive voluntary force remained similar (P = 0.510, ES = 0.16). Maximum voluntary force was also unchanged after NIT (P = 0.539, ES = 0.15).
  
  
  CONCLUSIONS
  These results indicate that 7 d of dietary nitrate supplementation enhanced the in vivo contractile properties of the human skeletal muscle. Specifically, nitrate supplementation improved excitation-contraction coupling at low frequencies of stimulation and enhanced evoked explosive force production but did not affect maximum or explosive voluntary force production in untrained individuals.
authors.affiliation: School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM.
authors.forename: Georg
authors.initials: G
authors.lastname: Haider
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Folland
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D004558:Electric Stimulation; D004576:Electromyography; D005267:Femoral Nerve; D006801:Humans; D007717:Knee / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009566:Nitrates / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D009566:Nitrates