Analgesic Induces Similar Upper and Lower Body Pain Pressure Threshold Increases
Condition: Pain, Acute; Muscle Soreness; Tendon Injuries
MeSH terms: Myalgia; Acute Pain; Tendon Injuries
Study type: Interventional

Summary: 
      Background: Both health professionals and consumers use menthol-based topical analgesics
      extensively for the temporary relief of pain from musculoskeletal ailments or injury.
      However, there are no reports of differences in the pain pressure threshold (PPT) or the
      relative effectiveness of topical analgesics to reduce pain in the upper and lower body
      muscles and tendons. Objectives: The objective of this study was to investigate whether
      differences existed in PPT and relative pain attenuation associated with a menthol based
      topical analgesic over a variety of upper and lower body muscles and tendons. Design:
      Randomized allocation, controlled, intervention study. Method: Sixteen participants (10
      females and 6 males), who were tested on their dominant or non-dominant side. The order of
      specific muscle / tendon testing was also randomized, which included upper body (middle
      deltoid, biceps brachii, and lateral epicondylar tendon) and lower body locations
      (quadriceps, hamstrings, gastrocnemius, lumbo-sacral erector spinae muscles, and patellar and
      Achilles tendons). PPT was monitored before and 15-minutes following the application of a
      menthol based topical analgesic.
    

Detailed description: 
      Experimental Design Using random allocation (slip of paper chosen from a box by one of the
      researchers), participants were either tested on their dominant or non-dominant side. Limb
      dominance was determined by the participants' self-report of the preferred hand used for
      writing/throwing (upper extremity) and for kicking a ball (lower extremity). Further,
      randomization was used to determine which muscle groups would be tested first: upper body
      versus lower body, and the order of muscle testing. The tested upper body limb muscles
      consisted of the middle deltoid, and biceps brachii. The lower body muscle groups consisted
      of the quadriceps, hamstrings, and gastrocnemius. In order to compare sensitivity differences
      between muscles and tendons, the patellar tendon, and Achilles tendon were also tested. In
      addition, as tennis elbow (lateral epicondylitis/epicondylosis) is a common injury [40], the
      lateral epicondylar tendon was also evaluated. The lower back was tested using the
      lumbo-sacral erector spinae muscles.

      The pre-testing consisted of obtaining PPT (without topical analgesic application) using a
      handheld algometer (Lafayette Manual Muscle Test System™, Model 01163, Lafayette Instrument
      Company, Indiana, USA), from each muscle or tendon. The algometer was a hand-held muscle
      tester with a range of 0-300 pounds (136.1 kilograms) that consisted of a padded disc with a
      surface area of 1.7 cm2 attached to a microprocessor-control unit that measures peak force
      (pounds or kilograms). The unit has a digital readout for peak-applied pressure and provides
      a built-in calibration routine that verifies a valid calibration. The pain threshold was
      defined as the minimum pressure that induced pain [15]. Participants were instructed to
      provide a verbal report as soon as the quality of sensation changed from pressure to pain
      [15,16] at which point the algometer was removed. This study chose to measure the PPT via a
      pressure algometer as it has been shown to be a clinically and experimentally reliable method
      to assess pain [16,23,35]. The middle of the muscle belly for the biceps brachii, middle
      deltoid, hamstrings (biceps femoris), quadriceps (rectus femoris), and gastrocnemius was
      used. The measurement sites for the patella tendon and lateral epicondylar tendon were 1 cm
      distal from the bony origin. For the Achilles tendon, the measurement was taken at one third
      of the distance of the tendon length distal to its insertion. There were three readings from
      each testing position with a 5-second rest period between each reading.

      Intervention The intervention involved the application of 4% menthol-based Biofreeze®
      (Performance Health, Akron, Ohio) to the muscles and tendons immediately following the
      pre-testing. Based on prior recommendations [22,45,32] varying volumes of the topical
      analgesic were applied in reference to the surface area of the muscle. The previously cited
      investigators recommended 1ml per 200 cm2 of muscle surface area. No significant force (light
      stroking actions to apply the analgesic) was used for the application of the menthol-based
      topical analgesic.
    

Intervention name(s): Menthol based topical analgesic
Intervention type(s): Combination Product
Intervention description(s): Topical analgesic or placebo was applied to upper and lower body muscles and tendons and pain pressure threshold was measured with a handheld algometer.
Other intervention name(s): Menthol smelling cream with no analgesic
Intervention MeSH terms: Analgesics; Menthol
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Random allocation of the application of a menthol based topical analgesic versus a placebo.
Masking: Double (Participant, Investigator)
Primary purpose: Basic Science
Keywords: menthol; musculoskeletal; tendons; lower back