<PAGE>
 
                                                                      10(iii)(d)
III)(D)

                                THIRD AMENDMENT
                                      TO
               AMENDED AND RESTATED LOAN AND SECURITY AGREEMENT


     THIS THIRD AMENDMENT, dated as of December 17, 1997, among SUMMIT BANK, a
New Jersey Banking Corporation ("Lender"); and CYBEX INTERNATIONAL, INC., CYBEX
FINANCIAL CORPORATION, EAGLE PERFORMANCE SYSTEMS, INC., CYBEX FITNESS GERATE
VERTRIEBS, GMBH, GENERAL MEDICAL EQUIPMENT LIMITED, LUMEX BED SYSTEMS, TROTTER
INC., and TROTTER HOLDING COMPANY (collectively, the "Borrowers").

                                  BACKGROUND
                                  ----------

     The Lender and the Borrowers have heretofore entered into the Amended and
Restated Loan and Security Agreement dated June 16, 1997 (the "Loan Agreement").
On July 15, 1997 the Lender and the Borrower entered into a First Amendment to
Loan Agreement (hereinafter "First Amendment").  Thereafter, on August 11, 1997,
Lender and the Borrower entered into a Second Amendment to the Loan Agreement
(hereinafter "Second Amendment").  All capitalized terms utilized herein and not
otherwise defined have the respective meaning indicated in the Loan Agreement.
The parties desire to enter into this Third Amendment, to modify certain
financial covenants in the Loan Agreement and to ratify and confirm all the
terms and conditions of the Loan Agreement and the First Amendment.

     1.   Section 1.34 of the Loan Agreement is hereby amended to read in its
entirety as follows:

          1.34 "LOANS" shall mean the Revolving Loans, the Term Loan, the
               -------                                                   
Trotter Letter of Credit and the Lumex, Inc. $3,500,000.00 Revenue Note dated
December 18, 1983 ("LUMEX NOTE").

     2.   Section 1.36 of the Loan Agreement is hereby amended to read in its
entirety as follows:

          1.36 "NOTE" OR "NOTES"  means the Revolving Note, the Term Note and
               ------------------                                            
the Lumex Note executed and delivered by the Borrowers to the Lender to evidence
the Loans.

     3.   Section 1.37 of the Loan Agreement is hereby amended to read in its
entirety as follows:

          1.37 "OBLIGATIONS" shall mean any and all Revolving Loans, the Term
               -------------                                                 
Loan, the Trotter Letter of Credit, the Lumex Note and all other obligations,
liabilities and indebtedness of every kind, nature and description owing by
Borrowers to Lender and/or their affiliates, including principal, interest
charges, fees, costs and expenses, however evidenced, whether as principal,
surety, endorser, guarantor or otherwise, 
<PAGE>
 
whether arising under this Agreement or otherwise, whether now existing or
hereafter arising, whether arising before, during or after the initial or any
renewal term of this Agreement or after the commencement of any case with
respect to Borrowers under the United States Bankruptcy Code or any similar
statute (including, without limitation, the payment of interest and other
amounts which would accrue and become due but for the commencement of such
case), whether direct or indirect, absolute or contingent, joint or several, due
or not due, primary or secondary, liquidated or unliquidated, secured or
unsecured, and however acquired by Lender.

     4.   The Loan Agreement shall be amended by the addition of the following
paragraphs:

          4.1  LUMEX NOTE.    The Lender has on this date advanced the sum of
               -----------                                                    
$1,934,090.30 on behalf of the Borrowers and obtained an assignment from Norwest
Bank of a certain $3,500,000.00 Revenue Note dated December 28, 1983 (Lumex
Note).  The Lumex Note shall hereinafter be deemed part of Indebtedness as
defined in Paragraph 1.26 of this Agreement. The Borrowers acknowledge and agree
that all of the terms and conditions of the Loan Agreement shall be applicable
to the Lumex Note and the Indebtedness evidenced thereby.

          9.24 AMENDMENT TO LUMEX LOAN AGREEMENT.  Borrowers and Lender hereby
               ----------------------------------                             
specifically acknowledge and agree that the covenants contained in this
paragraph and this Agreement replace and amend the covenants contained in
Article Four of the Loan Agreement dated December 28, 1983, as heretofore
amended, between the City of Owatonna and Lumex, Inc. (now known as Cybex
International, Inc.), pursuant to which the Lumex Note was issued.

     5.   CONFIRMATION OF OBLIGATIONS.    This Third Amendment is made
          ----------------------------                                
supplemental to and a part of the Loan Agreement.  Except as expressly amended
and modified by this Third Amendment, the Loan Agreement, the First Amendment
and the Second Amendment, are hereby ratified and confirmed in all respects.
<PAGE>
 
     IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Third Amendment as of the date first above written.

Witness                             SUMMIT BANK


 /s/ Frank V. Tedesco               By: /s/ Adrian M. Marquez
------------------------------         ----------------------------
                                       Adrian M. Marquez, V.P.


Witness                             CYBEX INTERNATIONAL, INC.


 /s/ James H. Carll                 By: /s/ William Hurley
------------------------------         ----------------------------


Witness                             EAGLE PERFORMANCE SYSTEMS, INC.


 /s/ James H. Carll                 By: /s/ William Hurley
------------------------------         ----------------------------
 


Witness                             CYBEX FITNESS GERATE VERTRIEBS,
                                    GMBH


 /s/ James H. Carll                 By: /s/ William Hurley
------------------------------         ----------------------------
 


Witness                             GENERAL MEDICAL EQUIPMENT
                                    LIMITED


 /s/ James H. Carll                 By: /s/ William Hurley
------------------------------         ----------------------------
 
<PAGE>
 
Witness                             LUMEX BED SYSTEMS


 /s/  James H. Carll                By: /s/ William Hurley
------------------------------         ----------------------------


Witness                             TROTTER, INC.


 /s/  James H. Carll                By: /s/ William Hurley
------------------------------         ----------------------------


Witness                             TROTTER HOLDING COMPANY


 /s/  James H. Carll                By: /s/ William Hurley
------------------------------         ----------------------------